in the past two decades , 
 interest in porphyrins with aromatically 
 extended -systems has been steadily on the rise . today areas of their application encompass optical limiting , organic light - emitting diodes ( oleds ) and other electronic 
 devices , upconversion by sensitized triplet progress in all of these areas depends on the availability 
 of molecules with different functional groups , optimal solubility , 
 and tailored photophysical properties , warranting continuous development 
 and optimization of synthetic methods . among -extended 
 porphyrins , fully symmetrical molecules 
 such as tetrabenzoporphyrins , tetranaphthporphyrins , and tetraanthraporphyrins captured the most attention , in part because 
 their synthetic chemistry has been most thoroughly developed . these chromophores are characterized by strong and narrow absorption 
 bands in the red spectral region and form brightly phosphorescent complexes with pd and pt that are of interest for oled and imaging applications . in contrast , 
 asymmetrically -extended porphyrins , which also have been known 
 for a long time , have been studied only occasionally . structural asymmetry generally causes broadening of the porphyrin 
 optical spectra , which may be seen as a disadvantage from the applications 
 point of view . , for technologies that rely on nonlinear 
 optical properties , asymmetrical -extension may bring about 
 unique possibilities , for example , as a method to increase two - photon 
 absorption ( 2pa ) cross sections . a number of porphyrin - based systems with enhanced 2pa have been 
 designed in the past , and in some cases 2pa cross sections of several 
 thousand gm units have been reported . however , in only a few cases have triplet states of these systems 
 been evaluated in parallel . triplet states , on 
 the other hand , are central to several key applications of porphyrins , 
 including two - photon photodynamic therapy ( 2p pdt ) and two - photon 
 phosphorescence lifetime microscopy ( 2plm ) of oxygen . in those cases when evaluation of the triplet states of 2p - absorbing 
 porphyrins has been attempted , measurements have been performed by 
 indirect methods , such as quantification of singlet oxygen ( a product 
 of the triplet quenching reaction ) or measuring downstream effects 
 of singlet oxygen itself . such methods , 
 however , can be subject to major errors due to a large number of interfering 
 parameters . at the same time , it is quite 
 possible that modifications of porphyrins leading to an increase in 
 2pa can simultaneously cause severe triplet quenching effects , e.g. , 
 via formation of low - lying charge transfer states and/or by influencing 
 the vibrational dynamics of the macrocycle , enhancing its nonradiative 
 triplet decay . as a result , while gaining in 
 2pa , these porphyrins could lose their other critical property , i.e. , 
 the ability to form long - lived triplet states . our goal was 
 to develop 2p - absorbing porphyrins whose triplet states 
 can be monitored directly by emission . the selection rules determining 
 linear one - photon ( 1p ) and 2p transition probabilities in centrosymmetrical 
 molecules , such as regular metalloporphyrins , are mutually exclusive . consequently , strongly allowed 1p transitions 
 into b ( soret ) and q states , which are 
 states of ungerade symmetry , are not allowed for 
 2pa . on the other hand , gerade states , which can 
 be accessed via 2pa , lie at much higher energies , and their 2p spectra overlap with linear transitions ( e.g. , 
 q bands ) , causing the 2p excitation pathway to be overshadowed by 
 1p absorption . the above selection rules , however , should be relaxed 
 if there is no center - of - inversion symmetry in a porphyrin molecule , 
 causing 1p states to become accessible by 2pa . given that pt 
 and pd complexes of -extended porphyrins exhibit 
 strong phosphorescence and that asymmetric -extension significantly 
 affects the electronic structure of porphyrins , we set out to examine whether asymmetrically -extended pt 
 and pd porphyrins can act as efficient triplet chromophores with intrinsically 
 enhanced 2pa . here we present syntheses of nonfully symmetrical -extended syn - dibenzo- and syn - dinaphthoporphyrins 
 ( dbps and dnps , respectively ; chart 1 ) and 
 their phosphorescent pt(ii ) and pd(ii ) complexes . rational approaches 
 to a number of related tetrapyrroles have been explored previously . in particular , there is an example of a 5,15-meso - diaryl dbp , reported by smith et al . , that is very similar to one of our compounds ( porphyrin 20 ) but was obtained via different route , i.e. , from a sulfolenoporphyrin 
 precursor by the diels  alder reaction . the methodology explored 
 in our synthesis is based on the oxidative aromatization method and its 4,7-dihydroisoindole variant , developed by cheprakov and co - workers . preliminary photophysical measurements showed that all of the synthesized 
 pt porphyrins exhibit very bright phosphorescence at ambient temperatures 
 and increased 2pa compared with nonextended porphyrins . the 2pa is 
 especially enhanced in the case of porphyrins bearing alkoxycarbonyl 
 substituents on the fused benzo rings . the developed methods should 
 facilitate the construction of nonfully symmetrical -extended 
 porphyrins for applications requiring enhanced 2pa / triplet action 
 cross sections , such as 2p pdt and 2plm . two adjacent 
 pyrrole rings in each macrocycle are fused with external aromatic 
 fragments through the -carbon atoms , forming syn- ( or adj- ) dibenzo- and dinaphthoporphyrins . 
 if meso - aryl substituents are disregarded , these 
 macrocycles belong to the c2v symmetry group , unlike regular metalloporphyrins , which 
 have d4h - type symmetry 
 and thus possess a center of inversion . previous studies have shown that planar meso - unsubstituted 
 -extended porphyrins are significantly more emissive than their 
 nonplanar meso - tetraarylated analogues . however , meso - unsubstituted porphyrins are prone 
 to aggregation and often pose serious solubility problems . on the 
 other hand , nonplanar distortions in porphyrins are usually caused 
 by steric repulsion between -pyrrolic substituents ( e.g. , fused 
 benzo rings ) and meso - aryl groups . placing only two meso - aryls opposite to each other allows the macrocycle 
 to evade the strain by undergoing in - plane as opposed to out - of - plane 
 deformation and thus preserve planarity . moreover , in syn - dbps and syn - dnps 
 ( chart 1 ) , aromatic rings are appended to pyrroles 
 only on one side  of the molecule , while the dipyrromethene 
 fragment on the opposite side remains strain - free . mono - aryl - substituted dbp 21 lacking a meso - aryl group between the two benzo substituents was also synthesized . 
 to improve the solubility , the meso - aryl substituents 
 in the majority of the synthesized porphyrins were supplemented by meso - dialkoxycarbonyl groups . in all cases , dft ground - state 
 calculations ( b3lyp/6 - 31 g * ) confirmed planar macrocycle structures 
 ( figure s1 in the supporting information ) . the saturated precursor porphyrins for syn - dbps 
 and syn - dnps may be obtained from dipyrromethanes 
 bearing c1 synthons at the 1- and 9-positions and appropriate unsubstituted 
 counterparts ( scheme 1 ) . following the methods 
 developed by lindsey and co - workers , we chose to use bis(n , n - dimethylaminomethyl ) and bis(propyliminomethyl ) derivatives ( chart 2 ) , which have been shown to minimize scrambling 
 in the condensation reaction . route a was selected because of easier 
 accessibility and higher stability of c1-dipyrromethanes derived from 
 unsubstituted pyrrole . generally , 1,9-bis(n , n - dimethylaminomethyl)dipyrromethanes 
 such as 1 ( chart 2 ) are simpler 
 to synthesize , and they lead to excellent results when condensations 
 are carried out in alcohols . for example , 
 in our case 1 was successfully employed in the synthesis 
 of porphyrin 13 in meoh ( see scheme 3 ) . however , in nonpolar solvents ( e.g. , toluene , benzene ) , 
 which appeared to favor syntheses of the majority of our porphyrins 
 ( see below ) , 1,9-bis(propyliminomethyl)dipyrromethane 2 allowed us to achieve significant improvements in the yield . dipyrromethanes 1 and 2 ( chart 2 ) were 
 prepared in 5070% yield from pyrrole and the corresponding 
 aldehydes . cyclohexadieno- ( 3 and 4 ) , cyclohexeno- ( 5 and 6 ) , and tetrahydronaphthaleno - fused ( 7 ) dipyrromethane 
 esters 
 were synthesized in 7090% yield from the respective pyrroles and aldehydes ( or dimethoxymethane ) following the previously developed 
 procedures ( scheme 2 ) . in the case of sterically more hindered 
 structures 5 and 7 , longer times ( up to 72 h ) were required 
 to complete the condensations . generally , using acetic acid as the 
 solvent , as opposed to dichloromethane , was found to speed up the 
 reactions by factors of 2 . the cyclohexadieno- ( 3 and 4 ) and 
 tetrahydronaphthaleno - fused ( 7 ) dipyrromethane esters were unstable 
 at room temperature and degraded rapidly during purification . ( only compounds that were isolated and fully characterized 
 are identified in the text by bold numbers ) . dipyrromethane esters 
 3 , 4 , and 5 were de - esterified and decarboxylated in a one - pot reaction 
 upon treatment with tfa , while benzyl esters 6 and 7 
 were first converted to carboxylic acids by reduction on pearlman s 
 catalyst ( pd(oh)2/c ) and then 
 introduced into the tfa - mediated decarboxylation without isolation . de - esterification / decarboxylation was carried out immediately prior 
 to the porphyrin synthesis , since ,-unsubstituted 
 dipyrromethanes are even more unstable than their ester precursors 
 and degrade rapidly in air , presumably as a result of oxidation and/or 
 oligomerization . dipyrromethane 12 was the least stable in the series , 
 and it had to be handled especially promptly . on the basis of analyses 
 of the crude reaction mixtures , the yields of the dipyrromethanes 
 ( starting with esters 37 ) ranged from 30 to 65% . reagents 
 and conditions : ( a ) p - tsoh , nbu4cl , ch2cl2 , 
 r.t . , 24 h ( 3 ) , 48 h ( 4 ) , 72 h ( 5 ) . ( b ) p - tsoh , acoh , 24 h ( 6 ) , 48 h ( 7 ) . ( c ) h2/pd(oh)2/c , thf , r.t . , 2448 h. 
