Triazolium salt photoreductive imaging
United States Patent Bailey et al.  
 [ 1 Apr. 29, 1975 [75] Inventors: David S. Bailey; Michael D. Shea,  
 both of Rochester, NY  
 [73] Assignee: Eastman Kodak Company,  
 Rochester, N.Y.  
 [22] Filed: Aug. 2, I973 [2!] Appl. No.: 384,860  
 [52] US. Cl 96/48 R; 96/88; 96/75; 96/76 R; 96/90 R; 96/49 [5 1] Int. Cl. G03c 5/24; G03c H52 [58] Field of Search 96/48 R, 90 R, 88, 49, 9619i R, 75, 76 R, 29  
 [56] Relerences Cited UNITED STATES PATENTS 3,l85 567 5/1965 R0gcrs.. 96/29 3,257,205 6/1966 Cassicrs, et al. 96/29 FOREIGN PATENTS OR APPLICATIONS 670.883 4/1972 United Kingdom 96/48 908299 10/1962 United Kingdom 96/48 Primary Examiner-Won H. Louie, Jr. Attorney, Agent, or Firm-D. M. Schmidt [57] ABSTRACT A triazolium salt capable of reduction to an azo-amine dye is present in a radiation-sensitive layer in combination with a photoreductant capable of producing, in the presence of labile hydrogen atoms. a reducing agent precursor in radiation-struck areas of the layer. An image is produced in the layer by bringing the layer into contact with an alkaline medium after imagewise exposure to actinic radiation.  
 46 Claims, No Drawings TRIAZOLIUM SALT PHOTOREDUCTIVE IMAGING This invention relates to an improved photographic element which exhibits low, stable background densities without fixing and to a process for recording im ages therewith. In a specific aspect, this invention is di&#39; rected to an improved photographic element and to a process for its use in which a visible azo-amine dye is selectively produced from an azo-amine dye precursor in image areas, while the background areas remain stable and of low optical density in the presence of actinic radiation and without removal or alteration of the amamine dye precursor.  
  It is well known in the photographic arts to record images by incorporating within a radiation-sensitive layer of a photographic element a dye precursor of low optical density capable of conversion to a visible dye. In order to avoid dye printout in background areas after exposure it is conventional practice to inactivate and/or wash out the dye precursor. Where the dye is formed by oxidation of its precursor there is frequently a problem with background printout attributable to atmospheric oxidation of the dye precursor remaining in the background areas. The loss of contrast is, of course, further accelerated if the dye itself also tends to fade.  
  The reduction of triazolium salts to form azo-amine dyes is generally well known in the art. Photographic systems incorporating such dyes are disclosed, for example, in French Pat. No. 998,055, published Jan. 14, 1952; in U.S. Pat. No. 3,185,567, issued May 25,1965; and in U.S. Pat. No. 3,257,205, issued June 21, 1966.  
  The French Patent noted above teaches the direct re duction of triazolium salt to an azo-amine dye upon exposure to ultraviolet light in the presence ofa mild acid or alkali. If re-exposure to ultraviolet light is to occur, fixing is required to prevent background printout. It would apparently be necessary to resort to washing out the unreduced triazolium salt to insure against printout.  
  Each of the U.S. patents noted above contemplates the use of a silver halide emulsion layer in combination with a separable element incorporating a triazolium salt. U.S. Pat. No. 3,185,567 teaches modifying a conventional silver halide emulsion layer containing photographic element by incorporating a developer and in an adjacent, separable image-receiving layer a triazolium salt. The developer is initially confined to a rupturable pod. After exposure the developer is released to form a silver image in the emulsion layer. The developer that is not expended in forming the silver image migrates into the image-receiving layer and reduces the triazolium salt to form a complementary image. The teaching of U.S. Pat. No. 3,257,205 is generally similar, except that a heat responsive developer is employed. In both of these patents a comparatively complex, multilayer, silver halide emulsion containing photographic element is required in order to obtain an azo-amine dye image.  
  The following copending, commonly assigned patent applications can be usefully considered in conjunction with the present invention: .I. C. Fleming, 1. W. Manthey and R. T. Brongo applications Ser. Nos. 384,859 and 384,861, titled TETRAZOLIUM SALT PHO- TOREDUCTIVE IMAGING and PHOTOGRAPHIC ELEMENTS AND PROCESSES FOR INCORPO- RATED HYDROGEN SOURCE PHOTOREDUC- TION IMAGING, respectively, as well as D. S. Bailey application Serial No. 384,858, titled PHOTO- GRAPHIC ELEMENTS AND PROCESSES FOR PRODUCING FORMAZAN DYE IMAGES OF EN- HANCED STABILITY, each filed concurrently herewith.  
  It is an object of this invention to provide the capability of producing an azo-amine dye image employing a photographic element that can be comprised of only a single imaging layer, that does not require the use of silver halide, that can be processed in a dry state, and that does not require fixing prior to re-exposure to actinic radiation.  
  It is a further object to provide such a photographic element that can exhibit relatively low, stable background densities and that possesses an image add-on capability.  
  It is a still further object to provide such a photographic element that, as compared with analogous tetrazolium salt containing photographic elements, can be easier to prepare, can produce images that are more nearly neutral in hue and that can be less susceptible to yellowing during storage after exposure.  
  It is another object to provide a process for using such photographic elements which requires only image exposure followed by a single processing step, which can be performed in a dry state.  
  In one aspect this invention is directed to a photographic element having a support and at least one radiation-sensitive image recording layer. The image recording layer is comprised of a triazolium salt capable of reduction to an azo-amine dye and a photoreductant capable of producing a base activatible reducing agent precursor on exposure to actinic radiation in the presence of labile hydrogen atoms.  
  In another aspect this invention is directed to an image recording process comprising converting a photoreductant within a selected areal portion of a radiationsensitive layer of a photographic element to a reducing agent precursor. Conversion of the photoreductant to the reducing agent precursor is accomplished by imagewise exposing the photoreductant to actinic radiation in the presence of labile hydrogen atoms. Thereafter the precursor is activated with a base to form a reducing agent which in turn reduces triazolium salt present within the selected areal portions containing the reducing agent to azo-amine dye.  
  In a specifically preferred embodiment of the invention a triazolium salt capable of reduction to form azoamine dye and a photoreductant are associated within a binder in the presence of a source of labile hydrogen atoms and coated onto a conventional photographic support to form a radiation-sensitive image recording layer. The resulting photographic element is then exposed image-wise to actinic radiation. Actinic radiation in this case is radiation in the ultraviolet and/or visible spectrum--that is, electromagnetic radiation of less than 700 nm in wavelength and, preferably, below 500 nm. Exposure causes the photoreductant to form a latent image in the radiation-struck areas of the image recording layer. In latent image formation the photoreductant is converted to a reducing agent precursor which, in turn, can be readily converted to a reducing agent in the presence of a base.  
  While Applicants do not wish to be bound by any particular theory as to how the photoreductant forms the latent image, it is believed that one or more of the labile hydrogen atoms present in the image recording layer chemically bond to the photoreductant at a radiation-sensitive site within photoreductant molecule. As formed, the reducing agent precursor generated by the radiation-struck photoreductant is incapable of directly reducing the triazolium salt to produce an azo-amine dye. However, when the exposed radiation-sensitive layer is treated with a base, preferably gaseous ammonia, the reducing agent precursor is converted to an ac tive reducing agent which reacts with the triazolium salt to form an azo-amine dye.  
