Phthalide compound and a near infrared absorber and a recording material each comprising the same compound
FIELD OF THE INVENTION 
     This invention relates to a phthalide compound and a near infrared absorber and a recording material each comprising the same compound. More particularly, the invention relates to a novel phthalide compound and a near infrared absorber and a recording material each absorbing strongly the near infrared region but absorbing little the visible region of the spectrum. 
     BACKGROUND OF THE INVENTION 
     Recording materials utilizing the color reaction between an electron-donating color former (hereinafter referred to briefly as a color former) and an electron-accepting developer (hereinafter referred to briefly as a developer) are well known and particularly pressure-sensitive recording materials and thermo-sensitive recording materials are in broad use today. 
     Recently has increased a need for reading the image recorded on such a pressure-sensitive or thermo-sensitive recording materials with an optical character reader (hereinafter referred to as the OCR) utilizing a light-emitting diode, a semiconductor laser or the like as the light source. In order to read a recorded image with the OCR, it is essential that the image should have an absorption at the emission wavelength of the light source used. While the emission wavelength range of the OCR varies with different light sources used, light sources with emission wavelengths in the range of 650-750 nm are in the focus of current interest and, therefore, the recorded image preferably absorbs this particular wavelength range. 
     As for color formers providing recorded images absorbing the near infrared region of the spectrum, a number of compounds are already known. For example, as phthalide compounds capable of providing recorded images absorbing the wavelength range of about 650-750 nm, compounds (Compound A, B, C and D) of the following formulas are disclosed in U.S. Pat. No. 4,119,776 at col. 21, lines 36-68 of the specification. ##STR3## 
     Recording materials utilizing these known phthalide compounds provide recorded images that absorb the visible region as well and are, therefore, blue-bluish green-green in color, thus insuring the advantage that the recorded images are visible to the eye. However, these materials are not satisfactory in applications where visible color development is undesirable. Thus, there are cases in which the recorded image is preferably invisible as it is true with bank customer secret codes or in which the print is preferably inconspicuous for aesthetic reasons as it is true with bar codes. Moreover, when a fluorane compound not absorbing the near infrared region and providing for a black image is used in an OCR-compatible black recording material, the use thereof in combination with any known phthalide compound tends to result in the change of color. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a novel phthalide compound that, on reacting with a developer, absorbs strongly the near infrared region of the spectrum but does not absorb at all or absorbs only weakly the visible region. 
     It is a further object of this invention to provide a near infrared absorber that absorbs strongly the near infrared region but does not absorb at all or absorbs only weakly the visible region, that is to say that, by itself, is close to be colorless or white but absorbs the near infrared region and its uses. 
     It is a still further object of this invention to provide a recording material of the color former-developer type that provides for a recorded image that is either colorless or of pale color but absorbs strongly the near infrared region and a recording material including other color formers that does not undergo any appreciable change in color and absorbs strongly the near infrared region. 
     This invention relates, in one aspect, to a phthalide compound of general formula (I) and a process for producing the same compound. ##STR4## wherein ring A represents a substituent group of the following structural formula ##STR5## R 1  represents hydrogen, alkyl, alkoxy or halogen; n is an integer equal to 1 through 3, inclusive; ring B represents a substituent group of the following structural formula ##STR6## R 2  represents alkyl or aryl; R 3  represents alkyl; R 4  and R 5  independently represent alkyl or unsubstituted or substituted phenyl; R 6  represents hydrogen, alkyl or alkoxy. 
     This invention relates, in another aspect, to a near infrared absorber that is obtainable by reacting a phthalide compound of general formula (I) with an electron-accepting compound and a near infrared absorbent composition containing said infrared absorber. 
     This invention relates, in a further aspect, to a recording material utilizing the reaction between an electron-donating color former and an electron-accepting developer, which utilizes a phthalide compound of general formula (I) as said electron-donating color former. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an infrared absorption spectrum of compound 1 as synthesized in Example 1; 
     FIG. 2 is an infrared absorption spectrum of compound 13 as synthesized in Example 2; 
     FIG. 3 is an infrared absorption spectrum of compound 41 as synthesized in Example 4; 
     FIG. 4 is an infrared absorption spectrum of compound 57 as synthesized in Example 5; 
     FIG. 5 is an infrared absorption spectrum of compound 70 as synthesized in Example 6; 
     FIG. 6 is an infrared absorption spectrum of compound 87 as synthesized in Example 8; 
     FIG. 7 is an infrared absorption spectrum of compound 89 as synthesized in Example 9; 
     FIG. 8 is an infrared absorption spectrum of compound 91 as synthesized in Example 10; 
     FIG. 9 is an infrared absorption spectrum of compound 92 as synthesized in Example 11; 
     FIG. 10 is an infrared absorption spectrum of compound 97 as synthesized in Example 12; 
     FIG. 11 is an infrared absorption spectrum of compound 98 as synthesized in Example 13; 
     FIG. 12 is an infrared absorption spectrum of compound 108 as synthesized in Example 14; 
     FIG. 13 is an infrared absorption spectrum of compound 144 as synthesized in Example 15; 
     FIG. 14 is an infrared absorption spectrum of compound 155 as synthesized in Example 16; 
     FIG. 15 is an absorption spectrum of the glass sheet coated with the near infrared absorber produced from compound 1 and PHB as manufactured in Example 17; 
     FIG. 16 is an absorption spectrum of the glass sheet coated with the near infrared absorber produced from compound A and PHB as manufactured in Comparison Example 1; 
     FIG. 17 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 1 and bisphenol A as manufactured in Example 18; 
     FIG. 18 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound A and bisphenol A as manufactured in Comparison Example 2; 
     FIG. 19 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 13 and TG-SA as manufactured in Example 28; 
     FIG. 20 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 23 and D-8 as manufactured in Example 34; 
     FIG. 21 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 41 and bisphenol S as manufactured in Example 45; 
     FIG. 22 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 57 and PHB as manufactured in Example 51; 
     FIG. 23 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 87 and bisphenol A as manufactured in Example 61; 
     FIG. 24 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 89 and PHB as manufactured in Example 66; 
     FIG. 25 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 91 and bisphenol A as manufactured in Example 67; 
     FIG. 26 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 92 and D-8 as manufactured in Example 71; 
     FIG. 27 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 97 and PHB as manufactured in Example 75; 
     FIG. 28 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 98 and bisphenol A as manufactured in Example 76; 
     FIG. 29 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 108 and bisphenol A as manufactured in Example 79; 
     FIG. 30 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 144 and D-8 as manufactured in Example 83; 
     FIG. 31 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound 155 and D-8 as manufactured in Example 86; and 
     FIG. 32 is a reflection spectrum of the sheet of paper coated with the near infrared absorber produced from compound B and bisphenol A as manufactured in Comparison Example 13. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the above general formula (I), the alkyl for R 1  on ring A is not critical in absorption character but from the standpoint of availability of the starting material, is preferably an alkyl group of 1-8 carbon atoms and, for still better results, a C 1-6  alkyl group. Thus, R 1  may for example be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl or 2-ethylhexyl. The alkoxy for R 1  is preferably a lower alkoxy group of 1-4 carbon atoms and, for still better results, a C 1-2  alkoxy group. Thus, for example, metoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy and isobutoxy can be mentioned. The halogen for R 1  is preferably chlorine, bromine or fluorine and, for still better results, chlorine. The integer n is preferably equal to 1 or 2. 
     The alkyl for R 2  is preferably a lower alkyl group of 1-4 carbon atoms and, for still better results, a C 1-2  alkyl group. Thus, for example, methyl, ethyl, n-propyl and n-butyl can be mentioned. The aryl for R 2  is preferably phenyl or substituted phenyl, the preferred substituent of which is alkyl or halogen. Thus, said substituted phenyl may for example be o-tolyl, m-tolyl, p-tolyl, 2,4-xylyl, o-chlorophenyl, m-chlorophenyl or p-chlorophenyl. 
     R 3  is preferably an alkyl group of 1-12 carbon atoms and, for still better results, a C 1-8  alkyl group. Thus, the alkyl R 3  includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-decyl and n-dodecyl, among others. 
     The alkyl for R 4 , R 5  is preferably an alkyl group of 1-8 carbon atoms and, for still better results, a C 1-6  alkyl group. Thus, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl can be mentioned as examples. The aryl for R 4 , R 5  is preferably phenyl or substituted phenyl as preferably substituted by alkyl, alkoxy or halogen. Thus, said substituted phenyl includes o-tolyl, p-tolyl, m-tolyl, p-ethylphenyl, 2,4-xylyl, o-methoxyphenyl, m-metholxyphenyl, p-methoxyphenyl, p-ethoxyphenyl, o-chlorophenyl, m-chlorophenyl and p-chlorophenyl, among others. 
     The alkyl for R 6  is preferably an alkyl group of 1-4 carbon atoms, thus including methyl, ethyl, n-propyl, n-butyl and so on. The alkoxy for R 6  is preferably an alkoxy group of 1-8 carbon atoms and, for still better results, a C 1-6  alkoxy group. Thus, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy and n-hexyloxy can be mentioned by way of example. 
     The preferred combination of these substituents is as follows. 
     Ring A is ##STR7## R 1  is hydrogen, C 1-8  alkyl, C 1-4  alkoxy or halogen; R 2  is C 1-4  alkyl or unsubstituted or substituted phenyl; R 3  is C 1-12  alkyl; R 4  and R 5  each is C 1-8  alkyl or unsubstituted or substituted phenyl; R 6  is hydrogen, C 1-4  alkyl or C 1-8  alkoxy; and ring B is ##STR8## The more desirable combination of the substituents is that ring A is ##STR9## R 1  is hydrogen, C 1-6  alkyl, C 1-2  alkoxy or chlorine; R 2  is C 1-2  alkyl or phenyl; R 3  is C 1-8  alkyl; R 4  and R 5  each is C 1-6  alkyl or unsubstituted or substituted phenyl; R 6  is hydrogen, C 1-4  alkyl or C 1-6  alkoxy; and ring B is ##STR10## 
     The phthalide compounds of general formula (I) wherein R 1  or R 6  is an alkoxy group may provide for colored images on reacting with a developer but since the developed colors are gray series colors, they are particularly preferred in terms of shade for use in black image-producing recording materials containing other black-producing color formers. 
     The phthalide compound (I) of this invention (hereinafter referred to as the compound of the invention) can be synthesized by, inter alia, reacting an ethylene compound of general formula (II) with a benzoic acid derivative of general formula (III) in the presence of a dehydrative condensing agent. ##STR11## wherein ring A, ring B&#39;, and R 2  -R 6  are as defined hereinbefore. 
     The dehydrative condensing agent that can be used includes acetic anhydride, a mixture of glacial acetic acid and concentrated sulfuric acid, polyphosphoric acid, phosphorus pentoxide, boron trifluoride, zinc chloride and so on. However, in availability from commercial sources, acetic anhydride is particularly suitable. When acetic anhydride is used as said dehydrative condensing agent, it is preferable to use not less than 1 mol of acetic anhydride per mol of the ethylene compound. Needless to say there is no upper limit to the proportion of acetic anhydride that may be used but from economic points of view the use of 1-5 molar equivalents is preferred and when an inert solvent such as toluene is used in combination, 1-2 molar equivalents are sufficient. The reaction temperature is preferably 30°-120° C. and, for still better results, 40°-80° C. If the reaction temperature exceeds 120° C., the amounts of byproducts tend to be increased. On the other hand, the reaction time tends to be protracted when the reaction temperature is below 30° C. There is virtually no restriction on reaction time but the reaction generally goes to completion in several hours. 
     For undeterred progress of this reaction, it is preferable to use an inert solvent, such as toluene or dichloroethane, in conjunction. When the dehydrative condensing agent is acetic anhydride, toluene is a preferred inert solvent from the standpoint of work-ability. 
     After completion of the reaction, the reaction mixture is treated with alkali, for example an aqueous solution of sodium hydroxide, and extracted with an organic solvent such as toluene for purification. From workability points of view, it is good practice to carry out the alkali treatment in the presence of an organic solvent. 
     The organic extract is washed with hot water and the organic layer is concentrated, preferably followed by stirring with methanol under reflux and subsequent cooling, to provide the phthalide compound. The phthalide compound can also be obtained by subjecting said organic extract to a conventional purification procedure, for example column chromatography, and, if necessary, further to the same methanol treatment as above. 
     The compound of this invention is a useful color former for recording material in that it is either white or of pale color, absorbing little the visible and near infrared regions of the spectrum. However, when reacted with a developer, the compound shows an intense absorption in the near infrared region of 680-750 nm and, yet, absorbs little visible light. Therefore, the near infrared absorber produced by the reaction between this compound and a developer is either colorless or of pale color to the eye and has the characteristic that, in the case of a recording material, the recorded image can hardly be recognized by the eye but can be read with the aid of an OCR using a light source with an emission band of 650-750 nm. Furthermore, when this compound is used in combination with other color formers, desired shades dependent on the concomitant color formers can be obtained. 
     The phthalide compound of this invention is characterized in that ring A in general formula (I) has any of the substituents mentioned hereinbefore. Recording materials containing known phthalide compounds (for example the aforementioned Compounds A-D) as described in inter alia U.S. Pat. No. 4,119,776, wherein this particular moiety is constituted by p-aminophenyl provide developed images that absorb the visible region as well and show colors in the blue-green series. 
     Specific examples of the compound of this invention are shown in Table 1. 
     