 ( d ) ( i ) tfa / ch2cl2 1:1 , 20 c , 1 h ; ( ii ) 
 nahco3 . the [ 2 + 2 ] assembly leading 
 to the target porphyrins is shown 
 in scheme 3 . according 
 to the original procedures , condensation of 1,9-bis(n , n - dimethylaminomethyl)- or 1,9-bis(n - propyliminomethyl)dipyrromethanes ( chart 2 ) with 1,9-unsubstituted dipyrromethanes is carried out optimally 
 in refluxing methanol in the presence of a 10-fold molar excess of 
 zn(oac)2 . in cases when the reactants bear functional groups sensitive to 
 solvolysis , methanol may be substituted by toluene , also under reflux , 
 in which case 1,9-bis(n - propyliminomethyl)dipyrromethanes 
 are the substrates of choice . reagents and conditions : ( a ) 
 ( i ) zn(oac)22h2o ( 10 equiv ) , meoh , reflux , 
 2 h ; ( ii ) ddq ( 3 equiv ) , r.t . , 2 h. ( b ) ( i ) zn(oac)22h2o ( 10 equiv ) , c6h6 , ar , reflux , 2 h ; 
 ( ii ) air , reflux , 1218 h. ( c ) ddq ( 3 equiv ) , thf , reflux , 
 3040 min . ( e ) 
 pt insertion : ( method 1 ) pt(acac)2/benzoic acid , 130135 
 c , 26 h ; ( method 2 ) pt(acac)2/phcn , microwave , 
 250 c ( 200 kpa , 105145 w ) , 40 min . pd insertion : 
 pd(ac)2/phcn , microwave , 250 c ( 200 kpa , 
 105145 w ) , 40 min . ( f ) ddq ( 5 equiv ) , toluene , reflux , 10 
 h. ( g ) ddq ( 3 equiv ) , thf , r.t . , 10 min . following 
 the original method , reaction 
 of dipyrromethane 8 with 1 in meoh in the presence of 
 zn(oac)2 gave the zn complex of porphyrin 13 ( zn13 ) 
 in 13% yield . however , applying the same conditions directly to the 
 rest of our substrates proved inefficient . for example , condensation 
 of dipyrromethanes 10 and 2 in meoh gave zn15 in a rather low 8% yield , and when the reaction was attempted 
 in toluene , the yield dropped below 5% . other dipyrromethanes showed 
 similar results . on the basis of uv  vis spectra , we concluded 
 that at least in part the low yields were caused by competing oxidation 
 of dipyrromethanes into dipyrromethenes ( dipyrrins ) , whose formation 
 could be easily detected by characteristic optical absorption . dipyrrins are inert in the condensation . in order to prevent premature oxidation of dipyrromethanes and 
 establish overall milder conditions for the synthesis , the reaction 
 was attempted as a two - step process using dipyrromethane 2 as a reactant . in the first step , dipyrromethanes 912 were 
 condensed with 2 under an inert atmosphere ( ar ) in the 
 presence of zn(oac)2 in refluxing benzene . the latter has 
 a lower boiling point than toluene , helping to avoid side reactions 
 and decomposition of the sensitive dypyrromethanes . the formation 
 of the corresponding dehydroporphyrinogens and depletion of the starting 
 materials was monitored by maldi - tof analysis . once the concentration 
 of the dehydroporphyrinogens stopped changing , usually after 23 
 h , the mixtures were flushed with air and left to react for an additional 
 816 h ( second step ) . at this stage , the reaction progress 
 was monitored by uv  vis spectroscopy , and the refluxing was 
 continued until the ratio of the intensity in the soret band region 
 ( 350400 nm ) to the absorption by the side products 
 ( dipyrrins ) near 500600 nm was at its maximum . it should be 
 noted that not all of the dipyrromethanes were converted into dehydroporphyrinogens 
 in the first step , but the mixtures were simply allowed to reach their 
 respective steady states . subsequent oxidation by air apparently was 
 mild enough to prevent fast oxidation of dipyrromethanes but effective 
 in converting dehydroporphyrinogens into porphyrins . the dipyrromethanes 
 in the meantime continued to undergo condensation to generate new 
 dehydroporphyrinogens for oxidation . these conditions allowed us to 
 obtain cyclohexadieno- ( 14 ) and cyclohexenoporphyrins ( 15 and 16 ) in 2030% yield and the least stable 
 porphyrin 17 in 13% yield . in all cases , aromatization of precursors 1317 into 
 the target dibenzo- 
 ( 1821 ) and dinaphthoporphyrins ( 22 ) requires the removal of either two ( 13 , 14 , 17 ) or four 
 ( 15 , 16 ) hydrogens from each exocyclic ring 
 annealed with the macrocycle , whereas dehydrogenation of less - saturated 
 rings generally occurs much more easily . aromatizations may be inhibited 
 by the formation of porphyrin dications if the basicities of the corresponding 
 free bases are high . the latter is typical 
 of highly nonplanar porphyrins , which must be converted into stable 
 metal complexes ( e.g. , with pd , pt , or cu ) prior to oxidation . planar meso - unsubstituted and 5,15-diarylporphyrins may be oxidized directly as free bases , although metalation usually 
 facilitates the reaction . the transformation 
 of zn17 into zn22 could be observed immediately 
 upon addition of ddq , even at room temperature , by the change of the 
 color of the mixture from red to deep green . similarly , aromatization 
 of porphyrins zn13 and zn14 occurred when they were 
 treated with ddq in thf for just 3040 min , although heating 
 was required . the zn complexes of 18 , 19 , and 22 were isolated in almost quantitative yields . the aromatization of tetraalkoxycarbonylporphyrins 15 and 16 , however , proved to be much more difficult . for example , treatment of 15 as either the free base 
 or the zn complex ( zn15 ) with excess ddq in refluxing 
 thf for 14 h did not show any sign of conversion , while the oxidation 
 in refluxing toluene produced mixtures of aggregated inseparable products . our final targets in this study were phosphorescent pt and pd complexes , 
 and therefore , we turned our attention to the methods developed earlier 
 for the synthesis of similar pt and pd tetraaryltetrabenzo- and tetranaphthoporphyrins . prior to oxidation , zn15 and zn16 were demetalated and then converted into pt and pd complexes 
 ( see below ) . the latter were smoothly oxidized using excess ddq in 
 toluene over 10 h , yielding the desired complexes m20 and m21 ( m = pt , pd ) in 7992% 
 yield . insertion of pt(ii ) into the precursor porphyrins 15 and 16 and the target porphyrins 18 , 19 , and 22 was performed either in benzoic 
 acid 
 melt or using the microwave - assisted 
 method . in the former approach , the free - base 
 porphyrins were heated with a 34-fold molar excess of pt(acac)2 in benzoic acid at 130135 c for 26 
 h. subsequent methanol workup , chromatographic purification , and reprecipitation 
 from ch2cl2/meoh ( 1:50 ) afforded the pt(ii)porphyrin 
 complexes in 2056% yield . in spite of the moderate yields , 
 the benzoic acid method in our hands 
 has proved to be general and frequently leads to success when other 
 methods , such as commonly used refluxing in benzonitrile , fail . however , 
 in this particular instance , the best results were achieved using 
 the microwave - assisted insertion , developed by bruckner and co - workers . microwave treatment of mixtures of the free - base 
 porphyrins and pt(acac)2 ( 34 equiv ) in benzonitrile 
 for 40 min gave the corresponding pt complexes in 92% to quantitative 
 yield . overall , the developed reaction sequences allowed us 
 to prepare 
 the target pt and pd porphyrins in yields of 515% relative 
 to the starting pyrrole esters ( scheme 2 ) . the methods do not require expensive reagents and can be scaled to 
 gram quantities . this section 
 provides a brief 
 overview of the photophysical properties of the newly synthesized 
 porphyrins , while leaving the detailed analysis for a separate account . 
 because of the presence of meso - aryl substituents 
 and alkoxycarbonyl groups , all of the porphyrins were found to be 
 well - soluble in a range of organic solvents ( e.g. , toluene , ch2cl2 , thf , dmf , and dma ) , where they showed no signs 
 of aggregation at the concentrations required for optical measurements 
 and above ( up to 10 m ) . this solvent is especially convenient 
 because of its high boiling point ( 165 c ) , making it possible 
 to deoxygenate solutions by inert gas bubbling ( ar or n2 ) at room temperature without experiencing significant losses in 
 the solution volume . the optical absorption features of the 
 pt and pd complexes of the synthesized porphyrins are very similar 
 to each other , with the bands of the pd porphyrins being red - shifted 
 by 515 nm relative to the pt complexes . the triplet lifetimes 