  It is a specific advantage that the exposed imagebearing photographic elements of this invention can be re-exposed to actinic radiation without fixing. The rea&#39; son for this is that, while the remaining photoreductant will form a second latent image in the background areas when the photographic element is re-exposed, this does not interfere with seeing the existing visible image, The photoreductant is specifically chosen to yield a reducing agent precursor that is light in color and, preferably, is substantially colorless, so that a sharp visible contrast exists between the azo-amine dye image and the background areas.  
  It is another distinct advantage of the photographic elements of this invention that they exhibit stable, low density backgrounds when stored in the atmosphere over extended periods. Further, the backgrouns show less tendency to yellow with age than comparable elements containing tetrazoiiurn salts, Since the atmosphere is free of basic substances, the reducing agent precursor is not converted to a reducing agent during storage ofthe photographic element in contact with the atmosphere. Similarly, there is no direct atmospheric reduction of the triazolium salt on storage of the photographic elements. Over an extended period of time atmospheric oxygen can oxidize the latent image of reducing agent precursor, thereby entirely eliminating the possibility of unwanted image formation. Thus, in marked contrast to photographic elements that contain dye precursors which form visible dyes on oxidation, the photographic elements of the present invention are notably free of background printout.  
  Whereas in classical photography a succession of developing, stopping. fixing and rinsing baths are typically used in the course of forming a stable photographic record, it is a significant feature of this invention that wet processing of the photographic element is not required. While it is recognized that the reducing agent precursor could. if desired, be brought into contact with a basic solution for conversion to a reducing agent, according to the preferred practice of this invention the reducing agent precursor is contacted with gaseous ammonia to produce the active reducing agent. in one form the gas eous ammonia can be generated in situ&#34;. Beyond this, in the image recording layer each of the components and each of the reaction products formed, except for the azo-amine dye. are of low optical density. This avoids any need for rinsing or processing baths to remove or alter any of the components or reaction products formed within the imagerecording layer.  
  Since the single processing step of exposure to gaseous ammonia can be performed in commercially available equipment sold for this purpose and since no resort to comparatively cumbersome conventional photographic processing techniques, such as processing baths, uniform or image area heating, volatilizing components and the like, is required, it is apparent that the photographic elements of the present invention are advantageously simple and convenient to use.  
  This invention can be practiced utilizing any triazolium salt which on reduction forms an azo-amine dye of a detectibly different color. A wide variety of such triazolium salts are known to the art including bistriazolium salts linked directly or through intervening divalent radicals.  
  To be useful in the practice of this invention it is required only that the triazolium salt incorporated into the image-forming layer undergo a detectable color change upon reduction to the corresponding dye. Since the azo-amine dyes exhibit higher optical densities than their parent triazolium salts, they produce a sharp visible contrast with background areas. lt is a distinct advantage of this invention that triazolium salts are readily available in colorless form and tend to remain colorless in background areas during storage of the photographic elements. The transparency of the triazolium salts, of course, enhances the contrast that can be achieved both initially and after storage. Further, aesthetic considerations frequently dictate that white or transparent backgrounds be available for many photographic applications. Also of importance is that the azo-amine dyes produced by the triazolium salts of this invention can be chosen to provide any one of a wide variety of colors, and, most importantly, images of neutral hue can be formed by the azo-amine dyes. Hence, it is possible for the photographic elements of this invention to provide readily neutral hue images on transparent or white backgrounds, as is most desirable for many recording applications. Finally, the azo-amine dye images produced are generally more stable than comparable formazan dye images.  
  The triazolium salts preferred for the practice of this invention are those having an aromatic ring fused with the triazole nucleus. Such triazolium salts produce azoamine dyes of increased density as compared to triazolium salts lacking a fused aromatic ring. Further, these latter triazolium salts typically produce az0- amine dyes of a yellow hue, whereas triazolium salts containing an aromatic ring fused with the triazole nucleus are typically either shifted toward the red portion of the spectrum or more neutral in hue.  
  The triazolium salts which are most preferred for use in the practice of this invention are those which exist in the tautomeric forms indicated below:  
 N I N h Z t \N IN N RfiH &#34;W g I y wherein Z is comprised of the atoms necessary to complete a fused, aromatic ring structure; y is l to 2; R is an aromatic or aromatic-like heterocyclic group; R&#39; is an aromatic substituent, an aromatic-like heterocyclic substituent or an alkyl group having from l to 20 carbon atoms, preferably l to 6 carbon atoms and X is an anion.  
  As employed herein the term aromatic-like heterocyclic substituent&#34; is defined as a substituent group including a 5 or 6 member ring structure having conju gated unsaturation and containing in addition to carbon atoms in the ring structure at least one atom selected from the group consisting of nitrogen, oxygen and sulfur. Exemplary of such aromatic-like heterocyclic substituents are pyridyl, oxazolyl, thiazolyl, quinolinyl, benzoxazolyl, benzothiazolyl and similar substitufills.  
  In a specific preferred form of the invention Z is chosen to form a benzotriazole, naphthol l,2-d]triazole or naphtho[2,3-d]triazole nucleus. Generally triazolium salts containing naphthotriazole nuclei are preferred over those containing benzotriazole nuclei. When y is 2, R is preferably an arylene group--e.g., a phenylene, bisphenylene, naphthalene, anthrylene, etc. When y is l, R is preferably an aryl group. R is preferably an aryl or aromatic-like heterocyclic group.  
  It is recognized that R, R&#39; and Z can include a variety of ring substituents. Exemplary of specifically contemplated ring substituents are low alkyl (i.e., one to six carbon atoms), lower alkenyl (i.e., two to six carbon atoms), lower alkynyl (i.e., two to six carbon atoms), benzyl, styryl, phenyl, biphenyl, naphthyl, alkoxy (e.g., methoxy, ethoxy, etc), aryloxy (e.g., phenoxy), carboalkoxy (e.g., carbomethoxy, carboethoxy, etc.), carboaryloxy (e.g., carbophenoxy, carbonaphthoxy), acyloxy (e.g., acetoxy, benzoxy, etc.), acyl (e.g., acetyl, benzoyl, etc.), halogen (i.e., fluoride, chloride, bromide, iodide), cyanide, azide, nitro, haloalkyl (e.g., trifluoromethyl, trifluoroethyl, etc. amino (e.g., dimethylamino), amido (e.g., acetamido, benzamido), ammonium (e.g., trimethylammonium), azo (e.g., phenylazo), sulfonyl (e.g., methylsulfonyl, phenylsulfonyl), sulfoxide (e.g., methylsulfoxide), sulfonium (e.g., dimethyl sulfonium), silane (e.g., trimethylsilane) and thioether (e.g., methyl mercaptide) substituents. While these and other substituents can be chosen to advantage to influence image densities, ease of reduction, dye color and stability, etc, the capability of a triazolium salt to be reduced to an aZo-amine dye is in general controlled by the triazole nucleus configuration rather than the substituents chosen. To enhance the stability of the azo-amine dyes produced it is preferred to incorporate within the triazolium salts of this inven tion predominantly electronegative substituents.  
  Any anion known to be useful in azo-amine dye forming triazolium salts can be used in the practice of this invention. Preferred anions are those set forth in Table I. Any one of these anions can be incorporated in place of any other anion in any of the triazolium salts set forth in Table I. Non-basic, non-nucleophilic anions are preferred, such as tetrafluoroborate and hexafluorophosphate, for example. Such anions provide the resulting triazolium salt with enhanced protection against anion induced reduction, and for this reason their use is preferred.  