                                           TABLE 1                                 
__________________________________________________________________________
 ##STR12##                                                                
              Position                                                    
        R.sub.1                                                           
            n of R.sub.1                                                  
                   R.sub.2                                                
                         R.sub.3                                          
                             R.sub.4                                      
                                   R.sub.5                                
                                      R.sub.6                             
                                          Ring B                          
__________________________________________________________________________
Compound 1                                                                
        Me  1 4-   Me    Et  Et    Et H   Bz                              
Compound 2                                                                
        Et  1 4-   Me    Et  Et    Et H   Bz                              
Compound 3                                                                
        n-Bu                                                              
            1 4-   Me    Et  Et    Et H   Bz                              
Compound 4                                                                
        n-Oc                                                              
            1 4-   Me    Et  Et    Et H   Bz                              
Compound 5                                                                
        Me  1 4-   Me    Et  Et    Et Me  Bz                              
Compound 6                                                                
        H          Me    Et  n-Bu  n-Bu                                   
                                      Et  Bz                              
Compound 7                                                                
        n-Oc                                                              
            1 4-   Me    Et  Et    Et Me  Bz                              
Compound 8                                                                
        Me  1 4-   Me    Et  Me    Me H   Bz                              
Compound 9                                                                
        H          Me    Et  Me    Me Me  Bz                              
Compound 10                                                               
        n-Bu                                                              
            1 4-   Me    Et  Me    Me H   Bz                              
Compound 11                                                               
        n-Oc                                                              
            1 4-   Me    Et  Me    Me H   Bz                              
Compound 12                                                               
        Me  1 4-   Me    Et  Me    Me Me  Bz                              
Compound 13                                                               
        H          Me    Et  Me    Me H   Bz                              
Compound 14                                                               
        H          Me    Et  n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 15                                                               
        n-Bu                                                              
            1 4-   Me    Et  n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 16                                                               
        Me  1 4-   Me    n-Bu                                             
                             Et    Et H   Bz                              
Compound 17                                                               
        H          Me    n-Bu                                             
                             Et    Et H   Bz                              
Compound 18                                                               
        n-Oc                                                              
            1 4-   Me    n-Bu                                             
                             Et    Et Me  Bz                              
Compound 19                                                               
        n-Bu                                                              
            1 4-   Me    n-Bu                                             
                             Me    Me H   Bz                              
Compound 20                                                               
        H          Me    n-Bu                                             
                             Me    Me H   Bz                              
Compound 21                                                               
        Me  1 4-   Me    n-Bu                                             
                             Me    Me Me  Bz                              
Compound 22                                                               
        H          Me    n-Bu                                             
                             Me    Me Me  Bz                              
Compound 23                                                               
        n-Bu                                                              
            1 4-   Me    n-Bu                                             
                             n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 24                                                               
        H          Me    n-Bu                                             
                             n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 25                                                               
        H          Me    n-Bu                                             
                             n-Bu  n-Bu                                   
                                      Me  Bz                              
Compound 26                                                               
        Me  1 4-   Me    n-Oc                                             
                             Et    Et H   Bz                              
Compound 27                                                               
        H          Me    n-Oc                                             
                             Et    Et Me  Bz                              
Compound 28                                                               
        n-Bu                                                              
            1 4-   Me    n-Oc                                             
                             Me    Me H   Bz                              
Compound 29                                                               
        H          Me    n-Oc                                             
                             Me    Me H   Bz                              
Compound 30                                                               
        H          Me    n-Oc                                             
                             Me    Me Me  Bz                              
Compound 31                                                               
        n-Oc                                                              
            1 4-   Me    n-Oc                                             
                             n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 32                                                               
        H          Me    n-Oc                                             
                             n-Bu  n-Bu                                   
                                      Me  Bz                              
Compound 33                                                               
        Me  1 4-   Ph    Et  Et    Et H   Bz                              
Compound 34                                                               
        H          Ph    Et  Et    Et H   Bz                              
Compound 35                                                               
        n-Bu                                                              
            1 4-   Ph    Et  Et    Et H   Bz                              
Compound 36                                                               
        n-Oc                                                              
            1 4-   Ph    Et  Et    Et H   Bz                              
Compound 37                                                               
        Me  1 4-   Ph    Et  Et    Et Me  Bz                              
Compound 38                                                               
        H          Ph    Et  Et    Et Me  Bz                              
Compound 39                                                               
        n-Oc                                                              
            1 4-   Ph    Et  Et    Et Me  Bz                              
Compound 40                                                               
        Me  1 4-   Ph    Et  Me    Me H   Bz                              
Compound 41                                                               
        H          Ph    Et  Me    Me H   Bz                              
Compound 42                                                               
        n-Bu                                                              
            1 4-   Ph    Et  Me    Me H   Bz                              
Compound 43                                                               
        n-Oc                                                              
            1 4-   Ph    Et  Me    Me H   Bz                              
Compound 44                                                               
        Me  1 4-   Ph    Et  Me    Me Me  Bz                              
Compound 45                                                               
        H          Ph    Et  Me    Me Me  Bz                              
Compound 46                                                               
        H          Ph    Et  n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 47                                                               
        H          Ph    n-Bu                                             
                             Et    Et H   Bz                              
Compound 48                                                               
        n-Oc                                                              
            1 4-   Ph    n-Bu                                             
                             Et    Et Me  Bz                              
Compound 49                                                               
        n-Bu                                                              
            1 4-   Ph    n-Bu                                             
                             Me    Me H   Bz                              
Compound 50                                                               
        Me  1 4-   Ph    n-Bu                                             
                             Me    Me Me  Bz                              
Compound 51                                                               
        H          Ph    n-Bu                                             
                             n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 52                                                               
        H          Ph    n-Bu                                             
                             n-Bu  n-Bu                                   
                                      Me  Bz                              
Compound 53                                                               
        H          Ph    Et  Me    Me n-Bu                                
                                          Bz                              
Compound 54                                                               
        H          Ph    n-Oc                                             
                             Me    Me H   Bz                              
Compound 55                                                               
        H          Ph    n-Oc                                             
                             Me    Me Me  Bz                              
Compound 56                                                               
        H          Ph    n-Oc                                             
                             n-Bu  n-Bu                                   
                                      Me  Bz                              
Compound 57                                                               
        H          Me    Et  Et    Et H   Bz                              
Compound 58                                                               
        H          Et    Et  Et    Et H   Bz                              
Compound 59                                                               
        n-Pr                                                              
            1 4-   Me    Me  Et    Et H   Bz                              
Compound 60                                                               
        n-Oc                                                              
            1 4-   Me    Et  n-Pr  n-Pr                                   
                                      H   Bz                              
Compound 61                                                               
        Me  1 4-   Et    Et  Et    Et Et  Bz                              
Compound 62                                                               
        H          Me    Et  Et    Et n-Bu                                
                                          Bz                              
Compound 63                                                               
        n-Oc                                                              
            1 4-   Me    Me  Et    Et Me  Bz                              
Compound 64                                                               
        Me  1 4-   Et    n-Pr                                             
                             Me    Me H   Bz                              
Compound 65                                                               
        H          n-Bu  Me  n-Pr  n-Pr                                   
                                      H   Bz                              
Compound 66                                                               
        n-Bu                                                              
            1 4-   p-tol Et  Me    Me H   Bz                              
Compound 67                                                               
        n-Pr                                                              
            1 4-   Me    Et  n-He  n-He                                   
                                      H   Bz                              
Compound 68                                                               
        Me  1 4-   Me    n-Pr                                             
                             Me    Me Me  Bz                              
Compound 69                                                               
        H          n-Pr  n-He                                             
                             Me    Me Me  Bz                              
Compound 70                                                               
        H          Me    Et  Et    Et Me  Bz                              
Compound 70                                                               
        n-Bu                                                              
            1 4-   p-tol Et  n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 72                                                               
        Me  1 4-   Ph    Et  Et    Me H   Bz                              
Compound 73                                                               
        H          Ph    Et  Et    Me H   Bz                              
Compound 74                                                               
        n-Bu                                                              
            1 4-   Ph    Et  n-Pr  Et H   Bz                              
Compound 75                                                               
        n-Oc                                                              
            1 4-   Ph    Et  Et    Et Et  Bz                              
Compound 76                                                               
        Me  1 4-   p-tol Et  Et    Et Me  Bz                              
Compound 77                                                               
        Et  1 4-   p-ClPh                                                 
                         Me  Et    Et n-Bu                                
                                          Bz                              
Compound 78                                                               
        n-Pr                                                              
            1 4-   Ph    Et  Et    Me Me  Bz                              
Compound 79                                                               
        Me  1 4-   p-tol Et  Me    Me H   Bz                              
Compound 80                                                               
        H          Ph    Me  n-He  n-He                                   
                                      H   Bz                              
Compound 81                                                               
        n-Bu                                                              
            1 4-   Et    Et  n-Pr  n-Pr                                   
                                      H   Bz                              
Compound 82                                                               
        n-Pr                                                              
            1 4-   Et    Et  Me    Me H   Bz                              
Compound 83                                                               
        Me  1 4-   Ph    n-He                                             
                             Me    Me Me  Bz                              
Compound 84                                                               
        H          Ph    n-Oc                                             
                             Et    Et H   Bz                              
Compound 85                                                               
        H          Ph    n-Pr                                             
                             n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 86                                                               
        H          p-tol Et  Et    Et MeO Bz                              
Compound 87                                                               
        Me  1 4-   Me    Et  n-Bu  n-Bu                                   
                                      EtO Bz                              
Compound 88                                                               
        2-EtHe                                                            
            1 4-   Et    Me  p-ClPh                                       
                                   Et n-OcO                               
                                          Bz                              
Compound 89                                                               
        Me  1 4-   Me    Et  Et    Et n-BuO                               
                                          Bz                              
Compound 90                                                               
        n-Pr                                                              
            1 4-   i-Pr  n-He                                             
                             Ph    Ph Me  Bz                              
Compound 91                                                               
        H          Me    Et  p-EtOPh                                      
                                   Et H   Bz                              
Compound 92                                                               
        Me  1 2-   Me    Et  Et    Et H   Bz                              
Compound 93                                                               
        i-Bu                                                              
            1 2-   n-Bu  Et  p-tol Et n-BuO                               
                                          Bz                              
Compound 94                                                               
        n-Pe                                                              
            1 2-   Me    Et  n-Bu  n-Bu                                   
                                      EtO Bz                              
Compound 95                                                               
        n-Pr                                                              
            1 2-   Ph    Me  n-Pe  n-Pe                                   
                                      Et  Bz                              
Compound 96                                                               
        s-Bu                                                              
            1 3-   m-tol Et  Ph    Me MeO Bz                              
Compound 97                                                               
        Me  1 3-   Me    Et  Et    Et H   Bz                              
Compound 98                                                               
        MeO 1 4-   Me    Et  Et    Et H   Bz                              
Compound 99                                                               
        MeO 1 4-   Ph    n-Bu                                             
                             p-MeOPh                                      
                                   Et MeO Bz                              
Compound 100                                                              
        EtO 1 4-   Me    n-Oc                                             
                             Ph    Et n-OcO                               
                                          Bz                              
Compound 101                                                              
        EtO 1 4-   Me    Et  n-Oc  n-Oc                                   
                                      n-Bu                                
                                          Bz                              
Compound 102                                                              
        n-PrO                                                             
            1 4-   Et    n-He                                             
                             i-Pr  n-Bu                                   
                                      n-BuO                               
                                          Bz                              
Compound 103                                                              
        n-BuO                                                             
            1 4-   Ph    n-Pr                                             
                             Me    i-Bu                                   
                                      n-Bu                                
                                          Bz                              
Compound 104                                                              
        i-PrO                                                             
            1 2-   n-Bu  Et  o-tol Me H   Bz                              
Compound 105                                                              
        i-BuO                                                             
            1 2-   Me    Et  n-Pr  Me EtO Bz                              
Compound 106                                                              
        MeO 1 3-   Me    n-Do                                             
                             m-tol Et n-Bu                                
                                          Bz                              
Compound 107                                                              
        EtO 1 3-   Me    Et  Me    Me n-HeO                               
                                          Bz                              
Compound 108                                                              
        Cl  1 4-   Me    Et  Et    Et H   Bz                              
Compound 109                                                              
        Cl  1 4-   m-ClPh                                                 
                         n-Hp                                             
                             Me    Me i-BuO                               
                                          Bz                              
Compound 110                                                              
        Cl  1 4-   n-Pr  n-Pe                                             
                             Ph    Me Et  Bz                              
Compound 111                                                              
        Cl  1 2-   Me    n-De                                             
                             n-Bu  n-Bu                                   
                                      EtO Bz                              
Compound 112                                                              
        Cl  1 2-   Ph    Et  Ph    Me H   Bz                              
Compound 113                                                              
        Br  1 4-   n-Bu  Me  Et    Me n-Bu                                
                                          Bz                              
Compound 114                                                              
        Br  1 4-   Me    Et  p-tol Et MeO Bz                              
Compound 115                                                              
        Br  1 2-   n-Bu  2-EtHe                                           
                             Et    Me n-HpO                               
                                          Bz                              
Compound 116                                                              
        F   1 4-   Me    i-Bu                                             
                             Me    Me Me  Bz                              
Compound 117                                                              
        F   1 4-   Ph    Et  p-ClPh                                       
                                   Et H   Bz                              
Compound 118                                                              
        F   1 2-   Me    Et  Et    Et n-BuO                               
                                          Bz                              
Compound 119                                                              
        Me  2 2,3- Et    Me  Et    Et H   Bz                              
Compound 120                                                              
        Me  2 2,4- Ph    Me  Me    Me EtO Bz                              
Compound 121                                                              
        Me  2 2,4- Me    Et  Et    Et H   Bz                              
Compound 122                                                              
        Me  2 2,5- Ph    Me  Me    Me n-Bu                                
                                          Bz                              
Compound 123                                                              
        Me  3 2,4,6-                                                      
                   Me    Et  p-tol Et n-OcO                               
                                          Bz                              
Compound 124                                                              
        Me  3 2,3,4-                                                      
                   Me    Et  Et    Et MeO Bz                              
Compound 125                                                              
        Me  2 3,5- n-Pr  Et  Me    Ph Et  Bz                              
Compound 126                                                              
        Et  2 2,4- Me    Et  Me    Me H   Bz                              
Compound 127                                                              
        Et  2 2,5- Et    Me  p-MeOPh                                      
                                   Me Me  Bz                              
Compound 128                                                              
        MeO 3 2,4,6-                                                      
                   Me    Et  Et    Et n-PeO                               
                                          Bz                              
Compound 129                                                              
        MeO 2 2,5- p-tol Et  Me    Me H   Bz                              
Compound 130                                                              
        MeO 2 3,4- Me    Et  Ph    Ph n-BuO                               
                                          Bz                              
Compound 131                                                              
        MeO 2 3,5- n-Bu  Et  Et    s-Bu                                   
                                      Et  Bz                              
Compound 132                                                              
        EtO 2 2,4- Ph    Me  n-Bu  n-Bu                                   
                                      n-Heo                               
                                          Bz                              
Compound 133                                                              
        Cl  2 2,4- Me    Et  Et    Et H   Bz                              
Compound 134                                                              
        Cl  3 2,4,6-                                                      
                   Me    Me  p-ClPh                                       
                                   Et EtO Bz                              
Compound 135                                                              
        Cl  2 2,5- Me    Et  Ph    Ph H   Bz                              
Compound 136                                                              
        Cl  3 2,3,4-                                                      
                   n-Bu  Et  Et    Et Me  Bz                              
Compound 137                                                              
        Cl  2 3,5- Ph    Me  Et    Et i-PrO                               
                                          Bz                              
Compound 138                                                              
        Br  2 2,4- n-Bu  Me  n-Bu  n-Bu                                   
                                      H   Bz                              
Compound 139                                                              
        Br  3 2,3,4-                                                      
                   p-tol n-Pr                                             
                             Me    Me Me  Bz                              
Compound 140                                                              
        Br  2 2,5- Me    Et  Et    Et MeO Bz                              
Compound 141                                                              
        F   2 2,4- n-Bu  Et  p-EtOPh                                      
                                   Et H   Bz                              
Compound 142                                                              
        F   2 2,5- Ph    Et  Et    Et MeO Bz                              
Compound 143                                                              
        H          Ph    Et  Me    Me n-Bu                                
                                          Np                              
Compound 144                                                              
        Me  1 4-   Me    Et  Et    Et H   Np                              
Compound 145                                                              
        n-Pr                                                              
            1 4-   Me    Et  n-Bu  Et EtO Np                              
Compound 146                                                              
        MeO 1 4-   Me    Et  n-Bu  n-Bu                                   
                                      MeO Np                              
Compound 147                                                              
        n-BuO                                                             
            1 4-   n-Bu  Me  Me    Me H   Np                              
Compound 148                                                              
        Et  1 2-   Ph    Et  Et    Et H   Np                              
Compound 149                                                              
        Cl  1 4-   Me    Et  n-Bu  Et EtO Np                              
Compound 150                                                              
        Me  2 2,4- Me    Et  Ph    Et Me  Np                              
Compound 151                                                              
        MeO 2 3,4- Ph    n-Bu                                             
                             Me    Me H   Np                              
Compound 152                                                              
        Cl  3 2,3,4-                                                      
                   p-tol Et  Ph    Et n-PrO                               
                                          Np                              
Compound 153                                                              
        H          Me    Et  Me    Me Me  TcBz                            
Compound 154                                                              
        H          Ph    Et  Me    Me MeO TcBz                            
Compound 155                                                              
        Me  1 4-   Me    Et  Et    Et H   TcBz                            
Compound 156                                                              
        Me  1 2-   Me    Et  Et    Et H   TcBz                            
Compound 157                                                              
        n-Bu                                                              
            1 3-   Et    Et  p-ClPh                                       
                                   Et Et  TcBz                            
Compound 158                                                              
        MeO 1 4-   Me    n-Bu                                             
                             n-Pr  Me H   TcBz                            
Compound 159                                                              
        EtO 1 4-   Ph    n-Bu                                             
                             Ph    Me n-PrO                               
                                          TcBz                            
Compound 160                                                              
        Cl  1 4-   Me    Et  Me    Me MeO TcBz                            
Compound 161                                                              
        Br  1 4-   p-tol Et  Me    Me H   TcBz                            
Compound 162                                                              
        Me  3 2,4,6-                                                      
                   Me    Et  Me    Me n-BuO                               
                                          TcBz                            
Compound 163                                                              
        MeO 2 3,4- Me    Me  Et    Et Me  TcBz                            
Compound 164                                                              
        Cl  2 2,4- Me    Me  Ph    Ph H   TcBz                            
__________________________________________________________________________
 ##STR13##                                                                
            R.sub.2                                                       
                  R.sub.3                                                 
                       R.sub.4                                            
                            R.sub.5                                       
                                 R.sub.6                                  
                                        Ring B                            
__________________________________________________________________________
Compound 165                                                              
            Me    Et   Et   Et   H      Bz                                
Compound 166                                                              
            Ph    Et   Me   Me   Me     Bz                                
Compound 167                                                              
            Et    Me   Ph   Et   Eto    Bz                                
Compound 168                                                              
            Me    Et   n-Pr Et   n-BuO  Bz                                
Compound 169                                                              
            p-tol n-Bu n-Bu Et   n-PeO  Bz                                
Compound 170                                                              
            n-Bu  n-He Ph   Ph   n-Bu   Bz                                
Compound 171                                                              
            p-tol Et   Ph   Ph   MeO    Np                                
Compound 172                                                              
            Me    n-Bu Me   Me   Et     Np                                
Compound 173                                                              
            Me    Me   Et   Et   n-BuO  N                                 
Compound 174                                                              
            Ph    Et   Ph   Et   H      Np                                
Compound 175                                                              
            Me    Et   Et   Et   H      TcBz                              
Compound 176                                                              
            Me    Et   n-Bu Et   EtO    TcBz                              
Compound 177                                                              
            Me    n-Bu Ph   Et   Me     TcBz                              
Compound 178                                                              
            Ph    Et   Ph   Ph   i-PrO  TcBz                              
__________________________________________________________________________
 ##STR14##                                                                
            R.sub.2                                                       
                  R.sub.3                                                 
                       R.sub.4                                            
                            R.sub.5                                       
                                 R.sub.6                                  
                                        Ring B                            
__________________________________________________________________________
Compound 179                                                              
            Me    Et   Et   Et   H      Bz                                
Compound 180                                                              
            Ph    Et   n-Bu Me   MeO    Bz                                
Compound 181                                                              
            Et    Me   Et   Et   Et     Bz                                
Compound 182                                                              
            Me    Et   Ph   Et   EtO    Bz                                
Compound 183                                                              
            p-tol n-Bu Ph   Ph   H      Bz                                
Compound 184                                                              
            Me    Et   n-Pr Et   Me     Np                                
Compound 185                                                              
            Me    Et   Et   Et   MeO    Np                                
Compound 186                                                              
            Ph    Et   Ph   Et   Me     Np                                
Compound 187                                                              
            n-Bu  n-Bu Ph   Ph   H      Np                                
Compound 188                                                              
            n-Bu  Et   n-Bu Et   n-BuO  TcBz                              
Compound 189                                                              
            Ph    n-Pr Me   Me   H      TcBz                              
Compound 190                                                              
            Me    Et   Ph   Ph   n-OcO  TcBz                              
Compound 191                                                              
            Me    Et   Ph   Et   Me     TcBz                              
__________________________________________________________________________
 