 of the pd complexes pd19 through pd22 are 810 times longer than those of the respective 
 pt porphyrins , while their phosphorescence quantum yields are 
 about 2 times lower ( table 1 ) . these trends 
 are common for pt and pd porphyrins , and 
 below we discuss only pt complexes pt18 through 
 pt22 , while the properties of the pd complexes 
 can be inferred by analogy . the phosphorescence quantum yields 
 (  ) and lifetimes (  ) were measured at 22 c in deoxygenated 
 solutions . the fluorescence of rhodamine 6 g in etoh ( fl = 0.95 ) was used as a standard . for 
 comparison , under these conditions the fluorescence quantum yield 
 of tetraphenylporphyrin ( h2tpp ) in deoxygenated c6h6 is 0.055 , and the phosphorescence quantum yield of 
 pt meso - tetraphenyltetrabenzoporphyrin ( ph4tbp ) in deoxygenated dmf is 0.085 . the linear absorption and phosphorescence emission 
 spectra of porphyrins 
 pt18 through pt22 are shown 
 in figure 1 , and the relevant data are compiled 
 in table 1 . similar graphs for the pd complexes 
 are shown in figure s2 in the supporting information . it should be noted that the absorption features of zndbps zn18 and zn19 ( figure s3 in the supporting information ) correspond well with 
 the literature data on similar zn complexes . ( a ) 
 absorption and ( b ) phosphorescence spectra of porphyrins pt18 through pt22 in dma . the absorption 
 spectra were normalized by the corresponding q - band maxima ; the inset 
 shows the zoomed q - band region . the phosphorescence spectra were normalized 
 by the respective phosphorescence quantum yields ( table 1 ) . the absorption spectra of all 
 of the synthesized pt porphyrins 
 exhibit well - defined , narrow bands , resembling in that way the spectra 
 of the fully symmetrical pt tetrabenzoporphyrins ( pttbps ) ( d4h symmetry ) . the soret ( or b ) ( s2 ) , q ( s1 ) , and phosphorescence 
 ( t1 ) bands of porphyrins pt18 through 
 pt21 occupy somewhat intermediate positions between 
 the bands of regular nonextended pt porphyrins ( ptps ) and those of pttbps . the q band of pt22 ( max = 
 593 nm ) is bathochromically shifted , approaching the q bands of pttbps 
 ( 605615 nm ) , while its b band is 
 also red - shifted , but broadened similar to the b bands of tetranaphthoporphyrins . these observations can be rationalized , at least 
 to a first approximation , by recalling that q and b bands in regular 
 symmetrical porphyrins are composed of orthogonally polarized transitions 
 ( qx and qy , bx and by ) that are formed by configuration interaction involving single - electron 
 excitations between pairs of nearly degenerate homos and lumos . -extension lifts the degeneracy of one 
 of the homos ( a2u ) , leading to a spectral red shift as 
 well to an increase in the oscillator strength of the q band . just as in fully symmetrical pttbps , the orthogonal transition dipoles 
 in pt syn - dbps and pt syn - dnps are 
 identical to each other . consequently , the x and y bands are fully superimposed , giving rise to narrow spectral 
 lines , similar to those of pttbps . in contrast , in anti - dbps , the x and y dipoles are 
 not equivalent , resulting in multiple spectral lines in both the q- 
 and b - band regions . the transitions 
 in pt18 through pt21 are 
 polarized in the directions in which the syn - dbp 
 molecules have diameters larger than those of regular pt porphyrins 
 but smaller than those of pttbps . in syn - dnp pt22 , on the other hand , the macrocycle diameter along the polarization 
 axes is similar to that of pttbps . the energies of the spectral bands 
 generally follow this simple relationship : the  longer  
 the dipole , the lower the energy of the absorption band . of course , 
 for accurate quantitative interpretation of the spectroscopic data , 
 a detailed computational / photophysical study such as that performed 
 recently for zn benzoporphyrins will 
 be required . in the series of synthesized syn - dbps , porphyrins 
 pt20 and pt21 exhibit the 
 most bathochromically shifted q and b bands , while their phosphorescence 
 maxima are the most hypsochromically shifted . with the assumption 
 that the phosphorescent triplet states ( t1 ) in all of these 
 porphyrins are derived from the same electronic configurations as 
 the s1 ( or s2 ) states , the data for pt20 and pt21 appear to be consistent with 
 the expansion of the -conjugation onto the carbonyl groups 
 in the benzo rings in the macrocycles . this expansion further destabilizes 
 one of the homos , causing a red shift in the absorption , but at the 
 same time decreases the exchange energy ( 2j ) because 
 of the increase in the size of the -system , narrowing the s1t1 gap and 
 raising the energy of the t1 state . between these two porphyrins , 
 pt20 exhibits more bathochromically shifted bands 
 than pt21 , which is consistent with the presence 
 of only one meso - aryl substituent in the latter . the meso - aryl groups in 5,15-diarylporphyrins ( see 
 the x - ray structure in figure 2 and the computed 
 structures in figure s1 in the supporting information ) are almost perpendicular to the porphyrin plane , and yet they participate in the conjugation with the macrocycle , 
 thereby inducing small red shifts in the absorption spectra . ( top ) ortep view of the x - ray crystallographic structure 
 of porphyrin 
 pt19 ( 50% thermal ellipsoids ) with two stacked 
 nonidentical porphyrin molecules in the cell . ( bottom ) view of the plain porphyrin 
 skeleton of pt19 , showing the small nonplanar 
 distortion of the macrocycle and tilts of the two meso - aryl substituents . the aryl group between the two benzo rings is 
 rotated by 83 relative to the porphyrin mean - square plane . the phosphorescence quantum yields 
 of pt syn - dbps 
 ( ph  0.35 ) were found to be among the highest 
 reported to date for phosphorescent tetrapyrroles . the quantum yields 
 were measured against the fluorescence of rhodamine 6 g in etoh ( fl = 0.95 ) , and the emission spectra 
 were corrected for the wavelength dependences of the detector , excitation 
 source , and monochromators . it should be noted that under the same 
 conditions the phosphorescence quantum yield of pt meso - tetraphenyltetrabenzoporphyrin ( ph4tbp ) in deoxygenated 
 dmf was determined to be 0.085 , which is substantially lower than 
 reported previously . the high emission yields of pt syn - dbps are in line with their relatively planar structures 
 ( figure 2 and figure s1 in the supporting information ) , in accordance with the 
 previously observed correlation between nonplanarity of -extended 
 porphyrins and enhanced nonradiative triplet decay . on average only 60% of the triplet state in pt18 through pt21 decays via the nonradiative 
 channel ( table s1 in the supporting information ) , while in , e.g. , highly nonplanar ptph4tbps this fraction 
 is larger than 90% . in dnp pt22 , the proportion 
 of the t1  s0 intersystem crossing is 
 also increased to 90% because of the narrower t1s0 gap . in order to estimate the performance 
 of porphyrins pt18 through pt22 under 2p excitation , 
 we compared their phosphorescence outputs to that of a regular symmetrical 
 pt porphyrin , i.e. , pt tetracyclohexenoporphyrin ( pttchp ) , which possesses d4h symmetry ( figure s4 in the supporting 
 information ) . the phosphorescence quantum yield of pttchp in 
 deoxygenated dma at 22 c is 0.42 . our setup allows time - resolved 
 acquisition of phosphorescence upon excitation by trains of femtosecond 
 pulses from a tunable ti : sapphire laser ( see the supporting information for details ) . in pt porphyrins , because 
 of the ultrafast s1  t1 intersystem 
 crossing and therefore nearly quantitative formation of the triplet 
 state , the corrected 
 integrated intensity of the phosphorescence ( normalized by the phosphorescence 
 quantum yield and plotted against the excitation wavelength ) is directly 
 suitable for comparisons of 2pa cross sections of different porphyrins . 
 to ensure the 2p excitation regime , the signal in all cases was confirmed 
 to exhibit a strictly quadratic power dependence ( slope of the log the results are summarized in figure 3 ( for the numerical data , see table s2 in the supporting information ) . relative 2pa cross sections 
 ( integrated intensities of 2p - excited 
 phosphorescence normalized by the phosphorescence quantum yield ) of 