  It is recognized that the color of the azo-amine dyes can be influenced by the incorporation of various metal salts in combination with the triazolium salt. Salts of metals such as iron, nickel, cobalt, copper, zinc, cadmium, chromium, titanium molybdenum or tungsten are useful for this purpose. It is also recognized that such metal salts can be used in the practice of this in-- vention for the purpose of chelating the azo-amine dye produced on exposure to thereby further stabilize the dye against subsequent fading. All azo-amine dyes are capable of forming at least bidentate chelates. While distinct stabilization can be achieved with bidentate and tridentate chelates, the use of triazolium salts that form tridentate chelates gives greater stabilization and is preferred. Exemplary of triazolium salts capable of forming tridentate azo-amine dye chelates are those having one or more N-heterocyclic aromatic rings in the l or 2 position, such as Z-pyridyl and 2-azolyl (e.g., Z-thiazolyl, Z-benzothiazolyl, 2-oxazolyl, 2- benzoxazolyl, etc.) ring structures, for example.  
  If a metal salt is incorporated within the imaging layer for the purpose of chelating, some increase in background density can occur upon prolonged reexposure to actinic radiation, unless the residual photoreductant, the remaining chelating metal salt, the unreduced triazolium salt or all of these are removed from the non-image areas. This can be accomplished, for example, by washing the photographic element in a suitable solvent, such as a polar solvent, like water, which does not attack or leach the azo-amine dye. To obtain minimal background densities and to avoid processing the photographic element after image formation, it is preferred to utilize triazoliam salts with electronegative substituents that produce stabilized azo-amine dyes rather than to incorporate chelating metal salts. Where extended re-exposure to actinic radiation is not contemplated or where increasing background densities can be tolerated, the azo-amine dyes can be chelated and the photoreductant, the triazolium salt and the unreacted metal salt in the background areas can be left in the photographic element. In other words, processing after image formation can be omitted.  
  Exemplary preferred triazolium salts useful in the practice of this invention are set forth below in Table I:  
 T- l 4 dil 2-( 2,3,4,S-Ietrachlorophcnyl ]-3-phenyllHmaphthol l .2-dI-l ,2.3-triazolium] tctrachlorozincate T-l 5 24 4-fluoro&#39;4biphenyl I-B-phenyl-ZH- naphthol 1,2-dll ,2,3-lria7olium chloride T-lb 2-(4-cyano-l-naphthyl )3-phcnyl-ZH- naphthol [.ldl-l ,ZZJ-triauolium bromide T l 8 2-( 2,4-dinitrophenyl )J-phcnyl-ZH naphthol LZ-dll ,lltriazolium tetrafluoroboratc Exemplary Preferred Triazolium Salts for Forming Azo-Aminc Dyes r-zo  Procedures for preparing triazolium salts useful in the practice of this invention are known in the art. Exemplary of known preparative techniques are those disclosed by Krollpfeiffer, Mulhausen and Wolf, Annalen, 508, 39, (1933); Begtrup and Poulsen, Aera Chem. Scand. 25, 2096 (1971); and Charrier and Beretta, Gazzella Chimica Italiana, 53, 773 (1923) as well as the French patent above noted.  
  As employed herein, the term photoreductant&#34; designates a material capable of molecular photolysis or photo-induced rearrangement to generate a reducing agent precursor. The term &#34;reducing agent precursor&#34; designates a compound which is not capable of reducing a triazolium salt employed in combination therewith, but which can be activated by a base to become a reducing agent capable of reducing the triazolium salt.  
  Exemplary of the photoreductants which can be utilized in the practice of this invention are disulfides capable of being photolytically cleaved at the 8-8 bond to form a mercaptan in the presence of labile hydrogen atoms. A variety of such disulfides are known in the art. it is preferred to employ hydrocarbon disulfides and, more specifically. aryl disulfides. The aryl disulfides preferred are the alkyl aryl disulfides having from l to (preferably 1 to 6) alkyl carbon atoms and diaryl disulfides. Either single or fused aromatic ring structures can be employed--e.g. phenyl, naphthyl, anthryl and similar ring structures. It is also contemplated that aromatic disulfides that incorporate non-basic heterocyclic aromatic rings can be utilized. Typical of such disulfides are those incorporating 5 and 6 membered aromatic rings having oxygen and/or sulfur heteroatoms.  
  In addition to the disulfides set forth above, phenazinium salts can be utilized as photoreductants in the practice of this invention. Also useful as photoreductants are diazoanthrones, B-ketosulfides and nitroarenes. The arene ring can be any aromatic carbocyclic ring structure--e.g. phenyl, naphthyl, anthryl and similar ring structures. It is specifically contemplated that the nitroarenes can incorporate substituents having labile hydrogen atoms and that these labile hydrogen atoms can be used in converting the photoreductant to a reducing agent precursor. For example, the nitroarenes can incorporate hydroxyalkyl substituents to provide labile hydrogen atoms.  
  Specific exemplary disulfides, phenazinium salts, diazoanthrones, B-ketosulfides and nitroarenes are set forth in Table ll.  