    
     In the table, H stands for hydrogen; Me for methyl, Et for ethyl, n-Pr for n-propyl, i-Pr for isopropyl, n-Bu for n-butyl, i-Bu for isobutyl, s-Bu for sec-butyl, n-Pe for n-pentyl, n-He for n-hexyl, n-Hp for n-heptyl, n-Oc for n-octyl, 2-EtHe for 2-ethylhexyl, n-De for n-decyl, n-Do for n-dodecyl, Ph for phenyl, p-tol for p-tolyl, o-tol for o-tolyl, m-tol for m-tolyl, p-ClPh for p-chlorophenyl, m-C 1  Ph for m-chlorophenyl, p-MeOPh for p-methoxyphenyl, p-EtOPh for p-ethoxyphenyl, MeO for methoxy, EtO for ethoxy, n-PrO for n-propoxyl, i-PrO for isopropoxy, n-BuO for n-butoxy, i-BuO for isobutoxy, n-PeO for n-pentyloxy, n-HeO for n-hexyloxyl, n-HpO for n-heptyloxy, n-OcO for n-octyloxy, Cl for chlorine, Br for bromine, F for fluorine ##STR15## 
     It is considered that the near infrared absorber of this invention is an electron transfer reaction product between the color former and a developer and, on account of this reaction, absorbs the near infrared region. Generally, it can be produced by dissolving the color former and developer in a solvent and distilling off the solvent. In its application, the above solution may be coated on a support, e.g. a sheet of wood-free paper or synthetic paper or a plastic film, and dried to provide the desired near infrared absorber on the support. In some cases, the absorber can be manufactured by melting the color former and developer under heating and cooling the melt. 
     The developer that can be used in the near infrared absorber includes, among others, phenol derivatives, acidic polymers, metal modification products thereof, organic carboxylic acids and metal salts thereof. 
     The following are some examples of developers. 
     Phenol derivatives: 4-tert-butylphenol, 4-octylphenol, 4-phenylphenol, 1-naphthol, 2-naphthol, hydroquinone, resorcinol, 4-tert-octylcatechol, 2,2&#39;-dihydroxybiphenyl, 4,4&#39;-dihydroxydiphenyl ether, 2,2-bis(4-hydroxyphenyl)propane [generic name: bisphenol A], tetrabromobisphenol A, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 1,4-bis(4-hydroxycumyl)benzene, 1,3,5-tris(4-hydroxycumyl)benzene, 4,4&#39;-(m-phenylenediisopropylidene)bisphenol, 4,4&#39;-(p-phenylenediisopropylidene)bisphenol, ethyl bis(4-hydroxyphenyl)acetate, n-butyl 4,4-bis(4-hydroxyphenyl)valerate, benzyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 2-phenoxyethyl 2,4-dihydroxybenzoate, dimethyl 4-hydroxyphthalate, n-propyl gallate, n-octyl gallate, n-dodecyl gallate, n-octadecyl gallate, hydroquinone monobenzyl ether, bis(3-methyl-4-hydroxyphenyl)sulfide, bis(2-methyl-4-hydroxyphenyl)suflide, bis(3-phenyl-4-hydroxyphenyl)suflide, bis(3-cyclohexyl-4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfone [generaic name bisphenol S], tetrabromobisphenol S, bis(3-allyl-4-hydroxyphenyl)suflone, 2,4&#39;-dihydroxydiphenyl sulfone, 4-hydroxy-4&#39;-methyldiphenyl sulfone, 4-hydroxy-4&#39;-chlorodiphenyl sulfone, 4-hydroxy-4&#39;-n-propoxydiphenyl sulfone, 4-hydroxy-4&#39;-isopropoxydiphenyl sulfone, 4-hydroxy-4&#39;-n-butoxydiphenyl sulfone, 3,4-dihydroxy-4&#39;-methyldiphenyl sulfone, 2,4-dihydroxydiphenyl sulfone, 2-methoxy-4&#39;-hydroxydiphenyl sulfone, 2-ethoxy-4&#39;-hydroxydiphenyl sulfone, bis(2-hydroxy-5-tert-butylphenyl)sulfone, bis(2-hydroxy-5-chlorophenyl)sulfone, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane, 1,5-bis(4-hydroxyphenylthio)-3-oxapentane and so on. 
     The acidic polymer or its metal modification product includes phenol resin, alkylphenol resin, maleic acid resin, phenol-acetylene resin, phenol-formaldehyde resin, products of condensation of carboxylic acids containing at least one hydroxyl group with formaldehyde, and modification products thereof with polyvalent metals such as zinc, nickel, etc., among others. 
     The organic carboxylic acid or its metal salt includes various organic acids such as salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-(α-methylbenzyl)salicylic acid, 4-(3-p-toluenesulfonylpropyloxy)salicylic acid, 5-{p-[2-(p-methoxyphenoxy)ethoxy]cumyl}salicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-methyl-5-α-methylbenzylsalicylic acid, 4-[2-(4-methoxyphenoxy)ethoxy]salicylic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-6-naphthoic acid, monobenzyl phthalate, monophenyl phthalate, 4-nitrobenzoic acid, 3-nitrobenzoic acid, 2-nitrobenzoic acid and 4-chlorobenzoic acid or their salts with various metals (e.g. nickel, zinc, aluminum, calcium, etc.) and complexes such as zinc thiocyanate antipyrine complex, molybdic acid acetylacetone complex, etc., among others. 
     Aside from the above compounds, the known developers for color-forming recording materials, e.g. urea derivatives such as phenylthiourea, and inorganic developers such as clay can also be employed as well. 
     Among the particularly preferred developers, the preferred phenol derivative includes bisphenol A, bisphenol S, benzyl p-hydroxybenzoate, 2,2-bis(p-hydroxyphenyl)-4-methylpentane, 3,3&#39;-diallyl-4,4&#39;-dihydroxydiphenyl sulfone, 1,1-bis(p-hydroxyphenyl)cyclohexane, 1,5-bis(p-hydroxyphenylmercapto)-3-oxapentane, 4-hydroxy-4&#39;-isopropoxydiphenyl sulfone, 3,4-dihydroxy-4&#39;-methyldiphenyl sulfone, 1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane, tetrabromobisphenol A and tetrabromobisphenol S, among others. 
     The preferred acidic polymer or its metal modification product includes zinc-modified p-octylphenolformaldehyde resin, p-phenylphenol resin and p-alkyl-phenol-formaldehyde resin (e.g. known under the tradenames of Tamanol and Hitanol), among others. 
     The preferred organic carboxylic acid or its metal salt includes salicylic acid derivative zinc salts such as zinc 4-[2-(4-methoxyphenoxy)ethoxy]salicylate, among others. 
     The ratio of the compound of this invention to the developer varies with different species of the compound but may generally be about 10:90-75:25 and preferably about 20:80-50:50. 
     The near infrared absorber of this invention can be put to use as it is or in the form of a near infrared absorbing composition containing a binder and other additives, for example by such techniques as coating, compounding, or hard-coating on or with such matrices as paper, plastic sheet, plastic film, glass, clear resin, etc. or polymerizing with monomers, in such applications as near infrared absorbing filters, optical recording media, protective goggles, agricultural film, heat rays absorbing glass, filters for light-receiving devices and so forth. 
     The phthalide compound of this invention can be used in secret ink, in which application the characters or codes written or printed are not visible to the eye but can be read with the OCR or equivalent. As for secret ink, an oil-based secret ink can be produced by, for example, dissolving the phthalide compound of this invention and a developer in an oily vehicle, if necessary followed by adding an oil-soluble binder resin or the like. A water-based ink for secret pen writing can be produced by, for example, dispersing the near infrared absorber containing both the compound of this invention and a developer in a water-soluble organic solvent such as alcohol and, then, adding water, if necessary together with a water-soluble binder resin or the like. 
     In the production of said oil-based secret ink, the vehicle can be an ordinary organic solvent such as aromatic hydrocarbons, e.g. toluene and xylene, methyl ethyl ketone and so on. However, in the production of writing utensils (felt pen, ball-point pen, etc.), it is advantages, from the standpoint of health protection and safety, to employ an aliphatic or alicyclic hydrocarbon solvent boiling at 75°-180° C. The alicyclic hydrocarbon solvent mentioned just above includes dimethylcyclohexane, ethylcyclohexane, propylcyclohexane, butylcyclohexane, cyclohexene, etc., and the aliphatic hydrocarbon solvent includes saturated aliphatic hydrocarbons such as n-hexane, n-octane, isooctane, etc. and petroleum-based mixture solvents such as ligroin, mineral spirit, purified rubber oil, and so on. 
     For the production of a water-based ink, an alcohol or an aqueous solution of a low-volatile or non-volatile hydrophilic organic solvent can be used with advantage as a dispersant. The alcohol mentioned above preferably includes lower alcohols such as methanol, ethanol, isopropyl alcohol, etc., while the preferred aqueous solution of low-volatile or non-volatile hydrophilic organic solvent includes aqueous solutions prepared by dissolving 5-200 parts of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, glycerol, diglycerol, methylcarbitol, ethylcarbitol, butylcarbitol, ethylcellosolve, butylcellosolve or the like in each 100 parts of water. 
     If necessary, a variety of water-soluble resins (for a water-based secret ink) and solvent-soluble resins (for an oil-based secret ink) can be used as the dispersant, binder and/or thickener. 
     Among the solvent-soluble resins mentioned above can be reckoned hydrogenated rosin and rosin ester resin, alkylphenol resin, polyolefin resin, rosin-modified alkyd resin, ketone resin and so on. 
     Among the water-soluble resins can be reckoned melamine-formaldehyde polymer, water-soluble acrylic resin, ligninsulfonic acid, etc., while the water-dispersible resin may for example be polyvinyl butyral, styrene-butadiene copolymer or the like. 
     The preferred formulation per 100 parts of ink is 5-20 parts of the compound of this invention, 10-30 parts of developer, 5-20 parts of resin and 40-80 parts of solvent. 
     In a recording material utilizing the reaction between a color former and a developer, the compound of this invention can be used singly in the recording material or, if necessary, can be used in combination with one or more different coloring materials (color former). Particularly, a black colored image can be obtained by using one or more species of the compound of this invention in combination with one or more species of the fluorane compound of general formula (IV) ##STR16## wherein R 7  and R 8  independently represent alkyl, alkoxyalkyl, cycloalkyl, aryl or tetrahydrofuryl; R 9  represents hydrogen, methyl or chlorine; R 10  and R 11  independently represent hydrogen, alkyl, chlorine or fluorine; R 7  and R 8  may, taken together with the adjacent nitrogen atom, form a heterocyclic group. 
     The following is a partial listing of species of the fluorane compound of general formula (IV) which can be used in this invention. 
     2-Anilino-3-methyl-6-dimethylaminofluorane, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-di-n-propylaminofluorane, 2-anilino-3-methyl-6-di-n-butylaminofluorane, 2-anilino-3-methyl-6-di-n-pentylaminofluorane, 2-anilino-3-methyl-6-(N-methyl-N-ethylamino)fluorane, 2-anilino-3-methyl-6-(N-methyl-N-n-propylamino)fluorane, 2-anilino-3-methyl-6-(N-methyl-N-n-butylamino)fluorane, 2-anilino-3-methyl-6-(N-methyl-N-isobutylamino)fluorane, 2-anilino-3-methyl-6-(N-methyl-N-n-pentylamino)fluorane, 2-anilino-3-methyl-6-(N-methyl-N-cyclohexylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-n-propylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-n-butylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-isobutylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-n-pentylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-isopentylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-n-octylamino)fluorane, 2-anilino-3-methyl-6-[N-ethyl-N-(3-ethoxypropyl)amino]fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-p-tolylamino)fluorane, 2-anilino-3-methyl-6-(N-ethyl-N-tetrahydrofrufurylamino)fluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2-(2-chloroanilino)-6-diethylaminofluorane, 2-(2-chloroanilino)-6-di-n-butylaminofluorane, 2-(2-fluoroanilino)-6-diethylaminofluorane, 2-(3-trifluoromethylanilino)-6-diethylaminofluorane, 2-(3-methylanilino)-3-methyl-6-diethylaminofluorane, 2-(4-methylanilino)-3-methyl-6-diethylaminofluorane, 2-(4-tertpentylanilino)-3-methyl-6-diethylaminofluorane, 2-(3-chloro-4-methylanilino)-3-methyl-6-diethylaminofluorane, 2-(2,4-dimethylanilino)-3-methyl-6-diethylaminofluorane, 2-(2,6-dimethylanilino)-3-methyl-6-diethylaminofluorane, 2-(2,6-diethylanilino)-3-methyl-6-diethylaminofluorane, 2-(2,4-dimethylanilino)-3-methyl-6-di-n-butylaminofluorane, 2-(2,6-dimethylanilino)-3-methyl-6-di-n-butylaminofluorane and 2-(2,6-diethylanilino)-3-methyl-6-di-n-butylaminofluorane, among others. 
     In addition with the combined use of the compound of this invention and the fluorane compound of general formula (IV), other color formers that are conventionally used in recording materials of this type can be selectively used as required for the purpose of adjusting the developed color or absorption characteristics. 
     The diaryl phthalide compound, among said other color formers, includes 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide (generic name CVL), 3,3-bis(4-dimethylaminophenyl)phthalide, 3-(4-dimethylaminophenyl)-3-(4-diethylamino-2-methylphenyl)-6dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6-dimetylaminophthalide and 3-(4-dimethylaminophenyl)-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, among others. 
     The indolyl phthalide compound, among said other color formers, includes 3-(4-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-n-octyl-2-methylindol-3-yl)phthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3-(2-ethoxy-4-dibutylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide and 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-octyl-2-methylindol-3-yl)phthalide, among others. 
     The vinyl phthalide compound includes 3-(4-diethylaminophenyl)-3-[2,2-bis(1-ethyl-2-methylindol-3-yl)ethenyl]phthalide, 3,3-bis[2-(4-dimethylaminophenyl)-2-(4-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[2-(4-pyrrolidinophenyl)-2-(4-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[2,2-bis(4-dimethylaminophenyl)ethenyl]-4,5,6,7-tetrachlorophthalide and 3,3-bis[2,2-bis(4-pyrrolidinophenyl)ethenyl]-4,5,6,7-tetrabromophthalide, among others. 