 pttchp ( d4h ) and the 
 synthesized pt porphyrins . the data are scaled in such a way that 
 the relative 2pa cross section of the most absorbing porphyrin , pt21 , equals 1.0 at 770 nm . it can be seen that the apparent 2pa cross sections of pt syn - dbps and syn - dnps are indeed larger 
 than that of the reference pttchp . in the case of pt22 , measurements could not be conducted at wavelengths shorter 
 that 860 nm because of the interfering linear excitation into the 
 triplet state ( s0  t1 ) by the femtosecond 
 pulses . ( it should be kept in mind that in pt porphyrins , because 
 of the very strong spin  orbit coupling , spin - forbidden s0 the most striking enhancement occurs in 
 the case of porphyrins pt20 and pt21 in which the benzo rings contain alkoxycarbonyl groups , 
 as their apparent 2pa cross sections near 770 nm are 25-fold 
 larger than that of pttchp ( table s2 in the supporting 
 information ) . however , it is also clear that in all of the 
 porphyrins the 2pa continues to rise past 800810 nm , i.e. , 
 twice the maximum of the soret band . apparently , breaking the center - of - inversion 
 symmetry is not the dominant factor in the enhancement of the 2pa , 
 and the most strongly absorbing 2pa states in these porphyrins are 
 still not the same as their linear 1p states . these preliminary 
 findings raise the following questions : what 
 are the 2p - absorbing states in -extended pt porphyrins , and 
 why do alkoxycarbonyl groups cause such a pronounced enhancement of 
 the 2pa ? one obvious notion is that the alkoxycarbonyl groups in porphyrins 
 pt20 and pt21 significantly 
 polarize these molecules . for example , on the basis of dft calculations 
 ( b3lyp/6 - 31 g * ) , the ground - state dipole moment of a zn porphyrin analogous 
 to zn20 is 6.12 d , whereas for the analogue of 
 zn19 it is only 0.85 d ( figure s1 in the supporting information ) . such polarization could 
 in principle lead to an enhancement of 2pa , assuming that in the excited 
 state the dipole moment increases ( or changes sign ) . these and other pertinent photophysical questions should 
 be addressed in a separate study , for which the present work sets 
 the necessary synthetic stage . we have developed a synthesis of pt and pd complexes 
 of nonfully 
 symmetrical syn - dbps and syn - dnps 
 with solubilizing substituents . these macrocycles possess nearly planar 
 structures and phosphoresce in solutions at ambient temperatures with 
 exceptionally high quantum yields . preliminary evaluation showed that 
 structural asymmetry causes an increase in the 2pa into 1p - allowed 
 states ; however , much stronger 2p - absorbing states are positioned 
 at higher energies . descriptions of materials , equipment , and general protocols are 
 provided in the supporting information . hrms data are reported for the highest - intensity peak in the isotope 
 mass distribution and compared to the corresponding peak in the distribution 
 simulated by the mass spectrometer software . the abbreviations used 
 in the h nmr peak assignments are shown on p s20 in the supporting information . 4-methoxycarbonylbenzaldehyde ( 2.40 g , 15 
 mmol ) and pyrrole ( 100 g , 1.5 mol ) were mixed together and purged 
 with ar for 10 min . incl3 ( 0.3315 g , 1.5 mmol ) was added , 
 and the reaction mixture was stirred under ar at room temperature 
 for 1.5 h. naoh ( 1.8 g , 43.5 mmol ) was added to the mixture , and stirring 
 was continued for additional 45 min . the precipitates were removed 
 by filtration , and pyrrole was removed by distillation in vacuum ( 1 
 mmhg , 1820 c ) ; the remaining traces of pyrrole were 
 removed by washing the residue with hexane ( 3  30 ml ) . 5-(4-methoxycarbonylphenyl)dipyrromethane 
 ( 1a ) precipitated from solution as pale - yellow crystals 
 upon cooling of the mixture to 0 c . h nmr ( dmso - d6 )  ( ppm ) : 2.07 ( 12h , s , nch3 ) , 3.26 ( 4h , d , j = 2.51 
 hz , chn(ch3)2 ) , 3.81 
 ( 3h , s , och3 ) , 5.37 ( 1h , s , ch ) , 5.53 ( 1h , d , j = 
 2.8 hz , pyr ) , 5.54 ( 1h , d , j = 2.8 hz , 
 pyr ) , 5.72 ( 1h , d , j = 2.8 hz , pyr ) , 
 5.73 ( 1h , d , j = 2.8 hz , pyr ) , 7.23 ( 2h , 
 d , j = 8.3 hz , ar ) , 7.85 ( 2h , d , j = 8.3 hz , ar ) , 10.51 ( 2h , s , nh ) . to a solution of 1a ( 0.9468 g , 2.9 
 mmol ) in ch2cl2 ( 50 ml ) , n , n - dimethylethyleneiminium iodide ( eschenmoser s salt ) 
 ( 1.3871 g , 6.4 mmol ) was added . the reaction mixture was stirred for 
 1 h at room temperature and then diluted with ch2cl2 ( 350 ml ) , and k2co3 ( 10% aq . , 3  350 ml ) , dried over na2so4 , and concentrated in vacuum . the title compound was 
 precipitated from ch2cl2 upon addition of hexanes , 
 collected by filtration , and dried in vacuum . h nmr ( dmso - d6 )  ( ppm ) : 2.07 ( 12h , 
 s , nch3 ) , 3.26 ( 4h , d , j = 2.51 hz , chn(ch3)2 ) , 3.81 ( 3h , s , och3 ) , 5.37 ( 1h , s , ch ) , 5.53 
 ( 1h , d , j = 2.8 hz , pyr ) , 5.54 ( 1h , d , j = 2.8 hz , pyr ) , 5.72 ( 1h , d , j = 2.8 hz , pyr ) , 5.73 ( 1h , d , j = 2.8 hz , pyr ) , 7.23 ( 2h , d , j = 8.3 hz , ar ) , 7.85 ( 2h , d , j = 8.3 
 hz , ar ) , 10.51 ( 2h , s , nh ) . c nmr ( cdcl3 )  ( ppm ) : 44.2 , 44.9 , 52.0 , 56.6 , 107.1 , 
 107.5 , 107.6 , 128.4 , 128.6 , 128.9 , 129.0 , 129.8 , 131.70 , 131.74 , 147.65 , 
 147.67 , 167.0 . hrms ( esi - tof ) m / z : [ m + h ] calcd for c23h31n4o2 395.24413 , found 395.24368 . 3,5-dibutoxycarbonylbenzaldehyde ( 3.06 g , 
 10 mmol ) and pyrrole ( 66 g , 1.0 mol ) were mixed together and purged 
 with ar for 10 min . incl3 ( 0.221 g , 1.0 mmol ) was added , 
 and the reaction mixture was stirred at room temperature under ar 
 for 1.5 h. naoh ( 1.2 g , 30 mmol ) was added to the mixture , and the 
 stirring was continued for 45 min . the precipitates were removed by 
 filtration , and pyrrole was removed by distillation in vacuum ( 1 
 mmhg , 1820 c ) . the residue was purified by chromatography 
 on a short silica gel column ( 10 cm , ch2cl2 ) 
 to give crude 5-(3,5-dibutoxycarbonylphenyl)dipyrromethane ( 2a ) ( 3.6 g ) . to a solution of 2a ( 3.6 g , 
 8.5 mmol ) in dry dmf ( 10 ml ) was added pocl3 ( 2.74 g , 17.9 
 mmol ) dropwise at 0 c under ar . the reaction mixture was stirred 
 for 1 h at room temperature , poured into a saturated aqueous solution 
 of sodium acetate ( 250 ml ) , extracted with ch2cl2 ( 3  100 ml ) , and dried over na2so4 . the solvent was removed in vacuum , and the residue was purified by 
 column chromatography ( silica gel , ch2cl2/etoac 
 = 4:1 ) to give crude 1,9-diformyl-5-(3,5-dibutoxycarbonylphenyl)dipyrromethane 
 ( 2b ) ( 3.3 g ) . n - propylamine ( 15 
 ml , 183 mmol ) was added to 2b ( 3.3 g , 6.9 mmol ) , and 
 the mixture was stirred for 1 h 
 at room temperature . excess n - propylamine was removed 
 in vacuum to give the title compound 2 as a dark - orange 
 solid ( mp 112114 c ) . h nmr ( cdcl3 )  ( ppm ) : 0.90 ( 6h , t , j = 7.4 hz , ch3 ) , 0.95 ( 6h , t , j = 7.4 hz , ch3 ) , 1.381.49 ( 4h , m , ch2 ) , 1.601.78 ( 8h , m , ch2 ) , 3.41 ( 4h , dd , j1 = 6.8 , j2 = 6.9 hz , nch2 ) , 
 4.30 ( 4h , t , j = 6.7 hz , och2 ) , 5.59 ( 1h , s , broad , ch ) , 5.96 ( 2h , d , j = 
 3.6 hz , pyr ) , 6.50 ( 2h , d , j = 3.6 hz , 
 pyr ) , 7.72 ( 2h , s , nh ) , 8.08 ( 2h , 
 d , j = 1.4 hz , ar ) , 8.55 ( 1h , t , j = 1.4 hz , ar ) . c nmr ( cdcl3 )  ( ppm ) : 11.7 , 13.7 , 19.2 , 24.2 , 30.6 , 44.1 , 62.3 , 
 65.2 , 109.6 , 114.8 , 114.9 , 129.4 , 130.4 , 131.2 , 133.6 , 135.6 , 135.7 , 
 142.2 , 151.4 , 165.7 . maldi - tof ( m / z ) : calcd for c33h44n4o4 560.34 , found 561.24 [ m + h ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c33h45n4o4 561.34349 , found 
 561.34371 . p - toluenesulfonic acid ( 0.090 g , 0.48 mmol ) and tert - butylammonium chloride ( 0.135 g , 0.48 mmol ) were added to a solution 
 of 1-tert - butoxycarbonyl-5,6-dibutoxycarbonyl-4,5,6,7-dihydro-2h - isoindole ( 2 g , 4.75 mmol ) 
 and 3,5-dibutoxycarbonylbenzaldehyde ( 0.727 
 g , 2.4 mmol ) in ch2cl2 ( 50 ml ) . the reaction 
 mixture was stirred at room temperature under ar for 72 h. small amounts 
 of p - toluenesulfonic acid ( 0.045 g , 0.24 mmol ) and tert - butylammonium chloride ( 0.07 g , 0.25 mmol ) were added 
 to the reaction mixture after 24 h and then again after 48 h. the 
 reaction progress was monitored by tlc until the spot corresponding 