 TABLE II Exemplary hotoreductants PR- Q-nitrobenzyl alcohol PR- 2 4bromonitrobenzene PR- 3 2-4 l-hydroxyethyl)- l -nitronaphthalene PR- 4 Z-nitroanthracene PR- 5 4-hcxoxynitrobenzcnc Pr- 6 2.S-diethoxynitrobenzene PR- 7 Z-nitronaphthalcnc PR- 8 2-cthoxy-l-nitronaphthalcne PR 9 Z-isopropylnitrobcnzcnc Pr- 1U Z-benzylnitrohenzene Pr-l l l-methyl-4-nitropyridinium tetrafluoroborate PR- 1 2 l-naphthyl-l &#39;-phcnethyl disulfidc Pr-l 3 B-naphthyl disulfide Pr-l4 Q-anthryl disulfide Pr-lb diphenylmethyl Z-naphthyl disulfide Pr- I 8 4.4&#39;-dihexyldiphenyl disulfidc Pr- 1 9 2.2&#39;-bis( hydroxymethyl )diphenyl disulfide PR-ZO 4,4&#39;-dinitrodiphenyl disulfidc PR-2l 3-phenyL3H-nuphthol l.2-c]-l.2-dithiole PR-22 phenazinium 4-loluenesulfonate PR-Zl N-methyl phenazinium bromide PR-24 Z-methoxyphcnazinium hexafluorophosphate PR-Zfi 2-nitrophenazinium tetrafluoroborate PR-Zfi l-(hydroxymethyl)phenazinium chloride PR-27 l-isn ropoxy-lO-methylphenazinium tetra uoroborate PR-2B 2,3,9-trimethylphenazinium chloride PR-Z) 2,3-dimcthyl-5-nitrophenazinium methyl sulfate PR-30 2.3-dichlorophcnazinium chloride PR-3I Z-cyanophenazinium tetrafluorobomle PR-32 l,2-benzophcnazinium 4-toluenesulfonatc PR-33 lO-diazoanlhrone PR-34 2-methoxy- I 0-diazoanthrone PR-35 3-nitrol0diazoanthrone PR-36 3 .b-diethoxyl 0-diazoanthrone PR 3 7 3chlorol O-diazoanthrone PR-3 8 4ethoxy- I O-diazoanthrone Pit-3) 4-( l-hydroxyethyl l-lO-diazoanthrone PR-4O 2.7-diethyll O-diazoanthrone PR4] 2-( 4-tolyl )thiochromanone PR-42 7-methyl-2-tolylthiochromanone PR-43 2-(2.4.6-trimethylphenylthioJ- l -tet ral one PR-44 Z-hcnzylthir. l -tetralone PR-45 Z-l 4-tolyl )thiol -tetralone PR-46 4-tolylthioacctone PR-47 3-phenyl-2-( Holy-I )thiopropiophenone PR-48 2-ethylthio-3-phenylpropiophenone PR4) 3-phenyl-2-phenylthiopropiophenone Pr-SO 3-phenyll 4-tolyl )thio-2 propionaphthone PR-S l 4&#39;-methoxy-3phenyl-2-phenylthiopropiophenone PR-SZ 3.3-diphcnyl-2-phenylthiopropiophenone Quinones are useful as photoreduetants in the practice of this invention. Useful quinones include ortho and para-benzoquinones, diphenoquinones, ortho and para-naphthoquinones, phenanthrenequinones and anthraquinones. The quinones may be unsubstituted or incorporate any substituent or combination of substituents that do not interfere with the conversion of the quinone to the corresponding reducing agent precursor-cg. hydroquinone. A variety of such substituents are known to the art and include, but are not limited to, primary, secondary and tertiary alkyl, alkenyl and alkynyl, aryl, alkoxy, aryloxy, aralkoxy, alkaryloxy. hydroxyalky], hydroxyalkoxy, alkoxyalkyl, acyloxyalkyl, aryloxyalkyl. aroyloxyalkyl, aryloxyalkoxy, alkylcarbonyl, carboxyl, primary and secondary amino, aminoalkyl, amidoalkyl, anilino, piperidino, pyrrolidino, morpholino, nitro, halide and other similar substituents. Such aryl substituents are preferably phenyl substituents and such alkyl, alkenyl and alkynyl substituents, whether present as sole substituents or present in combination with other atoms, typically incorporate twenty (preferably six) or fewer carbon atoms.  
  Specific exemplary quinones intended to be used in combination with a separate source of labile hydrogen atoms are set forth in Table lll.  
 TABLE III Exemplary Quinones Useful with External Hydrogen Source naphthoquinone Any conventional source of labile hydrogen atoms that is not otherwise reactive with the remaining components or their reaction products contained within the photographic element can be utilized. Generally preferred for use are organic compounds having a hydrogen atom attached to a carbon atom to which a substituent is also attached which greatly weakens the carbon to hydrogen bond, thereby rendering the hydrogen atom labile. Preferred hydrogen source compounds are those which have a hydrogen atom bonded to a carbon atom to which is also bonded the oxygen atom of an oxy substituent and/or the trivalent nitrogen atom of an amine substituent. As employed herein the term amine substituent&#34; is inclusive of amide and imine substituents. Exemplary preferred substituents which produce marked lability in a hydrogen atom associated with a common carbon atom are oxy substituents, such as hydroxy, alkoxy, aryloxy. alkaryloxy and aralkoxy substituents and amino substituents, such as alkylarylamino, diarylamino, amido. N,N-bis(lcyanoalkyl)amino, N-aryl-N-(l-cyanoalkyl)amino, N- alkyl-N-( l-cyanoalkyhamino, N,N-bis( l-carbalkoxyalkyl)amino, N-aryl-N-(l-carbalkoxyalkyhamino, N-  
 alkyl-N-( l-carbalkoxyalkyhamino, N,N-bis-( lnitroalkyl)amino, N-alkyl-N-( l-nitroalkyl )amino, N-aryl-N-( l-nitroalkyUamino, N,N-bis( lacylalkyl)amino, N-alkyl-N-( l-acylalkyl)amino,  
 N-aryl-N-(l-acylalkyl)amino, and the like. The aryl substituents and substituent moieties are preferably phenyl or phenylene while the aliphatic hydrocarbon substituents and substituent moieties preferably incorporate twenty or fewer carbon atoms and, most preferably, six or fewer carbon atoms. Exemplary of compounds which can be used in the practice of this invention for the purpose of providing a ready source of labile hydrogen atoms are those set forth in Table IV. Compounds known to be useful in providing labile hydrogen atoms are also disclosed in US. Pat. No. 3,383,2l2, issued May 14, i968, the disclosure of which is here incorporated by reference.  
 TABLE IV Exemplary External Hydrogen Source Compounds HS- 1 poly(ethylcnc glycol) HS- 2 phcnyl-LZ-ethancdiol HS 3 nitrilotriacetonitrilc HS- 4 triethylnitrilotriacctatc HS- 5 poly(ethylene glycol] HS- 6 poly(vinyl butyral) HS- 7 polytvinyl acetal) HS- 8 l.4-bcnzenedimethanol HS- 9 methyl cellulose HS- l0 cellulose acetate butyrate HS-l l 2 2-bis(hydroxymethyl)-propionic acid HS-l2 l,3-bis-(hydroxymethyl)-urea HS-l3 4-nitrobenzyl alcohol HS-l4 4-methoxybenzyl alcohol HS-l5 2,4-dimethoxybenzyl alcohol HS-l6 3.4-dichlorophcnylglycol HS- l 7 N-( hydroxymcthyl J-benzamide HS-l 8 N-( hydroxymcthyl l-phthalimidc HS-l) 5-(hydroxymethyU-uracil hcmihydratc HS-2O nitrilotriacetic acid HS-Z l 2.2&#39;,2&#34;-tricthylnitrilotripropionate HS-ZZ 2,2&#39; 2&#34;-nitrilotriacctophenonc HS-23 polylvinyl acetate) HS-24 poly(vinyl alcohol) HS-25 eth l cellulose HS-26 car xymethyl cellulose HS-27 poly(vinyl formal) The compounds of Table IV capable of providing labile hydrogen atoms are referred to as external hydrogen source compounds. The external hydrogen source compounds are incorporated within the photographic elements of the present invention and can, in fact, perform more than one function. For example, the external hydrogen source polymers of Table N can also be used as binders as well as to provide a source of labile hydrogen atoms. These compounds are designated as external hydrogen source compounds only to point up that the labile hydrogen atoms are not incorporated in the photoreductant. As specifically noted above in connection with useful nitroarenes the photoreductants can themselves incorporate labile hydrogen atoms which facilitate their conversion to reducing agent precursors. Such photoreductants are herein referred to as internal hydrogen source photoreductants.  
  A preferred class of internal hydrogen source photoreductants are internal hydrogen source quinones. Quinones incorporating labile hydrogen atoms are more easily photoreduced than quinones which do not incorporate labile hydrogen atoms. Even when quinones lacking labile hydrogen atoms are employed in combination with an external hydrogen source while incorporated hydrogen source quinones are similarly employed without external hydrogen source compounds, the internal hydrogen source quinones continue to exhibit greater ease of photoreduction. When internal hydrogen source quinones are employed with external hydrogen source compounds, their ease of photoreduction can generally be further improved, although the improvement is greater for those internal hydrogen source quinones which are less effective when employed without an external hydrogen source compound.  