     The azaphthalide compound includes 3,3-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-[4-(N-ethyl-N-phenylamino)-2-ethoxyphenyl]-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide and 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-n-octyl-2-methylindol-3-yl)-4-azaphthalide, among others. 
     The diarylmethane compound includes 4,4&#39;-bis(dimethylamino)benzhydryl benzyl ether and N-halophenylleucauramine, among others. 
     The rhodamine lactam compound includes rhodamine B anilinolactam, rhodamine B (4-nitroanilino)lactam and rhodamine B (4-chloroanilino)lactam, among others. 
     The thiazine compound includes benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue, among others. 
     The spiropyran compound includes 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3-phenylspirodinaphthopyran, 3-benzylspirodinaphthopyran and 3-propylspirodibenzopyran, among others. 
     The fluorene compound includes 3,6-bis(dimethylamino)fluorenespiro[9,3&#39;]-6&#39;-dimethylaminophthalide, 3-diethylamino-6-(N-allyl-N-methylamino)fluorenespiro[9,3&#39;]-6&#39;-dimethylaminophthalide, 3,6-bis(dimethylamino)-spiro[fluorene-9,6&#39;-6&#39;H-chromeno(4,3-b)indole], 3,6-bis(dimethylamino)-3&#39;-methylspiro[fluorene-9,6&#39;-6&#39;H-chromeno(4,3-b)indole], 3,6-bis(diethylamino)-3&#39;-methyl-spiro[fluorene-9,6&#39;-6&#39;-H-chromeno(4,3-b)indole], among others. 
     These color formers can be used singly or in combination. 
     When the compound of this invention is used in combination with a fluorane compound of general formula (IV) or further with other color formers, the compound of this invention preferably accounts for at least 10% of the total weight of all color formers present. If its proportion is less than 10% by weight, there may be cases in which the recorded image can hardly be read with the OCR. 
     Pressure-sensitive recording materials utilizing the phthalide compound of this invention can be produced by the various known methods disclosed in inter alia Japanese Tokkyo Koho S-42-20144. A general procedure comprises microencapsulating a solution of the color former in an inner-phase solvent by a known microencapsulation technique, e.g. coacervation, interfacial polymerization, in situ polymerization, etc., using a macromolecular compound as a wall-forming material and coating the encapsulated color former on the reverse side of a support such as a sheet of wood-free paper or synthetic paper or a plastic film to provide a CB sheet. On the other hand, a developer is coated on the obverse side of another support to provide a CF sheet. When the CB sheet and CF sheet are superimposed with the coated sides in contact and a pressure is applied to the assembly, the microcapsules in the compressed area are ruptured, whereupon the color former contained in the capsules reacts with the developer to form an image on the obverse side of the CF sheet. Moreover, when a plurality of CFB sheets carrying the developer on the obverse sides and the encapsulated color former on the reverse sides of the respective supports are interposed between said CB sheet and CF sheet, a plurality of image records can be obtained. The invention can also be applied to a recording material of the self-contained type carrying both the developer and encapsulated color former on the same side of its support or to a recording material such that either the developer or the microencapsulated color former occurs within a support, with the other being present in a coating layer. 
     The developer which can be used in the pressure-sensitive recording material includes inorganic developers such as acid clay, activated clay, attapulgite, zeolite, bentonite, kaolin, etc. and organic developers such as phenolic compounds, novolac phenolic resin or its salts with polyvalent metals, aromatic carboxylic acid derivatives or their salts with polyvalent metals, salicylic acid derivatives or their salts with polyvalent metals, salicylic acid resin or its salts with polyvalent metals, terpene phenol resin or its salts with polyvalent metals, and so on. Particularly preferred are salicylic acid derivative zinc salts and p-octylphenol resin zinc salt. 
     Thermo-sensitive recording materials utilizing the phthalide compound of this invention can be manufactured by the various known methods disclosed in inter alia Japanese Tokkyo Koho S-45-14039. A general procedure comprises dispersing the color former, developer and sensitizer respectively together with an aqueous solution of a water-soluble polymer such as poly(vinyl alcohol) by means of an attriter, sandmill or the like equipment until a particle diameter not greater than several microns is attained. The sensitizer may be dispersed together with either the color former or the developer or both. The resulting respective dispersions are blended and supplemented, if necessary, with a pigment, binder, wax, metal soap, antioxidant, ultraviolet absorber, etc. to provide a thermo-sensitive coating composition. This thermo-sensitive coating composition is coated on a support such as a sheet of wood-free paper or synthetic paper or a plastic film and smoothened by calendering to provide a thermo-sensitive recording sheet. For improved color developability, the thermo-sensitive coating composition may be coated on a support having a precoated layer containing an adiabatic material such as a plastic pigment or silica. Where necessary, using an aqueous solution of a water-soluble polymer a top coat may be provided on the thermo-sensitive recording layer for imparting water resistance and chemical resistance. 
     The developer which can be used in the thermo-sensitive recording material may for example be a phenol derivative, an organic acid or its metal salt or complex, or a urea derivative. 
     Some examples of the respective types of developers are listed below. 
     The phenol derivative includes 4-tert-butylphenol, 4-octylphenol, 4-phenylphenol, 1-naphthol, 2-naphthol, hydroquinone, resorcinol, 4-tert-octylcatechol, 2,2&#39;-dihydroxybiphenyl, 4,4&#39;-dihydroxydiphenyl ether, 2,2-bis(4-hydroxyphenyl)propane [generic name: bisphenol A], tetrabromobisphenol A, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 1,4-bis(4-hydroxycumyl)benzene, 1,3,5-tris(4-hydroxycumyl)benzene, 4,4&#39;-(m-phenylenediisopropylidene)bisphenol, 4,4&#39;-(p-phenylenediisopropylidene)bisphenol, ethyl bis(4-hydroxyphenyl)acetate, n-butyl 4,4-bis(4-hydroxyphenyl)valerate, benzyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 2-phenoxyethyl 2,4-dihydroxybenzoate, dimethyl 4-hydroxyphthalate, n-propyl gallate, n-octyl gallate, n-dodecyl gallate, n-octadecyl gallate, hydroquinone monobenzyl ether, bis(3-methyl-4-hydroxyphenyl)sulfide, bis(2-methyl-4-hydroxyphenyl)sulfide, bis(3-phenyl-4-hydroxyphenyl)sulfide, bis(3-cyclohexyl-4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfone [generic name bisphenol S], tetrabromobisphenol S, bis(3-allyl-4-hydroxyphenyl)sulfone, 2,4&#39;-dihydroxydiphenyl sulfone, 4-hydroxy-4&#39;-methyldiphenyl sulfone, 4-hydroxy-4&#39;-chlorodiphenyl sulfone, 4-hydroxy-4&#39;-n-propoxydiphenyl sulfone, 4-hydroxy-4&#39;-isopropoxydiphenyl sulfone, 4-hydroxy-4&#39;-n-butoxydiphenyl sulfone, 3,4-dihydroxy-4&#39;-methyldiphenyl sulfone, 2,4-dihydroxydiphenyl sulfone, 2-methoxy-4&#39;-hydroxydiphenyl sulfone, 2-ethoxy-4&#39;-hydroxydiphenyl sulfone, bis(2-hydroxy-5-tert-butylphenyl)sulfone, bis(2-hydroxy-5-chlorophenyl)sulfone, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane and 1,5-bis(4-hydroxyphenylthio)-3-oxapentane, among others. 
     The organic carboxylic acid or its metal salt includes various organic acids such as salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-bis(α-methylbenzyl)salicylic acid, 4-(3-p-toluenesulfonylpropyloxy)salicylic acid, 5-{p-[2-(p-methoxyphenoxy)ethoxy]cumyl}salicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-methyl-5-α-methylbenzylsalicylic acid, 4-[2-(4-methoxyphenoxy)ethoxy]salicylic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-6-naphthoic acid, monobenzyl phthalate, monophenyl phthalate, 4-nitrobenzoic acid, 3-nitrobenzoic acid, 2-nitrobenzoic acid and 4-chlorobenzoic acid or their salts with various metals (e.g. nickel, zinc, aluminum, calcium, etc.) and complexes such as zinc thiocyanate antipyrine complex and molybdic acid acetylacetone complex, among others. 
     The urea derivative includes phenylthiourea, N,N&#39;-bis(3-trifluoromethylphenyl)thiourea and 1,4-bis(3-chlorophenyl)thiosemicarbazide, among others. These compounds can be used alone or in combination. 
     The sensitizer which can be used includes a variety of heat-meltable substances. The following is a partial listing of such substances. 
     The acid amide compound that can be used as said sensitizer includes caproic acid amide, capric acid amide, stearic acid amide, palmitic acid amide, oleic acid amide, stearyl urate and stearyl anilide, among others. 
     The fatty acid or its metal salt includes stearic acid, behenic acid, palmitic acid, etc. and their salts with zinc, aluminum, calcium, etc., among others. 
     The ester compound includes benzyl 4-benzyloxybenzoate, phenyl 2-naphthoate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, di(4-methylbenzyl)oxalate, di(4-chlorobenzyl)oxalate, diphenacyl glutarate, di(4-methylphenyl)carbonate and dibenzyl terephthalate, among others. 
     The hydrocarbon compound includes 4-benzylbiphenyl, m-terphenyl, fluorene, fluoranthene, 2,6-diisopropylnaphthalene and 3-benzylacenaphthene, among others. 
     The ether compound includes 2-benzyloxynaphthalene, 2-(4-methylbenzyloxy)naphthalene, 1,4-diethoxynaphthalene, 1,4-dibenzyloxynaphthalene, 1,2-diphenoxyethane, 1,2-bis(3-methylphenoxy)ethane, 1-phenoxy-2-(4-ethylphenoxy)ethane, 1-(4-methoxyphenoxy)-2-phenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, 1-(4-methoxyphenoxy)-2-(2-methylphenoxy)ethane, 4-(4-methylphenoxy)biphenyl, 1,4-bis(2-chlorobenzyloxy)benzene, 4,4&#39;-di-n-butoxydiphenyl sulfone, 1,2-diphenoxybenzene, 1,4-bis(2-chlorophenoxy)benzene, 1,4-bis(4-methylphenoxy)benzene, 1,4-bis(3-methylphenoxymethyl)benzene, 1-(4-chlorobenzyloxy)-4-ethoxybenzene, 4,4&#39;-diphenoxydiphenyl ether, 1,4-bis(4-benzylphenoxy)benzene and 1,4-bis[(4-methylphenoxy)methoxymethyl]benzene, among others. These substances can be used singly or in combination. 
     Particularly preferred are 4-benzylbiphenyl, m-terphenyl, 2-benzyloxynaphthalene, di(4-methylbenzyl)oxalate and 1,2-bis(3-methylphenoxy)ethane. 
     As the pigment, various organic and inorganic pigments can be used. Preferred species are calcium carbonate, barium sulfate, titanium dioxide, aluminum hydroxide, amorphous silica, urea-formaldehyde resin powder, polyethylene powder and so on. 
     The binder may be a water-soluble polymer or a water-insoluble polymer. Preferred examples of the water-soluble polymer are methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, starch and its derivatives, styrene-maleic anhydride copolymer hydrolyzate, ethylene-maleic anhydride copolymer hydrolyzate, isobutyrene-maleic anhydride copolymer hydrolyzate, poly(vinyl alcohol), carboxyl-modified poly(vinyl alcohol), polyacrylamide and so on. The water-insoluble polymer includes styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex and vinyl acetate emulsion, among others. 
     The wax includes, among preferred species, paraffin wax, carboxyl-modified paraffin wax and polyethylene wax. 
     The metal soap includes metal salts of higher fatty acids. Among preferred species are zinc stearate, calcium stearate and aluminum stearate. 
     The antioxidant that can be used includes hindered phenol compounds. 
     The ultraviolet absorber includes, UV absorbers in the benzophenone series and these in the benzotriazole series. 
     The following examples are intended to describe this invention in further detail and should by no means been construed as defining the scope of the invention. 
     EXAMPLES 
     Example 1 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) 
     6.9 g (0.025 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylene, 7.4 g (0.025 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 5.1 g (0.05 mol) of acetic anhydride and 10 mL of toluene were stirred together at 50°-55° C. for 4 hours. After cooling, 100 mL of toluene and 50 g of 10% sodium hydroxide (aqueous) were added. The mixture was stirred under reflux for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was stirred in 50 mL of methanol under reflex for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 8.0 g (yield 58%) of white powder. m.p. 156°-157° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 1. MS (m/z): 554 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.38 H.sub.38 N.sub.2 O.sub.2)                                
               82.26%     6.92%   5.05%                                   
Found          82.20%     6.98%   5.02%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylene used in this example was synthesized in the following manner. 
     47.7 g (0.3 mol) of 1-ethyl-2-methylindole, 60.3 g (0.45 mol) of 4&#39;-methylacetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 150 mL of toluene were stirred together at 118°-120° C. for 5 hours and after cooling, 100 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 70 g (yield 85%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 275 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.20 H.sub.21 N)                                              
              87.21%     7.70%   5.09%                                    
Found         87.12%     7.95%   5.13%                                    
______________________________________                                    
 