 to aldehyde disappeared . the mixture was diluted with ch2cl2 ( 100 ml ) , washed with nahco3 ( 10% aq . , 
 50 ml ) and brine ( 50 ml ) , and dried over na2so4 . the solvent was removed in vacuum , and the residue was purified 
 by column chromatography ( silica gel , ch2cl2/thf = 50:1 ) to give the title compound 5 as an orange 
 oil . h nmr ( cdcl3 )  
 ( ppm ) ( mixture of conformers ) : 0.830.91 ( 12h , m , ch3 ) , 0.95 ( 6h , t , j = 7.3 hz , ch3 ) , 1.221.50 
 ( 16h , m , ch2 ) , 1.501.53 
 ( 18h , m , tbu ) , 1.481.60 ( 4h , m , ch2 ) , 1.681.78 ( 4h , m , ch2 ) , 2.242.47 ( 2h , m , chh ) , 2.552.80 ( 2h , m , chh ) , 2.993.27 ( 8h , m , chh , 
 ch ) , 3.924.10 ( 8h , m , och2 ) , 4.30 ( 4h , t , j = 6.6 hz , och2 ) , 
 5.505.54 ( 1h , m , broad , ch ) , 
 7.887.95 ( 2h , m , ar ) , 8.398.44 ( 1h , m , ar ) , 8.528.50 
 ( 2h , m , nh ) . c nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 13.62 , 13.64 , 13.71 , 
 19.01 , 19.04 , 19.1 , 19.2 , 22.2 , 22.3 , 22.4 , 22.5 , 23.5 , 23.6 , 23.7 , 
 23.8 , 28.39 , 28.42 , 30.3 , 30.47 , 30.52 , 30.54 , 30.6 , 40.56 , 40.58 , 
 40.7 , 40.8 , 40.90 , 40.94 , 40.96 , 41.00 , 41.1 , 64.45 , 64.49 , 64.55 , 
 64.60 , 64.63 , 65.3 , 80.63 , 80.65 , 80.69 , 116.9 , 117.17 , 117.23 , 117.3 , 
 118.76 , 118.84 , 118.9 , 119.0 , 125.3 , 125.4 , 125.5 , 128.1 , 128.3 , 128.4 , 
 128.5 , 129.77 , 129.8 , 129.9 , 131.85 , 131.90 , 133.2 , 133.3 , 139.5 , 
 139.7 , 139.8 , 160.68 , 160.70 , 160.9 , 165.25 , 165.33 , 172.6 , 172.7 , 
 172.76 , 172.79 , 173.01 , 173.02 . maldi - tof ( m / z ) : calcd for c63h90n2o16 1130.63 , found 1153.42 [ m + na ] , 1169.39 [ m 
 + k ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c63h91n2o16 1131.63623 , found 1131.63613 . p - toluenesulfonic acid ( 0.033 g , 0.175 mmol ) was added to a solution 
 of 1-benzyloxycarbonyl-5,6-dimethoxycarbonyl-4,5,6,7-dihydro-2h - isoindole ( 1.3 g , 3.5 mmol ) 
 and dimethoxymethane ( 0.133 g , 1.75 mmol ) in acetic acid ( 25 ml ) , 
 and the reaction mixture was stirred at room temperature under ar 
 for 24 h. the mixture was poured into cold water ( 80 ml ) , and the 
 formed precipitate was collected by filtration and dried in vacuum . the resulting solid was dissolved in meoh ( 20 ml ) and precipitated 
 upon addition of water ( 1015 ml ) at 0 c . the precipitate 
 was collected by centrifugation , washed with water ( 3  20 ml ) , 
 and dried in vacuum to give the title compound as a white solid ( mp 
 104106 c ) . h nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 2.652.78 
 ( 2h , m , chh ) , 2.903.03 ( 2h , 
 m , chh ) , 3.043.24 ( 6h , m , 
 chh , ch ) , 
 3.263.38 ( 2h , m , ch ) , 3.623.69 
 ( 12h , m , och3 ) , 3.693.81 
 ( 2h , m , ch2 ) , 5.175.33 
 ( 4h , m , ch2ph ) , 7.257.34 
 ( 10h , m , ar ) , 9.309.48 ( 2h , m , nh ) . c nmr ( cdcl3 )  ( ppm ) ( mixture 
 of conformers ) : 21.80 , 21.87 , 21.92 , 21.98 , 22.4 , 22.5 , 22.6 , 23.7 , 
 23.76 , 23.83 , 23.9 , 24.0 , 40.7 , 40.8 , 51.4 , 51.95 , 52.00 , 65.7 , 65.8 , 
 116.42 , 116.48 , 116.54 , 116.58 , 126.2 , 126.5 , 126.6 , 127.66 , 127.68 , 
 127.71 , 127.90 , 127.92 , 128.0 , 128.4 , 128.5 , 129.15 , 129.24 , 136.2 , 
 161.4 , 162.3 , 173.33 , 173.35 , 173.36 , 173.39 , 173.45 , 173.49 , 173.52 , 
 173.55 . maldi - tof ( m / z ) : calcd for 
 c41h42n2o12 754.27 , found 752.96 [ m  h ] , 776.95 [ m + na ] , 792.92 
 [ m + k ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c41h43n2o12 755.28099 , found 755.27822 . dipyrromethane 
 ester 5 ( 1.98 g , 1.75 mmol ) was dissolved in ch2cl2 ( 15 ml ) , and the solution was cooled to 0 c 
 on an ice bath . the ice bath was removed , and the reaction mixture was stirred 
 at room temperature for 1.5 h. the mixture was diluted with ch2cl2 ( 100 ml ) , washed with nahco3 ( 10% 
 aq . , 50 ml ) and brine ( 50 ml ) , and dried over na2so4 . the solvent was removed in vacuum , and the residue was purified 
 by column chromatography ( silica gel , ch2cl2/thf , gradient from 15:1 to 2:1 ) to give crude dipyrromethane 10 
 as a dark - brown oil ( 0.92 g ) . the thus - obtained crude dipyrromethane 
 10 was used immediately in the porphyrin synthesis ( see below ) . dipyrromethane 
 ester 6 ( 1.23 g , 1.63 mmol ) was dissolved in thf ( 50 
 ml ) , and the solution was purged with ar for 10 min . catalyst ( 0.2 g ) was added , and the reaction 
 mixture was purged with ar again for 10 min and then with h2 for 1520 min . the mixture was kept under vigorous stirring 
 overnight under h2 ( 1 atm ) . the mixture was purged with 
 ar and then passed through celite to remove the catalyst . the resulting 
 solution was concentrated in vacuum to give crude ,-bis(carboxy)methylenebis(1,1-(5,6-dibutoxycarbonyl-4,5,6,7-tetrahydro-2h - isoindole ) ) ( 6a ) ( 0.936 g ) as a slightly 
 pink viscous oil . maldi - tof ( m / z ) : calcd for c27h30n2o12 574.18 , found 596.90 [ m + na ] , 612.88 [ m + k ] . crude 6a ( 0.936 g , 1.63 mmol ) was dissolved 
 in thf ( 5 ml)/ch2cl2 ( 20 ml ) , and the solution 
 was cooled to 0 c on an ice bath . the ice bath was removed , and the reaction 
 mixture was stirred at room temperature for 1 h. the mixture was diluted 
 with ch2cl2 ( 100 ml ) , washed with nahco3 ( 10% aq . , 2  50 ml ) and brine ( 50 ml ) , and dried over 
 na2so4 . the solvent was removed in vacuum , and 
 the residue was purified on a short column ( silica gel , 10 cm , ch2cl2/thf , 25:1 ) to give crude dipyrromethane 11 
 ( 0.42 g ) as a dark - brown oil . maldi - tof ( m / z ) : calcd for c25h30n2o8 486.20 , found 487.01 [ m + h ] . dipyrromethane 
 3 was prepared from 2-tert - butoxycarbonyl-4,7-dihydro-2h - isoindole ( 1.18 g , 
 5.4 mol ) and benzaldehyde ( 0.285 g , 2.7 mmol ) following the procedure 
 described above for dipyrromethane 5 . dipyrromethane 
 4 was prepared from 1-tert - butoxycarbonyl-4,7-dihydro-2h - isoindole ( 0.8672 g , 4 mmol ) and 3,5-dibutoxycarbonylbenzaldehyde 
 ( 0.606 g , 2 mmol ) following the procedure described above for dipyrromethane 5 . dipyrromethane 7 was prepared from 1-benzyloxycarbonyl-4,9-dihydro-2h - benzo[f]isoindole ( 1.175 d , 3.88 mmol ) 
 and 3,5-dibutoxycarbonylbenzaldehyde ( 0.593 g , 1.94 mmol ) following 
 the procedure described above for dipyrromethane 6 . maldi - tof ( m / z ) : calcd for c41h42n2o4 626.31 , found 627.13 
 [ m + h ] . to avoid degradation , dipyrromethanes 3 , 
 4 , 7 , 8 , 9 , and 12 were 
 immediately introduced into their respective subsequent syntheses 
 without purification . 1 ( 0.5664 g , 1.44 mmol ) and 8 ( 0.47 g , 
 1.44 mmol ) were dissolved in methanol ( 145 ml ) , and the reaction mixture 
 was purged with ar . an excess of zn(oac)22h2o ( 3.1409 g , 14.4 mmol ) was added , and the reaction mixture was refluxed 
 for 2 h , during which time the solution color turned deep red . after 
 2 h , the reaction mixture was cooled to room temperature , and ddq 
 ( 0.9820 g , 4.3 mmol ) was added . the methanol was evaporated under reduced pressure , and the product 
 was purified by column chromatograpy ( silica gel , ch2cl2 ) . the fraction containing the target porphyrin ( as monitored 
 by uv  vis spectroscopy ) was collected and evaporated to dryness 
 to give crude zn13 . zn13 ( 0.14 g , 0.2 mmol ) 
 was treated with ddq ( 0.145 g , 0.64 mmol ) in refluxing thf ( 200 ml ) 
 during 30 min . the 
 reaction mixture was concentrated in vacuum and subjected to column 
 chromatography ( silica gel , ch2cl2 ) . after solvent 
 removal and drying in vacuum , zn18 was isolated 
 as a purple crystalline powder . uv  vis ( thf ) max ( nm ) : 427 , 561 , 599 . h nmr ( cdcl3 )  ( ppm ) : 4.11 ( 3h , s , och3 ) , 7.09 ( 2h , d , j = 8.0 hz , bn ) , 7.59 ( 2h , dd , j1 = j2 = 7.5 hz , bn ) , 7.877.95 ( 4h , m , bn , 
 ph ) , 8.018.09 ( 3h , m , ph ) , 8.19 ( 2h , d , j = 8.3 hz , ar ) , 8.40 ( 2h , d , j = 8.3 hz , ar ) , 8.82 ( 2h , d , j = 4.3 
 hz , pyr ) , 9.07 ( 2h , d , j = 4.3 hz , pyr ) , 
 9.25 ( 2h , d , j = 7.5 hz , bn ) , 
 10.20 ( 2h , s , meso - h ) . maldi - tof 
 ( m / z ) : calcd for c42h26n4o2zn 684.07 , found 684.36 [ m ] . zn18 ( 0.020 g , 0.029 mmol ) was 
 dissolved in 
 ch2cl2 ( 35 ml ) , and the mixture was shaken with 
 hcl ( 20% aq . , 2  35 ml ) in a separatory funnel . the organic 
 layer was washed with water ( 30 ml ) and dried over na2so4 . the solvent was removed in vacuum , and the solid was subjected 