  Using quinones exhibiting greater ease of photoreduction results in photographic elements which exhibit improved image densities for comparable exposures and which produce comparable image densities with lesser exposure times. Hence, incorporated hydrogen source quinones can be employed to achieve greater photographic speeds and/or image densities.  
  Particularly preferred internal hydrogen source quinones are 5,8-dihydro-I,4-naphthoquinones having at least one hydrogen atom in each of the and 8 ring positions. Other preferred incorporated hydrogen source quinones are those which have a hydrogen atom bonded to a carbon atom to which is also bonded the oxygen atom of an oxy substituent or a nitrogen atom of an amine substituent with the further provision that the carbon to hydrogen bond is the third or fourth bond removed from at least one quinone carbonyl double bond. As employed herein the term amine substituent&#34; is inclusive of amide and imine substituents. Disubstituted amino substituents are preferred. l,4- Benzoquinones and naphthoquinones having one or more I or 2&#39;-hydroxyalkyl, alkoxy (including alkoxyalkoxy--particularly l or 2&#39;-alkoxyalkoxy, hydroxyalkoxy, etc), 1&#39; or 2&#39;-alkoxyalkyl, aralkoxy, 1&#39; or 2&#39;-acyloxyalkyl, 1 or 2&#39;-aryloxyalkyl, aryloxyalkoxy, I or 2&#39;-aminoalkyl (preferably a l&#39; or 2&#39;-aminoalkyl in which the amino group contains two substituents, at least one of which is an electronegative or aryl substituent, l or 2&#39;-aroyloxyalkyl, alkylarylamino, dialkylamino, N,N-bis-(l-cyanoalkyl)amino, N-aryl-N-(lcyanoaIkyIIamino. N-alkyI-N-(l-cyanoalkyllamino, N,N-bis( I-carbalkoxyalkyUamino, N-aryI-N-( I- carbalkoxyalkyhamino, N-alkyl-N-( l-carbalkoxyalkyl )amino, N,N-bis(l-nitroalkyl)-amino, N-alkyl-N-( lnitroalkyl )amino, N-aryl-N-( l-nitroalkyl)amino, N,N-bis-l -acylalkyl)amino, N-alkyl-N-( I- acylalkylJamino, N-aryl-N-( l-acylalkyUamino, pyrrolino. pyrrolidino, piperidino, and/or morpholino substituents in the 2 and/or 3 position are particularly preferred. Other substituents can, of course, be present. Unsubstituted 5,8-dihydro-l,4-naphthoquinone and 5,8-dihydro-I,4-naphthoquinones substituted at least in the 2 and/or 3 position with one or more of the abovelisted preferred quinone substituents also constitute preferred internal hydrogen source quinones. It is recognized that additional fused rings can be present within the incorporated hydrogen source quinones. For example, l,4-dihydro-anthraquinones represent a use&#39; ful species of 5.8-dihydro-l,4-naphthoquinones useful as incorporated hydrogen source quinones. The aryl substituents and substituent moieties of incorporated hydrogen source quinones are preferably phenyl or phenylene while the aliphatic hydrocarbon substituents and substituent moieties preferably incorporate twenty or fewer carbon atoms and, most preferably, six or fewer carbon atoms. Exemplary preferred internal hydrogen source quinones are set forth in Table V.  
 TABLE V Exemplary lntcmal Hydrogen Source Quinones PR-7o 5,8-dihydrol ,4-naphthoquinone PR-77 5,B-dihydroQ,6,7-trimethyl- I ,4-  
 naphthoquinone PR-78 5.8-dihydro-fi,7-dimethyl-2-phenyl- 1,4-naphthoquinone PR-79 5,8-dihydro-2.S.8-trimethyll .4-  
 naphthoquinonc PR-8O 2 5-bis( dimethylamino I ,4-benzoquinone PR-B I 2,S-dimethyl-B,6-bis(dimcthylamino l ,4-  
 benzoquinone PR-82 2 5dimethyl-3 ,(v-bispyrrolidinol ,4-  
 benzoquinonc PR-83 Z-ethoxy-S-methyll ,4-benzoquinone PR-84 2,6-dimethoxyl ,4-benzoquinone PR-SS 2,5-dimethoxyl ,4-hcnzoquinone PR-86 2,6-diethoxy-l ,4-benzoquinonc PR-87 2,5-dielhoxy-l ,4 bcnzoquinone PR 88 2,5-bisf Q-methoxyethoxy l ,4-benzoquinone PR-S&#39;) 2.S-bist/i-phcnoxyethoxy I ,4-  
 benzoquinone PR-9O 2,5-diphenethoxyl ,4-benzoquinone PR-92 2,S-di-isopropoxyl ,4-ben2oquinone PR-93 2,5-di-n-butoxyl ,4-henzoquinone PR94 2,5-di-sec-butoxyl ,4-bcnzoquinone PR-95 2-( N-ethylacetamidomcthyl |-5tertbutyl l Abenzoquinonc PR-9fi bis[ 2-( S-mcthyl- I .4bcnzoquinone-2yl) ethyl lether PR 2-mcthylS-mttrpholinomethyll .4-  
  henzoquinone PR-JS 2,3.5-trimethyl6-morpholinomethyl-l ,4  
 benmquinone PR-JQ Zj-bisImorpholinomethyl )-I ,4-benzoquinone PR-IUO 2-( l hydroxy 2methyl-n-propyl)- S-methyll ,d-bcnzoquinone PR- l ()I 2hydroxymcthyl3,5,6-trimethyl-I ,4-  
 henzoquinonc PR- I02 2-( I-hydroxycthyl )-5-mcthyll .4-  
 henzoquinonc PR- I05 24 l,l-dimethyl2-hydroxyethyl) -5-methyl- I ,d-bcnzoquinone PR- I06 2-( l-acetnxycthylI-S-methyll ,4-  
 benzoquinone PR I 08 2-( Lethoxyethyl)-5-methyl l ,4-  
 benmquinonc PR- I09 2-( l-isopropoxyethyl)-5-methyll .4-  
 benzoquinonc PR-l IO 2-chloroS-n-uctylaminol ,4- naphthoquinonc PR-l l l I .4-dihydrol ,4-dimethylanthraquinone PR-| I2 I .4-dihydro-2,3-dimcthylanthraquinone PR-l I3 2-dimethylamino-I ,4-naphthoquinonc PR-l I4 Z-methoxy- I .4-naphthoquinone PR-I l5 Z-benryloxy-l 4naphthoquinone PR-I l6 2-methoxy3chloro- I ,4-naphthoquinone PR-I I7 2,3-dimethoxy-I .4-naphthoquinone PR-I I8 2,3-dicthoxy- I .4-naphthoquinone FRI 19 Z-ethoxyl ,4-naphthuquinone PR- I 20 lphenethuxy-l ,4-naphthoquinonc PR- 1 2 I 2-( Z-methoxyethoxy I .4-naphthoquinonc PR I 22 2-( Z-ethoxycthoxy I ,dmaphthoquinone Prl 23 2-( Z-phenoxy lethuxy- I ,4-naphthoquinonc PR- I 24 2-cthoxy-5-methoxyl .4-naphthoquinone PR- I 25 Z-ethoxyb-mcthoxy- I 4naphthoquinonc PR- l 26 Z-ethoxyJ-methoxyl A-naphthoquinone PR- l 27 Z-n-propoxyl ,4naphth0quinonc PR- l 28 2-[ hydrmtypropoxy l- I ,4-naphthoquinone PR- 29 lisupropoxyl ,4maphthoquinone PR- l 30 lmethoxy-2-isopropoxy-I 4naphthoquinone PR- I 3] 2-n-butoxy- I ,4-naphthoquinonc PR- l 32 lscc-butuxy- I ,4-naphthoquinone PR- [33 Z-n-pentoxy-l .4 naphthoquinonc PR- I 34 2 n-hexoxy l .4-naphthoquinorle PR- I 35 Z-n-heptoxy- I 4-naphthoquinone PR- l 36 I-acetoxymethyl-3-methyl-l .4-naphtho- TABLE v fontinued Exemplary lntcrnnl Hydrogen Source Quinorics -naphthoquinonc PR- I 46 e-hromwi-iso &#39;iropoitvl .4-n4tphtlioquinonc PR- l 47 Z-clhoxy d-mcthyh l ,4-tiaphtltoc uinone PR- l 4 8 Z-chlitrol plpcridinol ,-l-n uphthoq uinone PR l 4) Z-llll ii pholinol ,4-niiplilh0tiUllllll&#39;lk PR l 50 lidipipcridino-l ,4&#39;naplitlioqumonc To form a radiation-sensitive composition useful in the present invention it is merely necessary to bring together the photorcductant and the triazoliuin salt in the presence of labile hydrogen atoms. The radiation sensitive composition can then be brought into a spacially fixed relationship, as by coating the composition onto a support to form a photographic element according to the present invention. For maximum efficiency of performance t is preferred that the components of the radiationsensitivc composition, particularly, the photoreductunt. the triazoliuni salt and the external hydrogen source. it any, be intimately associated. This can be readily achieved. for example, by dissolving the reactants in a solvent system,  