    
     The 2-(4-diethylaminobenzoyl)benzoic acid used was synthesized in the following manner. 
     To a mixture of 300 g of chlorobenzene and 134 g of aluminum chloride was added 149 g (1 mol) of diethylaniline dropwise under ice-cooling and stirring. Then, 74 g (0.5 mol) of phthalic anhydride was added slowly and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was collected by filtration, washed with warm water, dried and recrystallized from methanol to provide 122.5 g (yield 82.5%) of yellow-white powder. m.p. 183.5°-184° C. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 297 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.18 H.sub.19 NO.sub.3)                                       
              72.69%     6.45%   4.71%                                    
Found         72.62%     6.40%   4.72%                                    
______________________________________                                    
 
    
     Example 2 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylen-2-yl]-3-(4-dimethylaminophenyl)phthalide (compound 13) 
     9.6 g (0.037 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylene, 10.0 g (0.037 mol) of 2-(4-dimethylaminobenzoyl)benzoic acid, 7.5 g (0.074 mol) of acetic anhydride and 15 mL of toluene were stirred together at 55°-60° C. for 4.5 hours. After cooling, 100 mL of toluene and 50 g of 10% sodium hydroxide (aq.) were added. The mixture was stirred for 1 hour, after which the toluene layer was taken, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to fractionally isolate the objective compound. This product was further stirred in 50 mL of IPA under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 8.1 g (yield 42%) of white powder. m.p. 163°-165° C. Based on the following mass spectrum and elemental analysis, this powder was confirmed to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 2. MS (m/z): 512 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.35 H.sub.32 N.sub.2 O.sub.2)                                
               81.99%     6.30%   5.47%                                   
Found          81.83%     6.26%   5.46%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylene used in this example was synthesized in the following manner. 
     95.5 g (0.6 mol) of 1-ethyl-2-methylindole, 79.3 g (0.66 mol) of acetophenone, 2.0 g of p-toluenesulfonic acid monohydrate and 300 mL of toluene were stirred together at 118°-120° C. for 5 hours and after cooling, 200 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 1 hour, after which the toluene layer was taken, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 148 g (yield 94%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 261 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.19 H.sub.19 N)                                              
              87.30%     7.34%   5.36%                                    
Found         86.72%     7.75%   4.56%                                    
______________________________________                                    
 
    
     The 2-(4-diethylaminobenzoyl)benzoic acid used was synthesized in the following manner. 
     To a mixture of 300 g of chlorobenzene and 134 g of aluminum chloride was added 121 g (1 mol) of dimethylaniline dropwise under ice-cooling and stirring. Then, 74 g (0.5 mol) of phthalic anhydride was added slowly and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was collected by filtration, washed with warm water, dried and recrystallized from methanol to provide 111 g (yield 82.5%) of yellow-white powder. m.p. 198°-199° C. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 269 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.16 H.sub.15 NO.sub.3)                                       
              71.35%     5.63%   5.20%                                    
Found         71.32%     5.56%   5.19%                                    
______________________________________                                    
 
    
     Example 3 
     Production of 3-[1-(1-n-butyl-2-methylindol-3-yl)-1-(4-n-butylphenyl)ethylen-2-yl]-3-(4-di-n-butylaminophenyl)phthalide (compound 23) 
     13.8 g (0.04 mol) of 1-(1-n-butyl-2-methylindol-3-yl)-1-(4-n-butylphenyl)ethylene, 14.2 g (0.04 mol) of 2-(4-di-n-butylaminobenzoyl)benzoic acid, 8.1 g (0.08 mol) of acetic anhydride and 16 mL of toluene were stirred together at 55°-60° C. for 4.5 hours. After cooling, 100 mL of toluene and 50 g of 10% sodium hydroxide (aq.) were added. The mixture was further stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated to provide 9.6 g (yield 35%) of a colorless viscous resinous substance. This substance was verified by mass spectrometry and elemental analysis to be the title phthalide compound. MS (m/z): 680 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.47 H.sub.56 N.sub.2 O.sub.2)                                
               82.88%     8.30%   4.11%                                   
Found          82.70%     8.15%   4.03%                                   
______________________________________                                    
 
    
     The 1-(1-n-butyl-2-methylindol-3-yl)-1-(4-n-butylphenyl)ethylene used in this example was synthesized in the following manner. 
     23.8 g (0.127 mol) of 1-n-butyl-2-methylindole, 25 g (0.14 mol) of 4&#39;-n-butylacetophenone, 0.4 g of p-toluenesulfonic acid monohydrate and 60 mL of toluene were stirred together at 118°-120° C. for 5 hours and after cooling, 40 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 35 g (yield 78%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 345 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.25 H.sub.31 N)                                              
              86.89%     9.06%    4.05%                                   
Found         86.92%     9.07%    4.01%                                   
______________________________________                                    
 
    
     The 2-(4-di-n-butylaminobenzoyl)benzoic acid used was synthesized in the following manner. 
     To a mixture of 300 g of chlorobenzene and 134 g of aluminum chloride was added 205 g (1 mol) of di-n-butylaniline dropwise under ice-cooling and stirring. Then, 74 g (0.5 mol) of phthalic anhydride was added slowly and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was then poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was collected by filtration, washed with warm water, dried and recrystallized from methanol to provide 138 g (yield 78.2%) of yellow-white powder. m.p. 171°-172° C. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 353 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.22 H.sub.27 NO.sub.3)                                       
              74.74%     7.71%   3.36%                                    
Found         74.75%     7.68%   4.02%                                    
______________________________________                                    
 
    
     Example 4 
     Production of 3-[1-(1-ethyl-2-phenylindol-3-yl)-1-phenylethylen-2-yl]-3-(4-dimethylaminophenyl)phthalide (compound 41) 
     12 g (0.037 mol) of 1-(1-ethyl-2-phenylindol-3-yl)-1-phenylethylene, 10 g (0.037 mol) of 2-(4-dimethylaminobenzoyl)benzoic acid, 7.5 g (0.074 mol) of acetic anhydride and 15 mL of toluene were stirred together at 55°-60° C. for 4.5 hours. After cooling, 150 mL of toluene and 75 g of 10% sodium hydroxide (aq.) were added. The mixture was stirred under reflux for 1 hour and the toluene layer was then taken, washed with warm water, filtered and concentrated. The residue was stirred in 70 ml of IPA under reflex for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 4.6 g (yield 21.6%) of light yellow powder. m.p. 85°-88° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 3. MS (m/z): 574 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.40 H.sub.34 N.sub.2 O.sub.2)                                
               83.58%     5.97%   4.88%                                   
Found          83.60%     5.90%   4.81%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-phenylindol-3-yl)-1-phenylethylene used in this example was synthesized in the following manner. 
     66.4 g (0.3 mol) of 1-ethyl-2-phenylindole, 39.6 g (0.33 mol) of acetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 150 mL of toluene were stirred together at 118°-120° C. for 5 hours and after cooling, 100 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 10 g (yield 10%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 323 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.24 H.sub.21 N)                                              
              89.11%     6.56%   4.33%                                    
Found         89.02%     6.60%   4.28%                                    
______________________________________                                    
 
    
     Example 5 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 57) 
     18.3 g (0.07 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylene, 20.8 g (0.07 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 14.2 g (0.14 mol) of acetic anhydride and 28 mL of toluene were stirred together at 55°-60° C. for 5 hours. After cooling, 150 mL of toluene and 75 g of 10% sodium hydroxide (aq.) were added. The mixture was stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to isolate the objective compound. After concentration, this product was further stirred in 70 mL of IPA under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 4.6 g (yield 17.9%) of white powder. m.p. 123°-126° C. Based on the following mass spectrum and elemental analysis, this powder was confirmed to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 4. MS (m/z): 540 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.37 H.sub.36 N.sub.2 O.sub.2)                                
               82.18%     6.72%   5.18%                                   
Found          81.99%     6.75%   5.13%                                   
______________________________________                                    
 
    
     Example 6 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylen-2-yl]-3-(2-methyl-4-diethylaminophenyl)phthalide (compound 70) 
     9.6 g (0.037 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylene, 11.5 g (0.037 mol) of 2-(2-methyl-4-diethylaminobenzoyl)benzoic acid, 7.5 g (0.074 mol) of acetic anhydride and 15 mL of toluene were stirred together at 55°-60° C. for 4.5 hours. After cooling, 100 mL of toluene and 50 g of 10% sodium hydroxide (aq.) were added. The mixture was stirred for 1 hour, after which time the toluene layer was taken, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to isolate the objective compound. This product was further stirred in 50 mL of IPA under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 4.7 g (yield 22%) of white powder. m.p. 115°-118° C. Based on the following mass spectrum and elemental analysis, this powder was confirmed to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 5. MS (m/z): 554 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.38 H.sub.38 N.sub.2 O.sub.2)                                
               82.26%     6.92%   5.05%                                   
Found          82.29%     6.85%   5.08%                                   
______________________________________                                    
 
    
     The 2-(2-methyl-4-diethylaminobenzoyl)benzoic acid used in this example was synthesized in the following manner. 
     To a mixture of 295 g of chlorobenzene and 134 g of aluminum chloride was added 163 g (1 mol) of diethyltoluidine dropwise under ice-cooling and stirring. Then, 74 g (0.5 mol) of phthalic anhydride was added slowly and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was then poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was collected by filtration, washed with warm water, dried and recrystallized from methanol to provide 116 g (yield 74.6%) of white powder. m.p. 142°-142.5° C. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 311 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.19 H.sub.21 NO.sub.3)                                       
              73.28%     6.81%   4.50%                                    
Found         72.18%     6.84%   4.38%                                    
______________________________________                                    
 
    
     Example 7 
     Production of 3-[1-(1-n-octyl-2-phenylindol-3-yl)-1-phenylethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 84) 
     28.5 g (0.07 mol) of 1-(1-n-octyl-2-phenylindol-3-yl)-1-phenylethylene, 20.8 g (0.07 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 14.2 g (0.14 mol) of acetic anhydride and 28 mL of toluene were stirred together at 55°-60° C. for 4 hours. After cooling, 100 mL of toluene and 50 g of 10% sodium hydroxide (aq.) were added. The mixture was stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated to provide 7.2 g (yield 15%) of a colorless viscous resinous substance. This substance was verified by mass spectrometry and elemental analysis to be the title phthalide compound. MS (m/z): 686 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.48 H.sub.50 N.sub.2 O.sub.2)                                
               83.91%     7.35%   4.08%                                   
Found          83.96%     7.30%   4.05%                                   
______________________________________                                    
 
    
     The 1-(1-n-octyl-2-phenylindol-3-yl)-1-phenylethylene used in this example was synthesized in the following manner. 
     61.0 g (0.2 mol) of 1-n-octyl-2-phenylindole, 26.4 g (0.22 mol) of acetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 100 mL of toluene were stirred together at 118°-120° C. for 5 hours and after cooling, 100 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 71 g (yield 87%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 407 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.30 H.sub.33 N)                                              
              88.39%     8.18%   3.44%                                    
Found         88.29%     8.20%   3.47%                                    
______________________________________                                    
 
    
     Example 8 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(2-ethoxy-4-di-n-butylaminophenyl)phthalide (compound 87) 
     41.3 g (0.15 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylene, 59.6 g (0.15 mol) of 2-(2-ethoxy-4-di-n-butylaminobenzoyl)benzoic acid, 40.8 g (0.40 mol) of acetic anhydride and 10 mL of toluene were stirred together at 45°-50° C. for 4 hours. After cooling, 150 mL of toluene and 150 mL of warm water were added. The mixture was stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated to provide 19.5 g (yield 19.9%) of pale brown oil. This oil was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 6. MS (m/z): 654 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.44 H.sub.50 N.sub.2 O.sub.3)                                
               80.70%     7.70%   4.28%                                   
Found          80.70%     7.81%   4.33%                                   
______________________________________                                    
 
    
     The 2-(2-ethoxy-4-di-n-butylaminobenzoyl)benzoic acid used in this example was synthesized in the following manner. 
     To a mixture of 325 g of chlorobenzene and 149.9 g of aluminum chloride was added 274.3 g (1.1 mol) of 3-n-ethoxy-N,N-di-n-butylaniline dropwise under ice-cooling and stirring. Then, 81.5 g (0.55 mol) of phthalic anhydride was added and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was then poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was taken, diluted with 200 mL of toluene and extracted with aqueous sodium hydroxide solution. The extract was precipitated from diluted hydrochloric acid and the precipitate was recovered, washed with warm water and dried. It was then recrystallized from toluene-methanol to provide 111.8 g (yield 51.1%) of yellowish white powder. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 397 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.24 H.sub.31 NO.sub.4)                                       
              72.52%     7.86%   3.52%                                    
Found         72.46%     7.81%   3.49%                                    
______________________________________                                    
 
    
     Example 9 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(2-n-butoxy-4-diethylaminophenyl)phthalide (compound 89) 
     41.3 g (0.15 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylene, 55.4 g (0.15 mol) of 2-(2-n-butoxy-4-dimethylaminobenzoyl)benzoic acid, 40.8 g (0.40 mol) of acetic anhydride and 15 mL of toluene were stirred together at 55°-60° C. for 4.5 hours. After cooling, 150 mL of toluene and 150 mL of warm water were added. The mixture was stirred for 1 hour, after which time the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated to provide 16.1 g (yield 17.1%) of yellow oil. This oil was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 7. MS (m/z): 626 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.42 H.sub.46 N.sub.2 O.sub.3)                                
               80.48%     7.40%   4.47%                                   
               80.55%     7.38%   4.48%                                   
______________________________________                                    
 
    
     The 2-(2-n-butoxy-4-diethylaminobenzoyl)benzoic acid used in this example was synthesized in the following manner. 
     To a mixture of 325 g of chlorobenzene and 149.9 g of aluminum chloride was added 243.1 g (1.1 mol) of 3-n-ethoxy-N,N-di-n-butylaniline dropwise under ice-cooling and stirring. Then, 81.4 g (0.55 mol) of phthalic anhydride was added and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was then poured into 1 L of water and the chlorobenzene was distilled off. The oil layer was separated, diluted with 200 mL of toluene and extracted with aqueous sodium hydroxide solution. The extract was treated with diluted hydrochloric acid and the resulting precipitate was collected and washed with warm water. It was then recrystallized from toluene-methanol to provide 100.6 g (yield 49.5%) of yellowish white powder. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 369 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.22 H.sub.27 NO.sub.4)                                       
              71.52%     7.37%   3.79%                                    
Found         71.59%     7.31%   3.83%                                    
______________________________________                                    
 
    
     Example 10 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylen-2-yl]-3-[4-N-ethyl-N-(4-ethoxyphenyl)aminophenyl]phthalide (compound 91) 
     20.9 g (0.08 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-phenylethylene, 31.1 g (0.08 mol) of 2-[4-N-ethyl-N-(4-ethoxyphenyl)aminobenzoyl)benzoic acid, 16.3 g (0.16 mol) of acetic anhydride and 33 mL of toluene were stirred together at 60°-65° C. for 4 hours. After cooling, 300 mL of toluene and 180 g of 2% sodium hydroxide (aq.) were added. The mixture was further stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated. The residue was stirred in 500 mL of n-hexane under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 9.1 g (yield 18%) of white powder. m.p. 112°-113° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 8. MS (m/z): 632 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.43 H.sub.40 N.sub.2 O.sub.3)                                
               81.62%     6.37%   4.43%                                   
Found          81.73%     6.32%   4.49%                                   
______________________________________                                    
 
    
     The 2-[4-N-ethyl-N-(4-ethoxyphenyl)aminobenzoyl)benzoic acid used in this example was synthesized in the following manner. 
     To a mixture of 319 g of chlorobenzene and 160.0 g of aluminum chloride was added 136.2 g (0.56 mol) of N-ethyl-N-(4-ethoxyphenyl)aniline dropwise under ice-cooling and stirring. Then, 88.8 g (0.60 mol) of phthalic anhydride was added and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was then poured into 1 L of water and the chlorobenzene was distilled off. The oil layer was separated, diluted with 100 mL of toluene and extracted with aqueous sodium hydroxide solution. The extract was treated with diluted hydrochloric acid and the resulting precipitate was collected by filtration, washed with warm water and dried. It was then recrystallized from methanol to provide 74.6 g (yield 34.2%) of green-white powder. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 389 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.24 H.sub.23 NO.sub.4)                                       
              74.02%     5.95%   3.60%                                    
Found         73.98%     5.91%   3.54%                                    
______________________________________                                    
 