 to column chromatography ( silica gel , ch2cl2 ) . target porphyrin 18 was isolated as a purple crystalline 
 powder ( mp > 300 c ) . vis ( thf ) 
 max ( nm ) : 420 , 527 , 560 , 585 , 641 . h 
 nmr ( cdcl3 )  ( ppm ) : 2.00 to 1.91 
 ( 1h , m , broad ) , 1.71 to 1.58 ( 1h , m , broad ) , 4.14 
 ( 3h , s , och3 ) , 7.33 ( 2h , d , j = 8.1 hz , ph ) , 7.71 ( 2h , dd , j1 = 7.9 , j2 = 7.3 hz , bn ) , 7.95 ( 2h , dd , j1 = 7.4 , j2 = 7.3 hz , bn ) , 8.018.08 ( 3h , 
 m , ph ) , 8.178.23 ( 2h , m , bn ) , 8.328.38 
 ( 2h , m , ar ) , 8.468.51 ( 2h , m , ar ) , 8.898.95 ( 2h , m , 
 pyr ) , 9.249.29 ( 2h , m , pyr ) , 9.429.49 ( 2h , m , bn ) , 
 10.4710.53 ( 2h , m , meso - h ) . c nmr ( cdcl3 )  ( ppm ) : 52.5 , 99.1 , 
 114.7 , 120.4 , 120.9 , 125.5 , 127.6 , 127.6 , 128.3 , 129.2 , 129.3 , 129.6 , 
 129.9 , 130.0 , 132.8 , 134.5 , 137.5 , 139.9 , 140.3 , 141.3 , 144.6 , 144.8 , 
 144.9 , 145.8 , 167.4 . maldi - tof ( m / z ) : calcd for c42h28n4o2 620.22 , found 621.69 [ m + h ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c42h29n4o2 621.22848 , found 
 621.22687 . 2 ( 0.373 g , 0.67 mmol ) and 
 9 ( 0.350 g , 0.67 mmol ) were dissolved in benzene ( 65 ml ) , and the 
 solution was purged with ar . zn(oac)22h2o was added in excess ( 1.45 g , 6.7 mmol ) , and the mixture was heated 
 under reflux with a dean  stark trap for 2 h under ar . the reaction 
 mixture was purged with air , and the refluxing was continued under 
 air for 12 h. the reaction progress was monitored by uv the solvent was removed in vacuum , and the remaining 
 material was subjected to column chromatography ( silica gel , ch2cl2/etoac = 20:1 ) . the band containing the target 
 porphyrin was collected , and the solvent was removed in vacuum to 
 give crude zn14 . zn14 ( 0.205 g , 0.2 mmol ) was 
 dissolved in thf ( 50 ml ) , and ddq ( 0.095 g , 0.42 mmol ) was added . the reaction mixture was heated under reflux for 40 min , and the reaction 
 progress was monitored by uv  vis spectroscopy . the solvent 
 was removed under vacuum , and the residue was diluted with ch2cl2 ( 100 ml ) , washed with na2so3 ( 2  50 ml ) and water , and dried over na2so4 . the solution was concentrated , and the product was 
 purified by column chromatography ( silica gel , ch2cl2/etoac = 20:1 ) to give porphyrin zn19 as a purple crystalline powder . uv  vis ( thf ) max ( nm ) : 430 , 561 , 597 . maldi - tof 
 ( m / z ) : calcd for c60h56n4o8zn 1024.34 , found 1024.35 [ m ] . zn19 ( 0.200 g , 0.195 mmol ) was 
 dissolved in 
 ch2cl2 ( 150 ml ) . ( 20% , 2  100 ml ) and then water ( 100 ml ) 
 and dried over na2so4 . the solvent was removed 
 in vacuum , and the product was purified by column chromatography ( silica 
 gel , ch2cl2/etoac = 20:1 ) and further by reprecipitation 
 from ch2cl2 upon addition of meoh / h2o ( 50:0.5 v / v ) . the precipitate was isolated by centrifugation , 
 washed with meoh , and dried in vacuum to give the title compound as 
 a purple crystalline powder ( mp 274275 c ) . vis ( thf ) max ( nm ) : 421 , 529 , 
 562 , 584 , 640 . h nmr ( cdcl3 )  ( ppm ) : 
 2.04 to 1.52 ( 2h , m , broad ) , 0.89 ( 6h , t , j = 7.4 hz , ch3 ) , 0.96 ( 6h , t , j = 7.4 hz , ch3 ) , 1.361.54 ( 8h , m , ch2 ) , 1.701.85 ( 8h , m , ch2 ) , 4.42 ( 4h , t , j = 6.7 hz , och2 ) , 
 4.48 ( 4h , t , j = 6.7 hz , och2 ) , 7.23 ( 2h , d , j = 8.1 hz , bn ) , 7.74 ( 2h , dd , j1 = j2 = 7.3 hz , bn ) , 8.07 ( 2h , dd , j1 = j2 = 7.3 hz , bn ) , 8.87 ( 2h , d , j = 4.4 hz , pyr ) , 9.099.13 ( 4h , m , ar ) , 9.159.18 
 ( 1h , m , ar ) , 9.30 ( 2h , d , j = 4.4 hz , 
 pyr ) , 9.429.45 ( 1h , m , ar ) , 9.48 ( 2h , d , j = 7.9 hz , bn ) , 10.53 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  
 ( ppm ) : 13.69 , 13.74 , 19.2 , 19.3 , 30.6 , 30.8 , 65.6 , 65.8 , 99.4 , 112.2 , 
 119.5 , 121.1 , 124.9 , 127.7 , 127.9 , 130.0 , 130.06 , 130.14 , 130.3 , 131.6 , 
 131.9 , 137.1 , 137.5 , 138.4 , 139.9 , 140.3 , 141.6 , 142.3 , 144.5 , 144.9 , 
 145.1 , 165.8 , 166.1 . maldi - tof ( m / z ) : calcd for c60h58n4o8 962.43 , found 963.11 [ m + h ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c60h59n4o8 963.43269 , found 
 963.43134 . zn17 was prepared similarly to 
 zn14 ( see the synthesis of zn19 above ) 
 from 2 ( 0.316 g , 0.56 mmol ) and 12 ( 0.353 g , 0.56 mmol ) . the reaction was complete in 18 h. zn17 was purified by column 
 chromatography ( silica gel , ch2cl2/thf = 70:1 ) . maldi - tof ( m / z ) : calcd for c68h64n4o8zn 1128.40 , found 
 1128.52 [ m ] . zn17 ( 0.09 g , 0.08 mmol ) was 
 dissolved in ch2cl2 ( 30 ml ) , and ddq ( 0.038 
 g , 0.168 mmol ) was added . the reaction mixture was stirred for 10 
 min at room temperature and was monitored by uv  vis spectroscopy . the solvent was removed in vacuum , and the remaining material was 
 dissolved in ch2cl2 ( 100 ml ) , washed with na2so3 ( 2  50 ml ) and water ( 50 ml ) , and dried 
 over na2so4 . the mixture was chromatographed 
 ( silica gel , ch2cl2/thf = 70:1 ) , and zn22 was isolated as a green crystalline powder . vis ( thf ) max ( nm ) : 
 452 , 583 , 623 . maldi - tof ( m / z ) : 
 calcd for c68h60n4o8zn 
 1124.37 , found 1124.05 [ m ] . zn22 ( 0.080 g , 0.071 mmol ) was dissolved in 
 ch2cl2 ( 100 ml ) , and the solution was shaken 
 with hcl aq . ( 10% , 4  100 ml ) in a separatory funnel , washed 
 with water ( 100 ml ) , and dried over na2so4 . the solvent was removed in vacuum , and the product was purified by 
 column chromatography ( silica gel , ch2cl2/thf 
 = 70:1 ) . the title porphyrin 22 was precipitated from 
 ch2cl2/thf solution upon addition of meoh ( 1:100 
 v / v ) and isolated as a green crystalline powder ( mp 286288 
 c ) . vis ( thf ) max ( nm ) : 422 , 454 , 521 , 560 , 594 , 661 . h nmr ( cdcl3 )  ( ppm ) : 0.72 ( 1h , broad ) , 0.25 ( 1h , 
 broad ) , 0.83 ( 6h , t , j = 7.4 hz , ch3 ) , 0.96 ( 6h , t , j = 7.4 hz , ch3 ) , 1.311.43 
 ( 4h , m , ch2 ) , 1.441.55 
 ( 4h , m , ch2 ) , 1.651.76 
 ( 4h , m , ch2 ) , 1.761.86 
 ( 4h , m , ch2 ) , 4.41 ( 4h , 
 t , j = 6.7 hz , och2 ) , 4.47 ( 4h , t , j = 6.7 hz , och2 ) , 7.59 
 ( 2h , s ) , 7.67 ( 2h , dd , j1 = 
 7.4 , j2 = 7.0 hz ) , 7.76 ( 2h , 
 dd , j1 = 7.4 , j2 = 6.9 hz ) , 7.88 ( 2h , d , j = 8.1 hz ) , 8.44 ( 2h , d , j = 8.1 hz ) , 8.66 ( 2h , d , j = 4.3 hz , 
 pyr ) , 9.05 ( 2h , d , j = 1.4 hz , ar ) , 9.07 
 ( 2h , d , j = 4.3 hz , pyr ) , 9.12 ( 1h , dd , j1 = j2 = 1.4 hz , ar ) , 9.17 ( 2h , d , j = 1.4 hz , ar ) , 9.59 ( 1h , dd , j1 = j2 = 1.5 hz , ar ) , 
 9.82 ( 2h , s ) , 10.33 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  ( ppm ) : 13.7 , 13.8 , 
 19.2 , 19.3 , 30.6 , 30.8 , 65.6 , 65.8 , 98.3 , 110.2 , 119.7 , 121.0 , 125.3 , 
 126.2 , 127.1 , 128.6 , 129.0 , 129.7 , 130.1 , 130.2 , 130.3 , 131.5 , 132.5 , 
 132.57 , 132.63 , 135.1 , 137.7 , 138.1 , 138.2 , 141.3 , 141.5 , 142.6 , 144.0 , 
 145.5 , 146.5 . maldi - tof ( m / z ) : calcd 
 for c68h62n4o8 1062.46 , 
 found 1063.21 [ m + h ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c68h63n4o8 1063.46399 , found 1063.46533 . zn15 was synthesized 
 similarly to porphyrin zn14 ( see the synthesis of zn19 above ) from 2 ( 0.554 g , 1 mmol ) and 10 ( 0.92 
 g , 1 mmol ) . the reaction was complete in 16 h. the product was purified 
 by column chromatography ( silica gel , ch2cl2/etoac = 20:1 ) to give the title compound zn15 as a purple solid . maldi - tof ( m / z ) : calcd for c80h96n4o16zn 1432.61 , found 1432.87 [ m ] . zn15 ( 0.300 g , 0.21 mmol ) was dissolved in ch2cl2 ( 200 ml ) , and the solution was shaken with 
 hcl aq . ( 20% , 2  100 ml ) in a separatory funnel , washed with 
 water ( 100 ml ) , and dried over na2so4 . the solvent 
 was removed in vacuum , and the product was purified by column chromatography 
 ( silica gel , ch2cl2/etoac = 20:1 ) and further 
 by reprecipitation from ch2cl2 upon addition 
 of meoh . the precipitate was isolated by centrifugation , washed with 
 meoh , and dried in vacuum to give the title compound as a purple crystalline 
 powder ( mp 140142 c ) . vis 
 ( thf ) max ( nm ) : 409 , 504 , 535 , 575 , 629 . h nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 3.02 
 to 2.58 ( 2h , m , broad ) , 0.581.01 ( 24h , m , ch3 ) , 1.041.19 and 1.331.86 ( 32h , 
 m , ch2 ) , 2.973.27 
 ( 4h , m , chh ) , 3.553.71 ( 4h , 
 m , chh ) , 3.834.02 ( 4h , m , 
 och2 ) , 4.174.27 
 ( 4h , m , och2 ) , 4.404.49 
 ( 8h , m , och2 ) , 4.494.72 
 ( 4h , m , ch ) , 8.94 ( 2h , d , j = 4.5 hz , pyr ) , 8.948.96 ( 1h , m , ar ) , 