  The solvent system can be a common solvent or a combination of miscible solvents which together bring all of the reactants into solution. Typical preferred solvents which can he used alone or in combination are lower alkanols. such as methanol, ethanol, isopropanol, t-butanol and the like; ketones, such as methylethyl kc tone, acetone and the like, water, liquid hydrocarbons; chlorinated hydrocarbons, such as chloroform, ethyl enc chloride, carbon tetrachloride and the like; ethers, such as diethyl ether, tetrahydrofuran, and the like; acetonitrile; dimethyl sulfoxide and dimethyl formamide.  
  For ease of coating and for the purposes of imparting strength and resilience to the radiation-sensitive layer it is generally preferred to disperse the radiationsensitive reactants in a resinous polymer matrix or binder. A wide variety of polymers can be used as binders. In order to he useful it is only necessary that the binders be chemically compatible with the radiationsensitive reactants. in addition to performing their function a hinder the polymers can also serve as external hydrogen sources to supplemenl or replace other hydrogen sources as described above, For example, any of the polymers set forth in Table vil can be used both as binders and as external hydrogen sources.  
  It is preferred to employ linear filrnlorming polymers such as, for example, cellulose compounds, such as ethyl cellulose, bntyl cellulose. cellulose. acetate, cellulose triacetate, cellulose butyrate. cellulose acetate butyrate and the like; vinyl polymers, such as poly( vinyl acetate), poiytvinylidene chloride), at polyivinyl acetall such as polyt vinyl hutyral), polyivinyl chloridcwo vinyl acetate), polystyrene, and polymers of alkyl acrylates and methacrylatcs including copolyrners incorporating acrylic or methacrvlic acid, and polyesters, such 14 as polytethylcne glycolwo isophthalic acid-coterephthalic acid), polytptyclohcxanc t&#39;licarhoxylic acid-co-isophthalic acid-cocyclohexylcnebismcthanoll polyp CyClUhCXllnCLllLIUl&#39; liivllL acnhco-LZAA- tetramethylcyclobutaiic-l,l-diol) and the like. The condensation product of cpichlorohydrin and bispheno] is also a p eferred useful binder. Generally any binder known to have utility in photographic elements and, particularly, diazo photographic elements can be used in the practice of this invention. These binders are well known to those skilled in the art so that no useful purpose would be served by including an extensive cat aloguc of representative binders in this specification. Any of the \ehicles disclosed in Product Lice-trim; [mica Vol. 92, Dec, i9 1, publication 9232. at page 108, can be used as binders in the photographic elements of this invention.  
  While the proportions of the reactants forming the radiation sensitive layer of a photographic element can be varied widely. it is generally preferred for most effi cient utiliyation oi the reactants that they be present in roughly stoichioinetric conccntrationsthat is, equal molar concentrations. One or more of the reactants can, of course, be present in excess. For example, where the external hydrogen source is also used as a binder. it is typically present in a much greater concentration than is essential merely for donation of labile hydrogen atoms. lt is generally preferred to incorporate from il.l to ill moles ofthe triazolium salt per mole of the photorcductant. External hydrogen sources supplied solely to perform this function are typically con veniently incorporated in concentrations of from 0.5 to 10 moles per mole of photoreductant. Where a metal is added for the purpose of chelating the azo-amine dye, it is preferably incorporated in a proportion of from 0.1 to 10 moles per mole of triazolium salt. The binder can account for up to 99% by weight of the radiatioiisensitive layer, but is typically employed in proportions of from 5!) to 90? by weight of the radia tion-sensitivc layer it is. of course, recogni/ed that the binder can be omitted entirely from the radiation sensitive layer. The surface r areal densities of the reactants can vary as a function of the azoamine dyes formed and the image densities desired it is generally preferred to incorporate the triazolium salt in a con centration of at least l X l!) moles per square decime ter and, most preferably, in a concentration of from l X l0 to l X It)&#34; moles per square decimeter The areal densities of the remaining reactants are, of course, proportionate. Typically the fllLlldlIOIrSfiflSlUVfi layer can vary widely in thickness depending on the characteristics desired for the photographic clement cg image density, flexibility, transparency, etc. For most photographic applications coating hicknesses in the range of from 1&#39; microns to 20 microns are preferred.  
  Any conventional photographic support can he used in the practice of this invention. Typical supports in clude transparent supports, such film supports and glass supports as well :is opaque supports, such as metal and photographic paper supports. The support can be either rigid or flexible. Preferred photographic sup ports for most applications are paper or film supports. The support can incorporate one or more subbing layers for the purpose of altering its surface properties. Typically subbing layers are employed to enhance the adherency of the radiation-sensitive coating to the sup port. Suitable exemplary supports are disclosed in Product Licensing Index Vol. 92, December I97 I, publication 9232, at page I08.  
  The radiation-sensitive layer can be formed on the support using any conventional coating technique. Typically the reactants, the binder (if employed) and any other desired addenda are dissolved in a solvent system and coated onto the support by such means as whirler coating, brushing, doctor blade coating, hopper coating and the like. Thereafter the solvent is evaporated. Other exemplary coating procedures are set forth in the Product Licensing Index publication cited above, at page 109. Coating aids can be incorporated into the coating composition to facilitate coating as disclosed on page I08 of the Product Licensing Index publication. It is also possible to incorporate antistatic layers and/or matting agents as disclosed on this page of the Product Licensing Index publication.  
  It is a distinct advantage of this invention that the photographic elements can be processed in a dry state using commercially available exposure and processing equipment. Exposure to actinic radiation in the ultraviolet or visible portions of the spectrum can be readily achieved using mercury arc lamps, carbon arc lamps, photoflood lamps, lasers and the like. Negative images can be formed by exposure through a positive stencil or transparency while positive images can be formed by exposure through a negative stencil or transparency.  