    
     Example 11 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(2-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 92) 
     110.2 g (0.40 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(2-methylphenyl)ethylene, 118.9 g (0.40 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 81.7 g (0.80 mol) of acetic anhydride and 160 mL of toluene were stirred together at 50°-55° C. for 5 hours. After cooling, 700 mL of toluene and 200 g of 5% sodium hydroxide (aq.) were added. The mixture was stirred under reflux for 2 hours and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was stirred in 1500 ml of methanol under reflex for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide a yellow-white powder. The powder was recrystallized from a solvent mixture of 1500 mL of methanol and 750 mL of toluene to give 87.2 g (yield 39.3%) of white powder. m.p. 188°-190° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 9. MS (m/z): 554 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.38 H.sub.38 N.sub.2 O.sub.2)                                
               82.28%     6.90%   5.05%                                   
Found          82.33%     6.89%   5.09%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-(2-methylphenyl)ethylene used in this example was synthesized in the following manner. 
     79.6 g (0.50 mol) of 1-ethyl-2-methylindole, 80.5 g (0.60 mol) of 2&#39;-methylacetophenone, 1.5 g of p-toluenesulfonic acid monohydrate and 200 mL of toluene were stirred together at 118°-120° C. for 4 hours and after cooling, 600 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 10 minutes, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 117.0 g (yield 85%) of light-red liquid. Based on the following analyses, this liquid was confirmed to be the objective ethylene compound. MS (m/z): 275 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.20 H.sub.21 N)                                              
              87.23%     7.69%   5.09%                                    
Found         87.30%     7.75%   5.01%                                    
______________________________________                                    
 
    
     Example 12 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(3-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 97) 
     82.6 g (0.30 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(3-methylphenyl)ethylene, 89.2 g (0.30 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 61.3 g (0.60 mol) of acetic anhydride and 120 mL of toluene were stirred together at 50°-55° C. for 4.0 hours. After cooling, 1000 mL of toluene and 500 g of 5% sodium hydroxide (aq.) were added. The mixture was stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to isolate the objective compound. This product was purified by recrystallization from a mixture of 200 mL of methanol and 40 mL of toluene to give a white granular precipitate. The melting point of this granular product was 105°-112° C. (a foam produced). The granules were stirred in 800 mL of n-hexane under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 36.1 g (yield 21.7%) of white powder. m.p. 104°-105° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 10. MS (m/z): 554 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.38 H.sub.38 N.sub.2 O.sub.2)                                
               82.28%     6.90%   5.05%                                   
Found          82.20%     6.85%   5.11%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-(3-methylphenyl)ethylene used in this example was synthesized in the following manner. 
     47.7 g (0.30 mol) of 1-ethyl-2-methylindole, 41.5 g (0.31 mol) of 3&#39;-methylacetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 150 mL of toluene were stirred together at 118°-120° C. for 4 hours and after cooling, 300 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 1 hour, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 58.7 g (yield 71%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 275 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.20 H.sub.21 N)                                              
              87.23%     7.69%   5.09%                                    
Found         87.31%     7.78%   4.99%                                    
______________________________________                                    
 
    
     Example 13 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methoxyphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 98) 
     87.4 g (0.30 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methoxyphenyl)ethylene, 89.2 g (0.30 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 61.3 g (0.60 mol) of acetic anhydride and 120 mL of toluene were stirred together at 50°-55° C. for 2.0 hours. After cooling, 800 mL of toluene and 600 g of 1% sodium hydroxide (aq.) were added. The mixture was further stirred for 1.5 hours and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated. The concentrate was stirred in a solvent mixture of 1200 mL of methanol and 120 mL of toluene under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide white granules. m.p. 109°-115° C. (a foam produced). The granules were then stirred in 1000 ml of n-hexane under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 58.2 g (yield 34.0%) of white granules. m.p. 179°-181° C. This granular product was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 11. MS (m/z): 570 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.38 H.sub.38 N.sub.2 O.sub.3)                                
               79.97%     6.71%   4.91%                                   
Found          80.06%     6.81%   4.99%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methoxyphenyl)ethylene used in this example was synthesized in the following manner. 
     79.6 g (0.50 mol) of 1-ethyl-2-methylindole, 82.6 g (0.55 mol) of 4&#39;-methoxyacetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 150 mL of toluene were stirred together at 118°-120° C. for 4 hours and after cooling, 100 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 10 minutes, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 128.2 g (yield 88%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 291 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.20 H.sub.21 NO)                                             
              82.44%     7.26%   4.81%                                    
Found         82.50%     7.24%   4.85%                                    
______________________________________                                    
 
    
     Example 14 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-chlorophenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 108) 
     88.7 g (0.30 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-chlorophenyl)ethylene, 89.2 g (0.30 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 61.3 g (0.60 mol) of acetic anhydride and 120 mL of toluene were stirred together at 50°-55° C. for 4.0 hours. After cooling, 1000 mL of toluene and 500 g of 5% sodium hydroxide (aq.) were added. The mixture was further stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent and the eluate was concentrated. The concentrate was stirred in 1000 mL of methanol under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 52.6 g (yield 30.5%) of white powder. m.p. 144°-146° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 12. MS (m/z): 574 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
                C         H       N                                       
______________________________________                                    
Calcd. (C.sub.37 H.sub.35 N.sub.2 O.sub.2 Cl)                             
                77.27%    6.13%   4.87%                                   
Found           77.31%    6.08%   4.81%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-(4-chlorophenyl)ethylene used in this example was synthesized in the following manner. 
     79.6 g (0.50 mol) of 1-ethyl-2-methylindole, 80.4 g (0.52 mol) of 4&#39;-chloroacetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 150 mL of toluene were stirred together at 118°-120° C. for 4 hours and after cooling, 100 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 10 minutes, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using hexane as an eluent to provide 121.3 g (yield 82%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 295 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.19 H.sub.18 NCl)                                            
              77.15%     6.13%   4.74%                                    
Found         77.20%     6.19%   4.70%                                    
______________________________________                                    
 
    
     Example 15 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)benzo(f)phthalide (compound 144) 
     41.3 g (0.15 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylene, 52.1 g (0.15 mol) of 2-carboxy-3-(4-diethylaminobenzoyl)naphthalene, 40.8 g (0.40 mol) of acetic anhydride and 10 mL of toluene were stirred together at 45°-50° C. for 4.0 hours. After cooling, 150 mL of toluene and 150 mL of water were added. The mixture was further stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to obtain the objective fraction. This fraction was further purified by recrystallization from methanol to provide 19.5 g (yield 21.5%) of white powder. m.p. 182°-184° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 13. MS (m/z): 604 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.42 H.sub.40 N.sub.2 O.sub.2)                                
               83.41%     6.67%   4.63%                                   
Found          83.29%     6.70%   4.60%                                   
______________________________________                                    
 
    
     The 2-carboxy-3-(4-diethylaminobenzoyl)naphthalene used in this example was synthesized in the following manner. 
     To a mixture of 207 g of chlorobenzene and 93.5 g of aluminum chloride was added 104.3 g (0.70 mol) of diethylaniline dropwise under ice-cooling and stirring. Then, 69.3 g (0.35 mol) of 2,3-naphthalenedicarboxylic anhydride was added and the mixture was stirred at 45°-50° C. for 4 hours. The reaction mixture was poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was separated, diluted with 100 mL of toluene and extracted with 500 g of 15% aqueous sodium hydroxide solution. The extract was precipitated from 5% hydrochloric acid and the precipitate was collected and washed with warm water. It was then recrystallized from toluene-methanol to provide 85.0 g (yield 69.9%) of yellow-greenish white powder. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 347 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.22 H.sub.21 NO.sub.3)                                       
              76.06%     6.09%   4.03%                                    
Found         76.00%     6.06%   4.10%                                    
______________________________________                                    
 
    
     Example 16 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)-4,5,6,7-tetrachlorophthalide (compound 155) 
     41.3 g (0.15 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylene, 65.3 g (0.15 mol) of 2-(4-diethylaminobenzoyl)-3,4,5,6-tetrachlorobenzoic acid, 40.8 g (0.40 mol) of acetic anhydride and 10 mL of toluene were stirred together at 45°-50° C. for 4.0 hours. After cooling, 150 mL of toluene and 150 mL of water were added. The mixture was further stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to obtain the objective fraction. This fraction was further purified by recrystallization from methanol to provide 31.4 g (yield 30.2%) of light yellow white powder. m.p. 175°-177° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. Its infrared absorption spectrum is presented in FIG. 14. MS (m/z): 692 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
                C         H       N                                       
______________________________________                                    
Calcd. (C.sub.38 H.sub.34 N.sub.2 O.sub.2 Cl.sub.4)                       
                65.91%    4.95%   4.05%                                   
Found           65.95%    4.98%   4.10%                                   
______________________________________                                    
 
    
     The 2-(4-diethylaminobenzoyl)-3,4,5,6-tetrachlorobenzoic acid used in this example was synthesized in the following manner. 
     To a mixture of 944 g of chlorobenzene and 227 g of aluminum chloride was added 253.3 g (1.70 mol) of diethylaniline dropwise under ice-cooling and stirring. Then, 243.1 g (0.85 mol) of 3,4,5,6-tetrachlorophthalic anhydride was added and the mixture was stirred at 35°-40° C. for 2 hours. The reaction mixture was then poured into 1 L of water and the chlorobenzene was distilled off. The precipitate was collected, washed with warm water, dried and recrystallized from toluene-methaol to provide 330.2 g (yield 89%) of yellowish white powder. This powder was verified by the following analyses to be the objective benzoic acid derivative. MS (m/z): 435 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
                C         H       N                                       
______________________________________                                    
Calcd. (C.sub.18 H.sub.15 NO.sub.3 Cl.sub.4)                              
                49.69%    3.47%   3.22%                                   
Found           49.77%    3.53%   3.29%                                   
______________________________________                                    
 
    
     Comparison Example of Synthesis-1 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-dimethylaminophenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound A) 
     10.65 g (0.035 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-dimethylaminophenyl)ethylene, 10.41 g (0.035 mol) of 2-(4-diethylaminobenzoyl)benzoic acid, 7.1 g (0.07 mol) of acetic anhydride and 15 mL of toluene were stirred together at 55°-60° C. for 4.5 hours. After cooling, 100 mL of toluene and 50 g of 10% sodium hydroxide (aq.) were added. The mixture was stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to isolate the objective compound. This product was further stirred in 50 mL of hexane under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 9.3 g (yield 45.5%) of beige powder. m.p. 76°-78° C. This powder was further purified by recrystallization from 150 mL of IPA to provide 7.6 g (yield 37.2%) of white powder. m.p. 149°-152° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. MS (m/z): 583 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.39 H.sub.41 N.sub.3 O.sub.2)                                
               80.23%     7.09%   7.12%                                   
Found          80.25%     7.05%   7.13%                                   
______________________________________                                    
 
    
     The 1-(1-ethyl-2-methylindol-3-yl)-1-(4-dimethylaminophenyl)ethylene used in this comparison example of synthesis was synthesized in the following manner. 
     22.1 g (0.139 mol) of 1-ethyl-2-methylindole, 25.0 g (0.153 mol) of 4&#39;-dimethylaminoacetophenone, 1.0 g of p-toluenesulfonic acid monohydrate and 75 mL of toluene were stirred together at 118°-122° C. for 6.5 hours and after cooling, 100 mL of toluene and 50 g of 1% sodium hydroxide (aq.) was added. The mixture was further stirred for 10 minutes, after which the toluene layer was separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene as an eluent to provide 18.3 g (yield 43.2%) of light-red liquid. This liquid was verified by the following analyses to be the objective ethylene compound. MS (m/z): 304 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
              C          H       N                                        
______________________________________                                    
Calcd. (C.sub.21 H.sub.24 N.sub.2)                                        
              82.85%     7.95%   9.20%                                    
Found         82.80%     7.91%   9.16%                                    
______________________________________                                    
 
    
     Comparison Example of Synthesis-2 
     Production of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-dimethylaminophenyl)ethylen-2-yl]-3-(2-n-butoxy-4-diethylaminophenyl)phthalide (compound B) 
     23.7 g (0.078 mol) of 1-(1-ethyl-2-methylindol-3-yl)-1-(4-dimethylaminophenyl)ethylene, 45.0 g (0.122 mol) of 2-(2-n-butoxy-4-diethylaminobenzoyl)benzoic acid, 24.9 g (0.244 mol) of acetic anhydride and 40 mL of toluene were stirred together at 50°-53° C. for 1.5 hours. After cooling, 100 g of 10% sodium hydroxide (aq.) and 100 mL of toluene were added. The mixture was further stirred for 1 hour and the toluene layer was then separated, washed with warm water, filtered and concentrated. The residue was subjected to column chromatography on silica gel using toluene-ethyl acetate as an eluent and the eluate was concentrated. The residue was stirred in 50 mL of methanol under reflux for 1 hour. After cooling, the precipitate was collected by filtration and dried to provide 15.6 g (yield 30.5%) of greenish white powder. m.p. 148°-151° C. This powder was verified by mass spectrometry and elemental analysis to be the title phthalide compound. MS (m/z): 655 (M + ) 
     
         ______________________________________                                    
Elemental analysis:                                                       
               C          H       N                                       
______________________________________                                    
Calcd. (C.sub.43 H.sub.49 N.sub.3 O.sub.3)                                
               78.74%     7.53%   6.41%                                   
Found          78.70%     7.48%   6.43%                                   
______________________________________                                    
 
    
     Example 17 
     Production of a near infrared absorber 
     0.15 g of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and 0.30 g of benzyl p-hydroxybenzoate were heated together to provide a melt. 
     The melt was coated thinly on a glass sheet and cooled. The absorption characteristics of the near infrared absorbing device thus fabricated were determined on Spectrophotometer UV365 (Shimadzu Corporation). This device was found to have an absorption maximum at 720 nm. The region corresponding to not less than 80% absorbance relative to this absorption maximum was 700 nm-750 nm and the region corresponding to not less than 50% absorbance relative to said absorption maximum was 670 nm-770nm. 
     The absorption spectrum of a glass sheet coated with the near infrared absorber of this invention [the reaction product of Compound 1 and benzyl p-hydroxybenzoate] is presented in FIG. 15. 
     Comparison Example 1 
     Production of a near infrared absorber 
     The procedure of Example 17 was repeated except that compound A as synthesized in Comparison Example of Synthesis-1 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4diethylaminophenyl)phthalide (compound 1). The resulting near infrared absorber was green-blue with a absorption maximum at 745 nm and a characteristic absorption at 620 nm. The region corresponding to not less than 80% absorbance relative to the above absorption maximum was 690 nm-780 nm and the region corresponding to not less than 50% absorbance relative to said absorption maximum was 585 nm-800 nm. 
     The absorption spectrum of a glass sheet coated with the reaction product of compound A (Comparison Example of Synthesis-1) and benzyl p-hydroxybenzoate is presented in FIG. 16. 
     Example 18 
     Production of a near infrared absorber 
     In 5 ml of THF were dissolved 15 mg of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and 30 mg of bisphenol A to prepare a solution. 
     This solution was coated on a sheet of wood-free paper and allowed to dry. The paper carrying the near infrared absorber was as white as the substrate paper. 
     The absorption characteristics of the above paper were determined in terms of reflectance using Spectrophotometer UV365 (Shimadzu Corporation). The absorbance is expressed by the following equation. 
     
         Absorbance (%)=100-reflectance (%) 
    
     (The term `absorbance` as used herein means the value calculated by means of the above equation). 
     The above paper was found to have an absorption maximum at 725 nm and the wavelength region corresponding to not less than 80% absorbance relative to the above absorption maximum was 675 nm-770 nm. 
     The reflectance spectrum of the paper coated with the near infrared absorber of this invention (the product of reaction between compound 1 and bisphenol A) is presented in FIG. 17. 
     Comparison Example 2 
     Production of a near infrared absorber 
     The procedure of Example 18 was repeated except that compound A as synthesized in Comparison Example of Synthesis-1 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1). The coated paper was distinct green-blue. This paper had an absorption maximum at 735 nm and the wavelength region corresponding to not less than 80% absorbance relative to said absorption maximum was 560 nm-815 nm. 
     The reflectance spectrum of the paper coated with the product of reaction between compound A (Comparison Example of Synthesis-1) and bisphenol A is presented in FIG. 18. 
     Examples 19-14 
     Production of near infrared absorbers 
     The procedure of Example 18 was repeated except that the electron-accepting compounds listed below in Table 2 were respectively used in lieu of bisphenol A. The results are shown in Table 2. The sheets of paper coated with the respective near infrared absorbers produced above absorbed strongly the near infrared region as did the coated paper fabricated in Example 18 but absorbed little the visible region so that the papers were either white or of pale color. 
     Comparison Examples 3-9 
     Production of near infrared absorbers 
     The procedure of Example 18 was repeated except that compound A was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and that the electron accepting compounds shown below in Table 2 were respectively used. The results are shown in Table 2. 
     