 8.979.00 ( 1h , m , ar ) , 9.079.12 ( 2h , m , ar ) , 9.139.16 
 ( 1h , m , ar ) , 9.209.24 ( 1h , m , ar ) , 9.38 ( 2h , d , j = 4.5 hz , pyr ) , 10.2310.24 ( 2h , m , meso - h ) . c nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 13.3 , 13.4 , 13.67 , 13.70 , 
 13.74 , 13.77 , 13.77 , 13.78 , 18.75 , 18.84 , 19.14 , 19.17 , 19.21 , 19.27 , 
 19.31 , 22.7 , 24.0 , 24.3 , 28.1 , 28.5 , 29.7 , 30.27 , 30.34 , 30.63 , 30.65 , 
 30.74 , 40.7 , 40.8 , 41.8 , 41.9 , 64.6 , 64.7 , 64.9 , 65.56 , 65.66 , 65.72 , 
 101.6 , 115.0 , 115.1 , 117.3 , 129.1 , 129.2 , 130.03 , 130.04 , 130.06 , 
 130.5 , 130.6 , 130.7 , 131.1 , 131.8 , 136.6 , 136.8 , 137.0 , 137.1 , 138.59 , 
 138.60 , 140.0 , 140.1 , 141.8 , 142.0 , 142.3 , 144.8 , 144.9 , 146.3 , 165.5 , 
 165.8 , 166.0 , 166.1 , 172.5 , 172.6 , 173.1 , 173.3 . maldi - tof ( m / z ) : calcd for c80h98n4o16 1370.70 , found 1371.14 [ m + h ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c80h99n4o16 1371.70497 , found 1371.70702 . zn16 was synthesized 
 similarly to porphyrin zn14 ( see the synthesis of zn19 above ) from 2 ( 0.484 g , 0.86 mmol ) and 11 
 ( 0.42 g , 0.86 mmol ) . the reaction was complete in 12 h. the product 
 was purified by column chromatography ( silica gel , ch2cl2/thf , gradient from 50:1 to 25:1 ) . maldi - tof ( m / z ) : calcd for c52h52n4o12zn 988.29 , found 
 987.93 [ m ] . zn16 ( 0.200 g , 
 0.2 mmol ) was dissolved in ch2cl2 ( 200 ml ) , 
 and the solution was shaken with hcl aq . ( 20% , 2  100 ml ) in 
 a separatory funnel , washed with water ( 100 ml ) , and dried over na2so4 . the solvent was removed in vacuum , and the 
 product was purified by column chromatography ( silica gel , ch2cl2/thf = 5:1 ) and further by reprecipitation from 
 ch2cl2/thf ( 1:1 ) upon addition of meoh . the 
 precipitate was isolated by centrifugation , washed with meoh , and 
 dried in vacuum to give the title compound as a brown crystalline 
 powder ( mp 287288 c ) . yield 0.182 g ( 98% ) . vis 
 ( dma ) max ( nm ) : 404 , 499 , 531 , 568 , 623 . h nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 3.75 
 to 3.17 ( 2h , m , broad ) , 0.901.04 ( 6h , m , ch3 ) , 1.421.53 ( 4h , m , ch2 ) , 1.741.85 ( 4h , m , ch2 ) , 3.623.99 ( 4h , m , chh ) , 3.76 ( 3h , s , och3 ) , 3.77 ( 3h , s , och3 ) , 
 3.80 ( 3h , s , och3 ) , 3.82 ( 3h , 
 s , och3 ) , 4.074.28 ( 4h , 
 m , chh ) , 4.394.49 ( 4h , m , 
 och2 ) , 4.504.65 
 ( 4h , m , ch ) , 8.89 ( 1h , d , j = 4.5 hz , pyr ) , 8.90 ( 1h , d , j = 4.5 hz , pyr ) , 9.069.12 ( 2h , m , ar ) , 9.139.17 
 ( 1h , m , ar ) , 9.33 ( 1h , d , j = 4.5 hz , 
 pyr ) , 9.34 ( 1h , d , j = 4.5 hz , pyr ) , 
 9.649.79 ( 1h , m , meso - h ) , 
 10.05 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 13.7 , 
 13.8 , 19.25 , 19.27 , 23.7 , 23.9 , 24.0 , 30.7 , 30.8 , 40.87 , 40.90 , 41.05 , 
 41.07 , 52.19 , 52.23 , 65.6 , 95.59 , 95.63 , 101.1 , 101.2 , 117.82 , 117.83 , 
 129.8 , 130.1 , 130.5 , 130.8 , 136.6 , 136.7 , 138.39 , 138.42 , 142.56 , 
 142.59 , 166.1 , 166.2 , 173.36 , 173.38 , 173.44 . maldi - tof ( m / z ) : calcd for c52h54n4o12 926.37 , found 927.13 [ m + h ] , 965.07 
 [ m + k ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c52h55n4o12 927.38102 , found 927.38357 . a free - base porphyrin , platinum(ii ) 
 acetylacetonate , and benzoic acid were mixed together and heated to 
 130140 c under ar . the reaction progress was monitored 
 by uv  vis spectroscopy ; samples were analyzed every 15 min . the reaction was stopped after the q00 band maximum of 
 the free - base porphyrin disappeared . the mixture was dispersed in 
 meoh / h2o ( 2:1 , 50 ml ) , and the precipitate , which 
 contained the target pt porphyrin , was isolated by centrifugation . it was redispersed in meoh / h2o ( 2:1 , 20 ml ) and 
 centrifuged again . this washing procedure was repeated three times , 
 after which the final solid was dried in vacuum . the product was purified 
 by column chromatography , and the fraction containing the target compound 
 was collected . the solvent was removed in vacuum , and the target metalloporphyrin 
 was reprecipitated from ch2cl2 by addition of 
 meoh . a free - base porphyrin was dissolved 
 in dry benzonitrile 
 ( 24 ml ) , and the solution was placed into a thick - walled 
 microwave vial ( biotage , 5 ml ) . platinum(ii ) acetylacetonate or palladium(ii ) 
 acetate was added , and the vessel was sealed , after which the mixture 
 was subjected to microwave irradiation at 250 c ( 2 bar , 
 105145 w ) for 40 min under stirring . the reaction progress 
 was monitored by uv  vis spectroscopy ; samples were analyzed 
 every 20 min . the reaction was stopped after the q00 band 
 maximum of the free - base porphyrin disappeared . after the mixture 
 was cooled , benzonitrile was removed in vacuum , and the product was 
 purified by column chromatography on silica gel . the fraction containing 
 the target compound was collected , and the solvent was removed in 
 vacuum . the target metalloporphyrin was reprecipitated from ch2cl2 upon addition of meoh , and the precipitate 
 was collected by centrifugation and dried in vacuum . pt15 was synthesized 
 from 15 ( 0.153 g , 0.108 mmol ) and pt(acac)2 ( 0.170 g , 0.433 mmol ) in benzoic acid ( 3 g ) . the reaction was complete 
 in 6 h. chromatography was performed using ch2cl2/thf ( 50:1 ) . the target compound was isolated as an orange solid 
 ( mp 157160 c ) . vis ( thf ) 
 max ( nm ) : 391 , 503 , 535 . h nmr ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 0.591.01 
 ( 24h , m , ch3 ) , 1.041.19 
 and 1.341.86 ( 32h , m , ch2 ) , 2.873.12 ( 4h , m , chh ) , 
 3.483.63 ( 4h , m , chh ) , 3.864.02 
 ( 4h , m , och2 ) , 4.174.59 
 ( 16h , m , och2 , ch ) , 8.79 ( 2h , d , j = 
 4.9 hz , pyr ) , 8.908.94 ( 2h , m , ar ) , 8.989.06 ( 2h , 
 m , ar ) , 9.129.16 ( 1h , m , ar ) , 9.199.25 ( 3h , m , ar , 
 pyr ) , 10.0310.08 ( 2h , m , meso - h ) . c nmr ( cdcl3 )  ( ppm ) ( mixture of 
 conformers ) : 13.37 , 13.44 , 13.68 , 13.70 , 13.73 , 13.76 , 13.78 , 18.76 , 
 18.83 , 19.15 , 19.18 , 19.20 , 19.26 , 19.31 , 23.68 , 23.71 , 23.99 , 28.82 , 
 29.16 , 29.69 , 30.30 , 30.36 , 30.63 , 30.65 , 30.73 , 40.36 , 40.41 , 41.86 , 
 41.94 , 64.6 , 64.7 , 64.9 , 65.6 , 65.7 , 65.8 , 104.0 , 117.3 , 177.4 , 119.4 , 
 129.8 , 129.9 , 130.3 , 130.5 , 130.6 , 130.7 , 131.2 , 131.3 , 136.6 , 136.7 , 
 137.0 , 137.1 , 137.2 , 137.8 , 138.3 , 138.4 , 138.6 , 138.7 , 139.1 , 139.2 , 
 139.4 , 140.5 , 141.70 , 141.79 , 141.83 , 165.5 , 165.7 , 166.0 , 166.1 , 
 172.5 , 172.6 , 173.1 , 173.2 . hrms ( esi - tof ) m / z : [ m + h ] calcd for c80h97n4o16pt 1565.65650 , found 1565.65826 . pt15 was synthesized 
 from 15 ( 0.065 g , 0.0475 mmol ) and pt(acac)2 ( 0.056 g , 0.143 mmol ) . pd15 was synthesized 
 from 15 ( 0.017 g , 0.0124 mmol ) and pd(oac)2 ( 0.011 g , 0.05 mmol ) . chromatography 
 was performed using ch2cl2/thf ( 50:1 ) to give 
 crude pd15 ( 0.018 g ) , which was used in the subsequent 
 aromatization reaction without further purification . pt16 was synthesized 
 from 16 ( 0.05 g , 0.054 mmol ) and pt(acac)2 ( 0.085 g , 0.22 mmol ) . pt16 was isolated as an orange 
 crystalline solid ( mp > 300 c ) . vis 
 ( dma ) max ( nm ) : 384 , 500 , 531 . h nmr 
 ( cdcl3 )  ( ppm ) ( mixture of conformers ) : 0.881.00 
 ( 6h , m , ch3 ) , 1.421.54 
 ( 4h , m , ch2 ) , 1.711.87 
 ( 4h , m , ch2 ) , 2.993.52 
 ( 8h , m , chh ) , 3.71 ( 3h , s , och3 ) , 3.75 ( 3h , s , och3 ) , 3.76 ( 3h , s , och3 ) , 3.79 ( 3h , s , och3 ) , 4.064.34 
 ( 4h , m , ch ) , 4.404.53 ( 4h , 
 m , och2 ) , 8.78 ( 1h , d , j = 4.8 hz , pyr ) , 8.79 ( 1h , d , j = 4.9 hz , pyr ) , 8.848.91 and 8.969.00 
 ( 2h , m , ar ) , 9.079.11 ( 1h , m , ar ) , 9.129.20 ( 3h , m , 
 ar , pyr ) , 9.219.29 and 9.489.63 ( 2h , m , meso - h ) , 9.71 ( 1h , s , broad , meso - h ) . the c nmr spectrum was not recorded because 
 of the low solubility . maldi - tof ( m / z ) : calcd for c52h52n4o12pt 1119.32 , found 1119.73 [ m ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c52h53n4o12pt 1120.33057 , found 
 1120.33205 . pd16 was synthesized 
 from 16 ( 0.015 g , 0.0162 mmol ) and pd(oac)2 ( 0.0145 g , 0.065 mmol ) . chromatography 
 was performed using ch2cl2/thf ( 25:1 ) to give 
 crude pd16 ( 0.0165 g ) , which was used in the 
 aromatization step without further purification ( see below ) . pt18 was synthesized 