  To avoid direct printout on exposure with the consequent necessity of fixing where uniform reexposure to actinic radiation is contemplated, the radiation sensitive layer is maintained significantly less basic than is required to convert the reducing agent precursor to the reducing agent. While the exact degree of permissible basicity of the radiation-sensitive layer will vary somewhat as a function of the specific reactants chosen, it is generally preferred to avoid the incorporation of strongly basic reactants in the radiationsensitive layer. For this reason components of the radiation-sensitive layer are chosen to be free of strongly basic moieties. It is preferred, for maximum protection against premature and/or background printout, that the radiation-sensitive layer be maintained neutral or on the acid side of neutrality.  
  The latent image that is produced in the photographic element on exposure is easily developed using gaseous ammonia processors, such as those which release moist ammonia vapors at ambient pressure or those which use high pressure anhydrous ammonia gas. Other volatile bases, such as methyl amine, dimethyl amine, trimethyl amine, ethyl amine, diethyl amine, triethyl amine, propyl amine, butyl amine, etc., can be used. Although wet processing is not preferred, it is also contemplated that the photographic elements of this invention can be developed using aqueous alkaline solutions. It is contemplated that the radiation-sensitive layer or an adjacent layer of the photographic element can contain a base source which is convertible to a base at will. For example, it is contemplated that the radiationsensitive layer can contain a compound that will release ammonia on exposure to heat or other activating energy.  
  This invention is further illustrated by the following examples of preferred embodiments:  
 PREPARATION I Preparation of l-methyl-Z-phenyl-ZH-l,2,3-triazolium tetrafluoroborate (T-l) Reaction of glyoxal with two equivalents of phenylhydrazine hydrochloride in the presence of excess sodium acetate, followed by treatment of the product with hot aqueous cupric sulfate gave 2-phenyl-2H- l,2,3-triazole. This material was reacted with methyl fluorosulfonate to give l-methyl-Z-phenyl-ZH-l,2,3- triazolium fluorosulfonate, which when treated in aqueous solution with sodium tetrafluoroborate gave T-l as colorless plateletts, m.p. 137.5 to l39.5C.  
 PREPARATION II Preparation of l-methyI-2-phenyl-5(or6)-nitro-2H- l,2,3-benzotriazolium hexafluorophosphate (T-6) 2,4-dinitrochlorobenzene was reacted with phenylhydrazine in refluxing ethanol to give 5-nitro-2-phenyl- 2H-l,2,3-triazole. THis compound was then treated with methyl fluorosulfonate followed by aqueous potassium hexafluorophosphate to give T-6 as a colorless powder, mp 235C.  
 PREPARATION III Preparation of l.2-diphenyl-2H-l,2,3-naphtho {1,2-d] triazolium tetrafluoroborate IT&#39;S) Diazotized aniline was reacted with one equivalent of N-phenyl-Zmaphthylamine in aqueous ethanol to give Z-phenyIaminolphenylazonaphthalene which when oxidized with N-bromosuccinimide in ethyl acetate solution gave T-8 as off-white needles, mp 277.0 to 278.0C.  
 PREPARATIONS IV, V and VI PREPARATIONS VIII XII Preprations of Triazolium Salts T-26, T-28, T-29, T-30 and T-3 l Compounds T-26, T-ZS, T-29, T-30, and T-3l were also prepared by following the procedure outlined in Preparation VII.  
 EXAMPLES l THROUGH 12 In each instance a radiation-sensitive coating composition was prepared as set forth in Table VI incorporating one of the triazolium salts, the preparation of which is described above.  
 TABLE VI Radiation-Sensitive Coating Composition Cellulose acetate butyrate 0.66 g.  
 TABLE Vl-Continued Radiation-Sensitive Coating Composition Lldichloroethane ll.3 g. Methanol L98 g. Z-isopropoxy-l .4-naphthoquinone (PR-129) L millimolcs Triazolium Salt 10.00 millimoles Each coating composition was coated at a wet thickness of 100 microns on 100 micron poly(tetrafluoroethylene) film base. After the solvents had evaporated, a portion of the coating was exposed to ultraviolet light through a black and white transparency and then the coating was treated with ammonia fumes. In each case a negative of the original transparency was obtained. Table Vll lists the image colors and backgrounds obtained with the various triazolium salts.  
 TABLE Vll Exemplary Photographic Elements TABLE Vlll Exemplary Dye Stabilities Ex. Dye Forming Half-life of Image No. Salt Photoreductant (days) l3 T-8 PR-l29 40 t4 T-l7 PR-l29 3O T-l7 PR-l02 90 I6 T-l8 PR-l02 65 10 11 T-2l PR-l29 18 T PR-l02 95 t9 T-26 PR-l02 45 20 T-28 PR-IOZ l85 2| T-BO PR&#39;lOZ EXAMPLES 22 THROUGH 28 The procedure of Examples 1 through 12 was followed, except that radiation-sensitive coatings were 20 formed 150 microns in thickness, the radiationsensitive coating composition was as set forth in Table IX.  
 TABLE IX 25 Radiation-Sensitive Coating Composition Cellulose acetate butyrate L00 gram l.2-Dichloroethane 9.0 ml Methanol 2.5 ml N.N-Dimethylformamidc 4.0 ml Photoreductant 1.00 millimole 30 Triazolium Salt 1.00 millimole HS-2 (Example 24 only) 1.00 millimole Table X lists the image colors and backgrounds obtained with various triazolium salts and photoreductants.  
 TABLE X EXAMPLES 13 THROUGH 21 The photographic elements prepared in Examples 3 through l0 and similar photographic elements differing by the incorporation of 2-(l-hydroxyethyl)-S-methyl- 1,4-benzoquinone (PR-l02) as a photoreductant were evaluated for dye fading characteristics.  
  The photographic elements were all identically subjected to contact exposure for 8 seconds on an exposure unit commercially available under the trademark lBM Microcopier ll. This was followed by development with anhydrous ammonia at 75 psi. At this point the green image densities were measured. Also the blue densities of the backgrounds were measured. The developed photographic elements were placed on a desk top in a room lighted by two banks of three GE F4OOW Cool White fluorescent lights six and eight feet from the desk surface. The half-life reported in Table VIII is the time elapsed in days before the dye had irreversibly faded to destroy one-half of the azo-amine dye initially present. The blue density of the background was measured after two weeks to provide a measure of background yellowing. In Example 13 the blue density had increased 0.02; in Examples 14 and 15 the blue density had increased 0.04 and in Example 16 the blue density had decreased 0.02. This indicated a low level of yellowing below that detectable by casual inspection.  
 Exemplary Photographic Elements Ex. Photorc- Triazolium Exposed No. ductant Salt Areas Unexposed Areas 22 PR-33 T-33 Orange Very light yellow 23 PR-4l T-l7 Pink Very light pink 24 PR-68 T-8 Pale orange Colorless 25 PR-77 T-25 Deep magenta Light magenta 26 PR- I02 T l Pale orange Colorless 27 PR-l03 T-b Pale orange Colorless 28 PR-l l5 T-l8 Neutral Colorless While the images and backgrounds varied in density and hue, in each instance the image was clearly distinguishable from the background by visual inspection. This demonstrated that a variety of photoreductants can be employed in the practice of this invention.  