                       TABLE 2                                                     
______________________________________                                    
             Absorption                                                   
             Characteristics                                              
               Maxi-   The region                                         
               mum     of ≧80% ab-                                 
               absorp- sorbance rel-                                      
       Electron-                                                          
               tion    ative to max-                                      
       accepting                                                          
               wave-   imum absorp-                                       
                                  Color, by                               
       com-    length  tion       visual                                  
       pound   (nm)    (nm)       obervation                              
______________________________________                                    
Example 19                                                                
         D-8       715     685-750  White                                 
Example 20                                                                
         AP-5      720     690-760  White                                 
Example 21                                                                
         TG-SA     725     650-740  Pale                                  
                                    grayish white                         
Example 22                                                                
         PHB       725     690-755  White                                 
Example 23                                                                
         Tamanol P 720     695-745  White                                 
Example 24                                                                
         Hitanol   720     685-755  White                                 
         1501                                                             
Comparison                                                                
         D-8       740     565-805  Green-blue                            
Example 3                                                                 
Comparison                                                                
         AP-5      740     570-805  Green-blue                            
Example 4                                                                 
Comparison                                                                
         TG-SA     745     565-815  Green-blue                            
Example 5                                                                 
Comparison                                                                
         PHB       740     570-805  Light green-                          
Example 6                           blue                                  
Comparison                                                                
         Bisphenol S                                                      
                   745     555-815  Green-blue                            
Example 7                                                                 
Comparison                                                                
         Tamanol P 740     595-780  Green-blue                            
Example 8                                                                 
Comparison                                                                
         Hariester 740     620-775  Light Blue                            
Example 9                                                                 
         510                                                              
______________________________________                                    
 In the table, D8 stands for 4hydroxy-4isopropoxy-diphenyl sulfone, AP5 fo
 2,2bis(p-hydroxyphenyl)-4-methyl-pentane, TGSA for                       
 3,3diallyl-4,4dihydroxydiphenyl sulfone, and PHB for benzyl              
 phydroxybenzoate.                                                        
 
    
     Examples 25-87 
     Production of near infrared absorbers 
     The procedure of Example 18 was repeated except that the phthalide compounds listed in Table 3 were respectively used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and that the electron accepting compounds shown in Table 3 were respectively used. The results are shown in Table 3. 
     The reflectance spectra of the coated papers according to Examples 28, 34, 45, 51, 61, 66, 67, 71, 75, 76, 79, 83 and 86 are presented in FIG. 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 and 31, respectively. 
     Comparison Examples 10-12 
     The procedure of Example 18 was repeated except that compound B prepared in Comparison Example of Synthesis-2 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and that the electron accepting compounds shown below in Table 3 were respectively used. The results are shown in Table 3. 
     
                                           TABLE 3                                 
__________________________________________________________________________
                      Absorption characteristics                          
                            The region                                    
                            of ≧80% ab-                            
                            sorbance rel-                                 
                      Maximum                                             
                            ative to max-                                 
               Electron-                                                  
                      absorption                                          
                            imum absorp-                                  
                                   Color, by                              
       Phthalide                                                          
               accepting                                                  
                      wavelength                                          
                            tion   visual                                 
       Compound No.                                                       
               compound                                                   
                      (nm)  (nm)   observation                            
__________________________________________________________________________
Example 25                                                                
       Compound 13                                                        
               Bisphenol A                                                
                      725   690-760                                       
                                   White                                  
Example 26                                                                
       Compound 13                                                        
               D-8    720   695-745                                       
                                   White                                  
Example 27                                                                
       Compound 13                                                        
               AP-5   725   695-750                                       
                                   White                                  
Example 28                                                                
       Compound 13                                                        
               TG-SA  720   660-770                                       
                                   Pale greenish                          
                                   white                                  
Example 29                                                                
       Compound 13                                                        
               PHB    720   700-745                                       
                                   White                                  
Example 30                                                                
       Compound 13                                                        
               Bisphenol S                                                
                      725   650-780                                       
                                   Pale greenish                          
                                   white                                  
Example 31                                                                
       Compound 13                                                        
               Tamanol P                                                  
                      720   695-735                                       
                                   White                                  
Example 32                                                                
       Compound 13                                                        
               Hitanol 1501                                               
                      720   700-740                                       
                                   White                                  
Example 33                                                                
       Compound 23                                                        
               Bisphenol A                                                
                      730   685-775                                       
                                   Pale greenish                          
                                   white                                  
Example 34                                                                
       Compound 23                                                        
               D-8    720   685-755                                       
                                   White                                  
Example 35                                                                
       Compound 23                                                        
               AP-5   725   685-765                                       
                                   White                                  
Example 36                                                                
       Compound 23                                                        
               TG-SA  725   650-750                                       
                                   Pale green                             
Example 37                                                                
       Compound 23                                                        
               PHB    720   680-765                                       
                                   White                                  
Example 38                                                                
       Compound 23                                                        
               Tamanol P                                                  
                      720   700-740                                       
                                   White                                  
Example 39                                                                
       Compound 23                                                        
               Hitanol 1501                                               
                      720   695-735                                       
                                   White                                  
Example 40                                                                
       Compound 41                                                        
               Bisphenol A                                                
                      725   700-755                                       
                                   White                                  
Example 41                                                                
       Compound 41                                                        
               D-8    725   705-750                                       
                                   White                                  
Example 42                                                                
       Compound 41                                                        
               AP-5   725   705-750                                       
                                   White                                  
Example 43                                                                
       Compound 41                                                        
               TG-SA  725   685-755                                       
                                   Pale greenish                          
                                   white                                  
Example 44                                                                
       Compound 41                                                        
               PHB    725   680-770                                       
                                   White                                  
Example 45                                                                
       Compound 41                                                        
               Bisphenol S                                                
                      730   675-775                                       
                                   Pale grayish                           
                                   white                                  
Example 46                                                                
       Compound 41                                                        
               Tamanol P                                                  
                      720   690-750                                       
                                   White                                  
Example 47                                                                
       Compound 57                                                        
               Bisphenol A                                                
                      720   655-765                                       
                                   Pale greenish                          
                                   white                                  
Example 48                                                                
       Compound 57                                                        
               D-8    720   690-750                                       
                                   White                                  
Example 49                                                                
       Compound 57                                                        
               AP-5   720   690-755                                       
                                   White                                  
Example 50                                                                
       Compound 57                                                        
               TG-SA  720   660-770                                       
                                   Pale green                             
Example 51                                                                
       Compound 57                                                        
               PHB    720   690-760                                       
                                   White                                  
Example 52                                                                
       Compound 57                                                        
               Tamanol P                                                  
                      720   695-740                                       
                                   White                                  
Example 53                                                                
       Compound 57                                                        
               Hitanol 1501                                               
                      720   695-740                                       
                                   White                                  
Example 54                                                                
       Compound 70                                                        
               Bisphenol A                                                
                      730   695-775                                       
                                   White                                  
Example 55                                                                
       Compound 70                                                        
               D-8    720   695-760                                       
                                   White                                  
Example 56                                                                
       Compound 70                                                        
               AP-5   725   695-765                                       
                                   White                                  
Example 57                                                                
       Compound 70                                                        
               TG-SA  725   680-790                                       
                                   Pale yel-                              
                                   lowish white                           
Example 58                                                                
       Compound 70                                                        
               PHB    720   695-755                                       
                                   White                                  
Example 59                                                                
       Compound 70                                                        
               Bisphenol S                                                
                      725   675-810                                       
                                   Pale yel-                              
                                   lowish white                           
Example 60                                                                
       Compound 70                                                        
               Hitanol 1501                                               
                      725   695-760                                       
                                   White                                  
Example 61                                                                
       Compound 87                                                        
               Bisphenol A                                                
                      695   640-750                                       
                                   Pale grayish                           
                                   white                                  
Example 62                                                                
       Compound 87                                                        
               D-8    695   650-735                                       
                                   Pale grayish                           
                                   white                                  
Example 63                                                                
       Compound 87                                                        
               PHB    690   630-740                                       
                                   White                                  
Example 64                                                                
       Compound 89                                                        
               Bisphenol A                                                
                      690   610-745                                       
                                   Pale grayish                           
                                   white                                  
Example 65                                                                
       Compound 89                                                        
               D-8    685   615-730                                       
                                   Pale grayish                           
                                   white                                  
Example 66                                                                
       Compound 89                                                        
               PHB    695   655-740                                       
                                   White                                  
Example 67                                                                
       Compound 91                                                        
               Bisphenol A                                                
                      725   700-760                                       
                                   White                                  
Example 68                                                                
       Compound 91                                                        
               D-8    720   690-755                                       
                                   White                                  
Example 69                                                                
       Compound 91                                                        
               PHB    725   700-755                                       
                                   White                                  
Example 70                                                                
       Compound 92                                                        
               Bisphenol A                                                
                      720   665-760                                       
                                   Pale greenish                          
                                   white                                  
Example 71                                                                
       Compound 92                                                        
               D-8    715   675-750                                       
                                   Pale greenish                          
                                   white                                  
Example 72                                                                
       Compound 92                                                        
               PHB    715   685-745                                       
                                   White                                  
Example 73                                                                
       Compound 97                                                        
               Bisphenol A                                                
                      720   680-760                                       
                                   Pale greenish                          
                                   white                                  
Example 74                                                                
       Compound 97                                                        
               D-8    720   690-750                                       
                                   White                                  
Example 75                                                                
       Compound 97                                                        
               PHB    720   690-750                                       
                                   White                                  
Example 76                                                                
       Compound 98                                                        
               Bisphenol A                                                
                      720   675-765                                       
                                   Pale grayish                           
                                   white                                  
Example 77                                                                
       Compound 98                                                        
               D-8    715   680-755                                       
                                   White                                  
Example 78                                                                
       Compound 98                                                        
               PHB    715   680-760                                       
                                   White                                  
Example 79                                                                
       Compound 108                                                       
               Bisphenol A                                                
                      730   695-765                                       
                                   White                                  
Example 80                                                                
       Compound 108                                                       
               D-8    725   700-750                                       
                                   White                                  
Example 81                                                                
       Compound 108                                                       
               PHB    725   700-755                                       
                                   White                                  
Example 82                                                                
       Compound 144                                                       
               Bisphenol A                                                
                      720   650-785                                       
                                   Pale grayish                           
                                   white                                  
Example 83                                                                
       Compound 144                                                       
               D-8    715   665-770                                       
                                   Pale grayish                           
                                   white                                  
Example 84                                                                
       Compound 144                                                       
               PHB    715   670-770                                       
                                   White                                  
Example 85                                                                
       Compound 155                                                       
               Bisphenol A                                                
                      740   700-780                                       
                                   Pale green-                            
                                   white                                  
Example 86                                                                
       Compound 155                                                       
               D-8    740   685-780                                       
                                   Pale greenish                          
                                   white                                  
Example 87                                                                
       Compound 155                                                       
               PHB    740   705-765                                       
                                   White                                  
Comparison                                                                
       Compound B                                                         
               Bisphenol A                                                
                      730   590-780                                       
                                   Green-blue                             
Example 10                                                                
Comparison                                                                
       Compound B                                                         
               D-8    730   570-785                                       
                                   Green-blue                             
Example 11                                                                
Comparison                                                                
       Compound B                                                         
               PHB    730   560-790                                       
                                   Green-blue                             
Example 12                                                                
__________________________________________________________________________
 In the table, Tamanol P: palkylphenol-formaldehyde resin, Arakawa Chemica
 Industries, Ltd.; Hitanol 1501: palkylphenol-formaldehyde resin, Hitachi 
 Chemical Co., Ltd.                                                       
 
    
     Comparison Example 13 
     The procedure of Example 18 was repeated except that compound B as synthesized in Comparison Example of Synthesis-2 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl ]-3-(4-diethylaminophenyl)phthalide (compound 1) and the quantity of THF was doubled (10 mL). The paper carrying the near infrared absorber thus produced was green-blue with an absorption maximum at 730 nm and a characteristic absorption at 610 nm. The wavelength region corresponding to not less than 80% absorbance relative to the above absorption maximum was 675 nm-770 nm and the region corresponding to not less than 50% absorbance relative to said absorption maximum was 565 nm-790 nm. The reflection spectrum of this paper (a sheet of paper coated with the product of reaction between compound B and bisphenol A) is presented in FIG. 32. 
     Example 88 
     Production of a secret ink 
     A secret ink was produced by dissolving 10 mg of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and 20 mg of bisphenol A in an acrylic varnish (methyl acrylate-methyl methacrylate). 
     Using this ink and a pen, characters were written on a sheet of paper and dried. The resulting record could not be read with the eye but could be read with the OCR. 
     Examples 89-103 
     Production of a secret ink 
     The procedure of Example 88 was repeated except that the phthalide compounds synthesized in Examples 2-16 were respectively used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide to prepare secret inks and using each ink and a pen, characters were written on sheets of paper. The resulting image records were as satisfactory as the record obtained in Example 88. 
     Example 104 
     Production of a pressure-sensitive recording material 
     In 47 g of KMC-113 (a solvent manufactured by Kureha Chemical Industry Co., Ltd.) was dissolved 3 g of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) with heating. Separately, 5 g of a system modifier (SM-100, manufactured by Mitsui Toatsu Chemicals, Inc.) was added to 100 g of water and the mixture was adjusted to pH 4 with aqueous sodium hydroxide solution. To this solution was added the solution prepared above together with 10 g of melamineformaldehyde precondensate (UMC-300, manufactured by Mitsui Toatsu Chemicals, Inc.) and the mixture was emulsified with a homo-mixer until the size of oil droplets reached 4 microns. The emulsion was heated to 60° C. with stirring and further stirred at this temperature for 1 hour. After cooling to ambient temperature, the emulsion was adjusted to pH 7.5 with 25% aqueous ammonia to provide a microencapsulated color former dispersion. 
     Ten (10) grams of the microcapsule dispersion thus obtained was mixed thoroughly with 2 g of wheat starch and 1 g of latex and the composition was coated in a coverage of 5 g (solids)/m 2  on a sheet of wood-free paper weighing 50 g/m 2  to provide a CB sheet. 
     The CB sheet thus prepared was superimposed on a CF sheet having a zinc-modified p-octylphenol-formaldehyde resin coating with the coated sides in contact and typed with a typewriter. As a result, no detectable color change was found on the CF sheet. When the absorption characteristics of the recorded image were determined with a UV spectrometer, it absorbed strongly the near infrared region with an absorption maximum at 720 nm and no appreciable absorption was found in the visible region. Characteristically this recorded image could hardly be recognized by the eye but could be read with the OCR. The absorption characteristics of the recorded image are shown in Table 4. 
     Examples 105-118 
     Production of pressure-sensitive recording materials 
     The procedure of Example 104 was repeated except that the phthalide compounds listed below in Table 4 were respectively used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) to provide white CB sheets, which were then placed on CF sheets, respectively, and typed with a typewriter. Like the image obtained in Example 104, there was no apparent change in the color of the CF sheets and characteristically the images could hardly be identified by the eye but could be read with the OCR. The absorption characteristics of the respective recorded images are shown in Table 4. 
     Comparison Example 14 
     Production of a pressure-sensitive recording material 
     The procedure of Example 104 was repeated except that compound A as synthesized in Comparison Example of Synthesis-1 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) to provide a CB sheet, which was then superimposed on a CF sheet and typed. The recorded image obtained using compound A assumed a distinct green-blue color. The absorption characteristics of this recorded image are presented in Table 4. 
     Comparison Example 15 
     Production of a pressure-sensitive recording material 
     The procedure of Example 104 was repeated except that compound B as synthesized in Comparison Example of Synthesis-2 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) to provide a CB sheet, which was then superimposed on a CF sheet and typed. The recorded image obtained using compound B had a distinct green-blue color. The absorption characteristics of this recorded image are presented in Table 4. 
     