  The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
 What is claimed is:  
  1. In a photographic element having a support and at least one radiation-sensitive image recording layer, the improvement in which said image recording layer is comprised of a source of labile hydrogen atoms. a triazolium salt capable of reduction to an azo-amine dye, and a photoreductant capable of producing a base activatible reducing agent precursor on exposure to actinic radiation in the presence of said labile hydrogen atoms.  
  2. In a photographic element according to claim 1 the further improvement in which said photographic element incorporates hydrogen source means external of said photoreductant for supplying the labile hydrogen atoms.  
  3. In a photographic element according to claim 2 the further improvement in which said external hydrogen source means incorporates a labile hydrogen atom at tached to a carbon atom which is also bonded to the ox ygen atom of an oxy substituent or the nitrogen atom of an amine substituent.  
  4. In a photographic element according to claim 2 the further improvement in which said external hydrogen source means is a polymer and also serves as a binder for said image recording layer.  
  5. In a photographic element according to claim 4 the further improvement in which said polymer binder is a cellulosic compound.  
  6. In a photographic element according to claim 5 the further improvement in which said polymer binder is cellulose acetate butyrate.  
  7. In a photographic element according to claim 2 the further improvement in which said external hydrogen source means is phenyl-[.Z-ethanediol.  
  8. In a photographic element according to claim 1 the further improvement in which said photoreductant is a diazoanthrone.  
  9. In a photographic element according to claim 8 the further improvement in which said diazoanthrone is a lO-diazoanthrone.  
  10. In a photographic element according to claim 1 the further improvement in which said photoreductant is a beta-ketosulfide.  
  11. In a photographic element according to claim 10 the further improvement in which said photoreductant is a thiochromanone.  
  I2. In a photographic element according to claim I] the further improvement in which said photoreductant is 2(4-tolyl)thiochromanone.  
  13. In a photographic element according to claim 1 the further improvement in which said photoreductant is a quinone, a disulfide, a phenazinium salt, a betaketosulfide. a nitroarene, a diazoanthrone, or a mixture of two or more of these.  
  14. In a photographic element according to claim I the further improvement in which said photoreductant incorporates one or more labile hydrogen atoms capable of converting said photoreductant to a base activatible reducing agent precursor on exposure to actinic radiation.  
  15. In a photographic element according to claim 14 the further improvement in which said photoreductant incorporates a labile hydrogen atom attached to a carbon atom which is also bonded to the oxygen atom of an oxy substituent or the nitrogen atom of an amine substituent.  
  16. In a photographic element according to claim 14 the further improvement in which said photoreductant incorporating one or more labile hydrogen atoms capable of converting said photoreductant to a base activatible reducing agent precursor on exposure to actinic radiation is a quinone with the further provision that said labile hydrogen atom forms a carbon to hydrogen bond which is the third or fourth bond removed from a carbonyl quinone bond.  
  17. In a photographic element according to claim 16 the further improvement in which said quinone pho toreductant is a S.8-dihydro-l ,4naphthoquinone.  
  18. In a photographic element according to claim 16 the further improvement in which said quinone photoreductant incorporates as a hydrogen source a 2 or 3 position I or Z-hydroxyalkyl substituent.  
  19. In a photographic element according to claim 16 the further improvement in which said quinone photoreductant incorporates as a hydrogen source a 2 or 3 position aralkoxy substituent.  
  20. In a photographic element according to claim 19 the further improvement in which said quinone photoreductant incorporates as a hydrogen source a 2 or 3 position benzyloxy substituent.  
  21. In a photographic element according to claim 1 the further improvement in which said triazolium salt contains an aromatic ring fused with its triazole nucleus.  
  22. In a photographic element according to claim 21 the further improvement in which said triazolium salt is a benzotriazolium salt.  
  23. In a photographic element according to claim 21 the further improvement in which said triazolium salt is a naphthotriazolium salt.  
  24. In a photographic element having a support and at least one radiation-sensitive image recording layer, the improvement in which said image recording layer is comprised of a source of labile hydrogen atoms, a photo-reductant capable of producing a base activatible reducing agent precursor on exposure to actinic radiation in the presence of said labile hydrogen atoms, and a triazolium salt capable of reduction to an azo amine dye and of the formula wherein Z is comprised of the atoms necessary to complete a fused, aromatic ring structure; y is l or 2; R is an aromatic or aromatic-like heterocyclic group; R is an aromatic substituent. an aromatic-like heterocyclic substituent or an alkyl group having from I to 20 carbon atoms and X is an anion.  
  25. In a photographic element according to claim 24 the further improvement in which R is a phenyl group.  
  26. In a photographic element according to claim 25 the further improvement in which R&#39; is an alkoxy substituted phenyl group.  
  27. In a photographic element according to claim 24 the further improvement in which R is a lower alkyl group having from I to 6 carbon atoms.  
  28. In a photographic element according to claim 24 the further improvement in which at least one of R and R is an electronegative group.  
  29. In a photographic element according to claim 28 the further improvement in which said electronegative group includes as an electronegative substituent a nitro group.  
  30. In a photographic element according to claim 28 the further improvement in which said electronegative group includes as an electronegative substituent a halogen atom.  
  31. In a photgraphic element according to claim 24 the further improvement in which said triazolium salt is a bistriazolium salt.  
  32. In a photographic element according to claim 31 the further improvement in which R is a phenylene or naphthalene group.  
  33. In a photographic element according to claim 24 the further improvement in which said anion is a nonnucleophilic anion.  
  34. In a photographic element according to claim 33 the further improvement in which said anion is a tetrafluoroborate or hexafluorophosphate anion.  
  35. in a photographic element according to claim 24 the further improvement in which said photoreductant is a quinone.  
  36. In a photographic element according to claim 35 the further improvement in which said quinone is a l,4- benzoquinone.  
  37. In a photographic element according to claim 35 the further improvement in which said photoreductant is a 1,4-naphthoquinone.  
 38. An image recording process comprising converting a photoreductant within a selected areal portion of a radiation-sensitive layer of a photographic element to a reducing agent precursor by imagewise exposing the photoreductant to actinic radiation while in reactive contact with labile hydrogen atoms,  
 activating the precursor with a base to form a reducing agent and reducing triazolium salt present within the selected areal portions containing the reducing agent to azoamine dye.  
  39. An image recording process according to claim 38 comprising utilizing the base in the gaseous phase.  
  40. An image recording process according to claim 38 in which the precursor is activated by ammonia.  
  41. An image recording process according to claim 38 comprising chelating the azoamine dye.  
  42. An image recording process according to claim 38 in which the radiation-sensitive layer of the photographic element is exposed to visible light.  
  43. An image recording process according to claim 38 in which the radiation-sensitive layer of the photographic element is exposed to ultra-violet radiation.  
 44. An image recording process comprising imagewise exposing a radiation-sensitive layer of a photographic element containing a quinone photoreductant, a source of labile hydrogen atoms and a triazolium salt.  
 activating the radiation-struck quinone photoreduc tant with a base and reducing the triazolium salt adjacent the activated radiation-struck quinone photoreductant to azoamine dye.  
  45. An image recording process according to claim 44 in which a binder is provided to act as a source of labile hydrogen atoms and transferring a portion of these labile hydrogen atoms from the binder to the radiation-struck quinone to form a reducing agent precursor.  
  46. An image recording process according to claim 44 in which said quinone incorporates said source of labile hydrogen atoms.