                       TABLE 4                                                     
______________________________________                                    
               Absorption characteristics of                              
               the recorded image on CF sheet.sup.1)                      
                            The region of                                 
                 Maximum    ≧80% absorbance                        
                 absorption relative to max                               
       Phthalide wavelength imum absorption                               
       compound No.                                                       
                 (nm)       (nm)                                          
______________________________________                                    
Example 104                                                               
         Compound 1  720        695-765                                   
Example 105                                                               
         Compound 13 725        690-755                                   
Example 106                                                               
         Compound 23 725        695-765                                   
Example 107                                                               
         Compound 41 725        695-755                                   
Example 108                                                               
         Compound 57 725        700-755                                   
Example 109                                                               
         Compound 70 735        705-775                                   
Example 110                                                               
         Compound 87 710        680-755                                   
Example 111                                                               
         Compound 89 705        660-760                                   
Example 112                                                               
         Compound 91 720        700-755                                   
Example 113                                                               
         Compound 92 720        790-750                                   
Example 114                                                               
         Compound 97 720        695-770                                   
Example 115                                                               
         Compound 98 720        690-760                                   
Example 116                                                               
         Compound 108                                                     
                     730        705-760                                   
Example 117                                                               
         Compound 144                                                     
                     725        680-785                                   
Example 118                                                               
         Compound 155                                                     
                     745        725-765                                   
Comparison                                                                
         Compound A  745        590-795                                   
Example 14                                                                
Comparison                                                                
         Compound B  735        590-785                                   
Example 15                                                                
______________________________________                                    
 .sup.1) CF sheet: zincmodified poctylphenol-formaldehyde resin           
 
    
     Example 119 
     Production of a pressure-sensitive recording material 
     In 47 g of KMC-113 were dissolved 1.5 g of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and 1.5 g of 2-anilino-3-methyl-6-diethylaminofluorane with heating. On the other hand, 5 g of a system modifier (SM-100) was added to 100 g of water and the mixture was adjusted to pH 4 with aqueous sodium hydroxide solution. To this were added the solution prepared above and 10 g of melamine-formaldehyde precondensate (UMC-300) and the mixture was emulsified with a homo-mixer until the size of oil droplets became 4 microns. This emulsion was heated to 60° C. with stirring and further stirred for 1 hour. After cooling to ambient temperature, the emulsion was adjusted to pH 7.5 with 25% aqueous ammonia to provide a micro-encapsulated color former dispersion. 
     Ten (10) grams of the microcapsule dispersion was mixed with 2 g of wheat starch and 1 g of latex and the composition was coated in a coverage of 5 g solids/m 2  on a sheet of wood-free paper weighing 50 g/m 2  to provide a CB sheet. 
     The CB sheet thus prepared was superimposed on a CF sheet coated with zinc-modified p-octylphenol-form-aldehyde resin with the coated sides in contact with each other and typed with a typewriter, whereupon a distinct black image was recorded on the CF sheet. This recorded image could be read with the OCR. 
     Examples 120-134 
     Production of pressure-sensitive recording materials 
     The procedure of Example 119 was repeated except that the phthalide compounds listed below in Table 5 were respectively used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide and the fluorane compounds mentioned in Table 5 were respectively used in lieu of 2-anilino-3-methyl-6-diethylaminofluorane to provide white CB sheets. Each of the CB sheets was placed on a CF sheet and typed with a typewriter. The recorded images thus obtained were invariably distinct black and could be read with the OCR. 
     
                       TABLE 5                                                     
______________________________________                                    
                         Phthalide                                        
       Fluorane compound compound No.                                     
______________________________________                                    
Example 120                                                               
         2-Anilino-3-methyl-6-(N-ethyl-N-                                 
                             Compound 1                                   
         isobutylamino)fluorane                                           
Example 121                                                               
         2-Anilino-3-methyl-6-(N-ethyl-N-                                 
                             Compound 1                                   
         isopentylamino)fluorane                                          
Example 122                                                               
         2-(2,4-Dimethylanilino)-3-methyl-                                
                             Compound 13                                  
         6-diethylaminofluorane                                           
Example 123                                                               
         2-(2,6-Diethylanilino)-3-methyl-                                 
                             Compound 13                                  
         6-diethylaminofluorane                                           
Example 124                                                               
         2-(2,6-Dimethylanilino)-3-methyl-                                
                             Compound 41                                  
         6-diethylaminofluorane                                           
Example 125                                                               
         2-(3-Methylanilino)-3-methyl-6-                                  
                             Compound 57                                  
         diethylaminofluorane                                             
Example 126                                                               
         2-(2,4-Dimethylanilino)-3-methyl-                                
                             Compound 57                                  
         6-diethylaminofluorane                                           
Example 127                                                               
         2-Anilino-3-methyl-6-(N-methyl-                                  
                             Compound 70                                  
         N-cyclohexylamino)fluorane                                       
Example 128                                                               
         2-Anilino-3-chloro-6-diethyl-                                    
                             Compound 70                                  
         aminofluorane                                                    
Example 129                                                               
         2-Anilino-3-methyl-6-(N-ethyl-N-                                 
                             Compound 89                                  
         isobutylamino)fluorane                                           
Example 130                                                               
         2-(2,4-Dimethylanilino)-3-methyl-                                
                             Compound 92                                  
         6-diethylaminofluorane                                           
Example 131                                                               
         2-(2,6-Dimethylanilino)-3-methyl-                                
                             Compound 97                                  
         6-diethylaminofluorane                                           
Example 132                                                               
         2-(2,4-Dimethylanilino)-3-methyl-                                
                             Compound 98                                  
         6-diethylaminofluorane                                           
Example 133                                                               
         2-Anilino-3-chloro-6-                                            
                             Compound 108                                 
         diethylaminofluorane                                             
Example 134                                                               
         2-Anilino-3-methyl-6-(N-ethyl-N-                                 
                             Compound 144                                 
         tetrahydrofurfurylamino)fluorane                                 
______________________________________                                    
 
    
     Example 135 
     Production of a thermo-sensitive recording material 
     Using a sandmill, 5.0 g of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) was pulverized in the presence of 45 g of 2.5% aqueous poly(vinyl alcohol) solution until a mean particle size of 1 μm was attained to provide a dispersion. 
     On the other hand, 10 g of bisphenol A and 10 g of p-benzylbiphenyl were pulverized in the presence of 80 g of 2.5% aqueous polyvinyl alcohol solution in a sandmill until a mean particle size of 1 μm was attained to provide a dispersion. 
     The two dispersions prepared above were thoroughly blended with 30 g of 50% calcium carbonate dispersion and 15 g of 30% paraffin wax dispersion to provide a thermo-sensitive coating. 
     This thermo-sensitive coating was coated in a coverage of 5 g (solids)/m 2  on a sheet of wood-free paper weighing 50 g/m 2 , dried and calendered until the Bekk smoothness value of the thermo-sensitive recording layer being 200 seconds to provide a white thermo-sensitive recording material. 
     Using a TH-PMD printer (manufactured by Ohkura Electric Machinery Co., Ltd.), the above thermo-sensitive recording material was developed at a pulse width of 1.15 ms and the optical density (OD value) of the image was measured on Macbeth RD-914 (filter: Visual). The absorption characteristics of the image thus obtained were also determined on Spectrophotometer UV365 (manufactured by Shimadzu Corporation). The results are shown in Table 6. This image record could hardly be read with the eye but could be read with the OCR. 
     Examples 136-146 
     Production of thermo-sensitive recording materials 
     The procedure of Example 135 was repeated except that the phthalide compounds listed below in Table 6 were respectively used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) to provide white thermo-sensitive recording materials, which were then tested as in Example 135. The results are presented in Table 6. 
     The image records obtained were hardly legible to the eye but could be read with the OCR. 
     Comparison Example 16 
     Production of a thermo-sensitive recording material 
     The procedure of Example 135 was repeated except that compound A as produced in Comparison Example of Synthesis-1 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) to provide a white thermo-sensitive recording material, which was then tested as in Example 135. The results are presented in Table 6. 
     This image record was green-blue. 
     Comparison Example 17 
     Production of a thermo-sensitive recording material 
     The procedure of Example 135 was repeated except that compound B as synthesized in Comparison Example of Synthesis-2 was used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) to provide a white thermo-sensitive recording material, which was then tested as in Example 135. The results are presented in Table 6. 
     This recorded image was green-blue. 
     
                       TABLE 6                                                     
______________________________________                                    
                   Absorption                                             
                   characteristics                                        
                   of the recorded image                                  
                 Deve-             The region                             
                 loped             of ≧80%                         
                 color   Maximum   absorbance                             
                 image   absorp-   relative to                            
                 den-    tion wave-                                       
                                   maximum                                
       Phthalide sity    length    aborption                              
       compound No.                                                       
                 (OD)    (nm)      (nm)                                   
______________________________________                                    
Example 135                                                               
         Compound 1  0.13    725     690-760                              
Example 136                                                               
         Compound 13 0.10    720     695-750                              
Example 137                                                               
         Compound 70 0.07    725     695-765                              
Example 138                                                               
         Compound 87 0.24    695     640-750                              
Example 139                                                               
         Compound 89 0.28    690     615-745                              
Example 140                                                               
         Compound 91 0.08    725     695-760                              
Example 141                                                               
         Compound 92 0.14    725     690-760                              
Example 142                                                               
         Compound 97 0.12    720     675-765                              
Example 143                                                               
         Compound 98 0.14    720     680-765                              
Example 144                                                               
         Compound 108                                                     
                     0.12    730     695-765                              
Example 145                                                               
         Compound 144                                                     
                     0.28    720     645-785                              
Example 146                                                               
         Compound 155                                                     
                     0.27    740     695-780                              
Comparison                                                                
         Compound A  0.55    740     575-795                              
Example 16                                                                
Comparison                                                                
         Compound B  0.57    730     590-780                              
Example 17                                                                
______________________________________                                    
 
    
     Example 147 
     Production of a thermo-sensitive recording material 
     Using a sandmill, 2.5 g of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and 2.5 g of 2-anilino-3-methyl-6-di-n-butylaminofluorane were pulverized in the presence of 45 g of 2.5% aqueous poly(vinyl alcohol) solution until a mean particle size of 1μ was attained to provide a dispersion. 
     On the other hand, 10 g of bisphenol A and 10 g of p-benzylbiphenyl were comminuted in the presence of 80 g of 2.5% aqueous poly(vinyl alcohol) solution until a mean particle size of 1 μm was attained to provide a dispersion. 
     The two dispersions prepared above were thoroughly blended with 30 g of 50% calcium carbonate dispersion and 15 g of 30% paraffin wax dispersion to prepare a thermo-sensitive coating. This thermo-sensitive coating was coated in a coverage of 5 g (solids)/m 2  on a sheet of wood-free paper weighing 50 g/m 2 , dried and calendered until the Bekk smoothness of the thermo-sensitive recording layer being 200 seconds to provide a white thermo-sensitive recoding layer. 
     When this heat-responsive recording material was typed with the TH-PMD printer, a black recorded image was obtained. This image could be read with the OCR. 
     Examples 148-165 
     Production of thermo-sensitive recording materials 
     The procedure of Example 147 was repeated except that the phthalide compounds listed below in Table 7 were respectively used in lieu of 3-[1-(1-ethyl-2-methylindol-3-yl)-1-(4-methylphenyl)ethylen-2-yl]-3-(4-diethylaminophenyl)phthalide (compound 1) and the fluorane compounds listed in Table 7 were respectively used in lieu of 2-anilino-3-methyl-6-di-n-butylaminofluorane to provide white thermo-sensitive recording materials, which were then typed with the TH-PMD printer. 
     The recorded images thus obtained were distinct black and could be read with the OCR. 
     
                       TABLE 7                                                     
______________________________________                                    
                         Phthalide                                        
       Fluorane compound Compound No.                                     
______________________________________                                    
Example 148                                                               
         2-Anilino-3-methyl-6-(N-ethyl-                                   
                             Compound 1                                   
         N-isobutylamino)fluorane                                         
Example 149                                                               
         2-Anilino-3-methyl-6-(N-ethyl-                                   
                             Compound 1                                   
         N-isopentylamino)fluorane                                        
Example 150                                                               
         2-(2,4-Dimethylanilino)-3-methyl-                                
                             Compound 1                                   
         6-diethylaminofluorane                                           
Example 151                                                               
         2-(2,6-Diethylanilino)-3-methyl-                                 
                             Compound 13                                  
         6-diethylaminofluorane                                           
Example 152                                                               
         2-(2,6-Dimethylanilino)-3-methyl-                                
                             Compound 13                                  
         6-diethylaminofluorane                                           
Example 153                                                               
         2-(3-Methylanilino)-3-methyl-                                    
                             Compound 13                                  
         6-diethylaminofluorane                                           
Example 154                                                               
         2-(2,4-Dimethylanilino)-3-methyl-                                
                             Compound 57                                  
         6-diethylaminofluorane                                           
Example 155                                                               
         2-Anilinl-3-methyl-6-(N-methyl-                                  
                             Compound 57                                  
         N-cyclohexylamino)fluorane                                       
Example 156                                                               
         2-Anilino-3-chloro-6-                                            
                             Compound 57                                  
         diethylaminofluorane                                             
Example 157                                                               
         2-Anilino-3-methyl-6-(N-ethyl-                                   
                             Compound 87                                  
         N-isobutylamino)fluorane                                         
Example 158                                                               
         2-Anilino-3-methyl-6-(N-ethyl-                                   
                             Compound 89                                  
         N-isopentylamino)fluorane                                        
Example 159                                                               
         2-Anilino-3-methyl-6-di-n-                                       
                             Compound 91                                  
         pentylaminofluorane                                              
Example 160                                                               
         2-(3-Methylanilino)-3-methyl-                                    
                             Compound 92                                  
         6-diethylaminofluorane                                           
Example 161                                                               
         2-(3-Methylanilino)-3-methyl-6-                                  
                             Compound 97                                  
         di-n-butylaminofluorane                                          
Example 162                                                               
         2-Anilino-3-methyl-6-(N-methyl-                                  
                             Compound 98                                  
         N-n-propylamino)fluorane                                         
Example 163                                                               
         2-Anilino-3-methyl-6-(n-ethyl-                                   
                             Compound 108                                 
         N-ethoxypropylamino)fluorane                                     
Example 164                                                               
         2-(2-Chloroanilino)-6-                                           
                             Compound 144                                 
         diethylaminofluorane                                             
Example 165                                                               
         2-(2-Chloroanilino)-6-(di-n-                                     
                             Compound 155                                 
         butylamino)fluorane                                              
______________________________________                                    
 
    
     EFFECT OF THE INVENTION 
     The near infrared absorber employing the phthalide compound of this invention and the recorded image obtainable with the recording material of this invention absorb strongly the near infrared region but only slightly the visible region. Therefore, the near infrared absorber of this invention is either colorless or pale in color to the eye but has a large capacity to absorb near infrared radiation and the recorded image obtainable with the recording material of this invention is hardly legible to the eye but can be read with an OCR. Moreover, in the recording material employing the phthalide compound of this invention in combination with other conventional color formers, the influence of the compound on the color of the other color formers is minimal.