 from 18 ( 0.015 g , 0.026 mmol ) and pt(acac)2 ( 0.041 g , 0.1 mmol ) in benzoic acid ( 1.5 g ) . the target compound was isolated as a pink crystalline powder ( mp 
 > 300 c ) . uv  vis ( dma ) max / nm ( log   ) : 401 ( 5.33 ) , 519 ( 4.19 ) , 556 ( 4.91 ) . h nmr ( cdcl3 )  ( ppm ) : 4.13 ( 3h , s , och3 ) , 7.04 ( 2h , d , j = 8.3 hz , bn ) , 7.58 ( 2h , dd , j1 = 8.0 , j2 = 7.8 hz , bn ) , 7.897.96 ( 4h , m , bn , 
 ph ) , 8.028.12 ( 3h , m , ph ) , 8.26 ( 2h , d , j = 8.2 hz , ar ) , 8.46 ( 2h , d , j = 8.2 hz , ar ) , 8.82 ( 2h , d , j = 4.7 
 hz , pyr ) , 9.16 ( 2h , d , j = 4.7 hz , pyr ) , 
 9.25 ( 2h , d , j = 7.8 hz , bn ) , 
 10.39 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  ( ppm ) : 52.5 , 101.4 , 114.5 , 119.9 , 
 122.1 , 125.9 , 127.2 , 127.3 , 128.2 , 128.6 , 129.37 , 129.43 , 129.8 , 130.4 , 
 130.5 , 132.5 , 133.8 , 136.3 , 137.5 , 139.2 , 139.4 , 140.2 , 141.5 , 145.9 , 
 167.3 . maldi - tof ( m / z ) : calcd for 
 c42h26n4o2pt 813.17 , found 
 813.41 [ m ] . hrms ( esi - tof ) m / z : [ m ] calcd for c42h26n4o2pt 813.17012 , found 813.16860 . pt19 was synthesized 
 from 19 ( 0.12 g , 0.132 mmol ) and pt(acac)2 ( 0.21 g , 0.53 mmol ) in benzoic acid ( 2.00 g , 16.4 mmol ) . the reaction 
 was complete in 6 h. chromatography was performed using ch2cl2/thf = 50:1 . the target compound was isolated as a 
 dark - red crystalline powder ( mp > 300 c ) . uv  vis ( dma ) max / nm ( log   ) : 402 
 ( 5.34 ) , 521 ( 4.16 ) , 559 ( 4.92 ) . h nmr ( cdcl3 )  ( ppm ) : 0.87 ( 6h , t , j = 7.4 
 hz , ch3 ) , 0.94 ( 6h , t , j = 7.4 hz , ch3 ) , 1.351.51 ( 8h , m , ch2 ) , 1.681.83 ( 8h , m , ch2 ) , 4.41 ( 4h , t , j = 6.7 
 hz , och2 ) , 4.45 ( 4h , t , j = 6.7 hz , och2 ) , 6.96 ( 2h , d , j = 8.0 
 hz , bn ) , 7.60 ( 2h , dd , j1 = j2 = 7.5 hz , 
 bn ) , 7.96 ( 2h , dd , j1 = j2 = 7.2 hz , bn ) , 
 8.78 ( 2h , d , j = 3.5 hz , pyr ) , 9.03 ( 2h , 
 d , j = 1.6 hz , ar ) , 9.07 ( 2h , d , j = 1.6 hz , ar ) , 9.15 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 9.22 ( 2h , d , j = 3.6 hz , pyr ) , 9.31 ( 2h , d , j = 7.5 
 hz , bn ) , 9.44 ( 1h , dd , j1 = j2 = 1.6 hz , 
 ar ) , 10.50 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  ( ppm ) : 13.7 , 13.8 , 19.2 , 
 19.3 , 30.6 , 30.8 , 65.6 , 65.8 , 101.4 , 114.5 , 120.1 , 120.5 , 125.2 , 127.4 , 
 127.5 , 128.7 , 129.8 , 130.1 , 130.3 , 131.7 , 132.1 , 136.1 , 137.1 , 137.1 , 
 137.4 , 137.7 , 138.1 , 139.1 , 140.1 , 141.7 , 142.4 , 165.8 , 166.1 . maldi - tof 
 ( m / z ) : calcd for c60h56n4o8pt 1155.37 , found 1155.01 [ m ] . hrms ( esi - tof ) m / z : [ m ] calcd for c60h56n4o8pt 1155.37445 , found 1155.37554 . pt19 was synthesized 
 from 19 ( 0.02 g , 0.021 mmol ) and pt(acac)2 ( 0.024 g , 0.062 mmol ) and purified as in method 1 above . pd19 was synthesized 
 from 19 ( 0.01 g , 0.01 mmol ) and pd(oac)2 ( 0.0093 
 g , 0.042 mmol ) . pd19 was isolated as a dark - purple 
 crystalline solid ( mp 296297 c ) . uv  vis ( dma ) max ( nm ) : 417 , 534 , 570 . h nmr ( cdcl3 )  ( ppm ) : 0.88 ( 6h , t , j = 7.4 hz , ch3 ) , 0.95 ( 6h , t , j = 7.4 hz , ch3 ) , 1.351.54 ( 8h , m , ch2 ) , 1.681.84 ( 8h , m , ch2 ) , 4.41 ( 4h , t , j = 6.8 hz , och2 ) , 
 4.46 ( 4h , t , j = 6.7 hz , och2 ) , 7.01 ( 2h , d , j = 8.1 hz , bn ) , 7.62 ( 2h , dd , j1 = 7.8 , j2 = 7.4 hz , bn ) , 7.95 ( 2h , dd , j1 = j2 = 7.4 hz , bn ) , 8.76 ( 2h , d , j = 4.6 hz , pyr ) , 9.03 ( 2h , d , j = 1.6 hz , ar ) , 9.07 ( 2h , d , j = 1.6 
 hz , ar ) , 9.139.19 ( 3h , m , pyr , ar ) , 9.29 ( 2h , d , j = 7.8 hz , bn ) , 9.44 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 10.42 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  ( ppm ) : 
 13.69 , 13.74 , 19.2 , 19.3 , 30.6 , 30.8 , 65.6 , 65.8 , 101.2 , 114.6 , 120.0 , 
 120.3 , 125.1 , 127.3 , 127.4 , 129.4 , 129.8 , 130.2 , 130.6 , 131.7 , 132.0 , 
 136.9 , 137.5 , 137.7 , 137.8 , 138.6 , 138.7 , 139.4 , 140.8 , 142.1 , 142.8 , 
 165.8 , 166.1 . maldi - tof ( m / z ) : calcd 
 for c60h56n4o8pd 1066.31 , 
 found 1065.90 [ m ] . hrms ( esi - tof ) m / z : [ m ] calcd for c60h56n4o8pd 1066.31478 , found 1066.31410 . pt22 was synthesized 
 from 22 ( 0.032 g , 0.03 mmol ) and pt(acac)2 ( 0.05 g , 0.12 mmol ) in benzoic acid ( 2 g ) . the target compound was isolated as a dark - green crystalline powder 
 ( mp > 300 c ) . uv  vis ( dma ) max / nm ( log   ) : 423 ( 5.02 ) , 549 ( 4.16 ) , 593 ( 4.93 ) . h nmr ( cdcl3 )  ( ppm ) : 0.81 ( 6h , t , j = 7.3 hz , ch3 ) , 0.95 ( 6h , t , j = 7.3 hz , ch3 ) , 1.301.41 ( 4h , m , ch2 ) , 1.411.53 ( 4h , m , ch2 ) , 1.651.74 ( 4h , m , ch2 ) , 1.751.84 ( 4h , m , ch2 ) , 4.40 ( 4h , t , j = 6.7 hz , och2 ) , 
 4.46 ( 4h , t , j = 6.7 hz , och2 ) , 7.357.43 ( 2h , m , broad ) , 
 7.607.67 ( 2h , m , broad ) , 7.697.76 ( 2h , m , broad ) , 
 7.767.83 ( 2h , m , broad ) , 8.368.40 ( 2h , m , broad ) , 
 8.67 ( 2h , m , broad ) , 9.02 ( 2h , d , j = 
 1.5 hz , ar ) , 9.11 ( 2h , m , broad ) , 9.15 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 9.17 ( 2h , d , j = 1.5 
 hz , ar ) , 9.63 ( 1h , dd , j1 = j2 = 1.5 hz , ar ) , 9.72 ( 2h , s , 
 broad ) , 10.46 ( 2h , s , broad , meso - h ) . hrms ( esi - tof ) m / z : [ m ] calcd for c68h60n4o8pt 1256.40747 , found 1256.40717 . pd22 was synthesized 
 from 22 ( 0.004 g , 0.0038 mmol ) and pd(oac)2 ( 0.0034 g , 0.015 mmol ) . pd22 was isolated as a dark - green crystalline powder ( mp > 300 
 c ) . vis ( dma ) max ( nm ) : 435 , 561 , 605 . h nmr ( cdcl3 )  
 ( ppm ) : 0.81 ( 6h , t , j = 7.4 hz , ch3 ) , 0.95 ( 6h , t , j = 7.4 hz , ch3 ) , 1.281.41 
 ( 4h , m , ch2 ) , 1.411.54 
 ( 4h , m , ch2 ) , 1.641.74 
 ( 4h , m , ch2 ) , 1.741.84 
 ( 4h , m , ch2 ) , 4.40 ( 4h , 
 t , j = 6.5 hz , och2 ) , 4.46 ( 4h , t , j = 6.6 hz , och2 ) , 7.427.49 
 ( 2h , m , broad ) , 7.607.69 ( 2h , m , broad ) , 7.707.78 
 ( 2h , m , broad ) , 7.807.87 ( 2h , m , broad ) , 8.388.47 
 ( 2h , m , broad ) , 8.668.74 ( 2h , m , broad ) , 9.009.05 
 ( 2h , m , broad ) , 9.109.20 ( 5h , m , broad ) , 9.609.66 
 ( 1h , m , broad ) , 9.739.82 ( 2h , m , broad ) , 10.4610.53 
 ( 2h , m , broad ) . the c nmr spectrum was not recorded because 
 of the low solubility . maldi - tof ( m / z ) : calcd for c68h60n4o8pd 1166.34 , found 1165.88 [ m ] . hrms ( esi - tof ) m / z : [ m ] calcd for c68h60n4o8pd 1166.34628 , found 1166.34671 . the porphyrin was dissolved 
 in toluene ( 50 ml ) , and ddq was added . the reaction mixture 
 was refluxed , and the reaction progress was monitored by uv the reaction was stopped when no further changes could 
 be observed in the spectra . the reaction mixture was diluted with 
 ch2cl2 ( 100 ml ) , washed with na2so3 ( 10% aqueous solution , 2  50 ml ) and water ( 50 ml ) , 
 and dried over na2so4 . the solvents were removed 
 in vacuum , and the product was purified by column chromatography on 
 silica gel . the fraction containing the target compound was collected , 
 and the solvent was removed in vacuum . the target metalloporphyrin 
 was reprecipitated from ch2cl2 upon addition 
 of meoh , and the precipitate was collected by centrifugation and dried 
 in vacuum . pt20 was synthesized from 
 pt15 ( 0.05 g , 0.033 mmol ) using ddq ( 0.03 g , 
 0.132 mmol ) . the reaction was complete in 10 h. chromatography was 
 performed using ch2cl2/thf = 50:1 . pt20 was isolated as a bright - purple crystalline solid ( mp 256258 
 c ) . uv  vis ( dma ) max / nm ( log   ) : 412 ( 5.43 ) , 527 ( 4.29 ) , 568 ( 5.01 ) . h nmr ( cdcl3 )  ( ppm ) : 0.87 ( 6h , t , j = 7.4 hz , ch3 ) , 0.95 ( 6h , t , j = 7.4 hz , ch3 ) , 1.05 ( 6h , t , j = 7.4 hz , ch3 ) , 1.10 ( 6h , t , j = 7.4 hz , ch3 ) , 1.341.62 ( 16h , m , ch2 ) , 1.691.92 ( 16h , m , ch2 ) , 4.35 ( 4h , t , j = 7.1 hz , och2 ) , 4.42 
 ( 4h , t , j = 6.8 hz , och2 ) , 4.46 ( 4h , t , j = 6.7 hz , och2 ) , 
 4.54 ( 4h , t , j = 6.8 hz , och2 ) , 7.55 ( 2h , s , bn ) , 
 8.85 ( 2h , d , j = 4.9 hz , pyr ) , 9.03 ( 2h , 
 d , j = 1.6 hz , ar ) , 9.07 ( 2h , d , j = 1.6 hz , ar ) , 9.17 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 9.31 ( 2h , d , j = 4.9 hz , pyr ) , 9.46 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 
 9.61 ( 2h , s , bn ) , 10.63 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  
 ( ppm ) : 13.66 , 13.73 , 13.79 , 13.83 , 19.16 , 19.17 , 19.26 , 19.32 , 30.63 , 
 30.68 , 30.73 , 65.65 , 65.68 , 65.8 , 66.1 , 103.3 , 116.0 , 120.8 , 121.4 , 
 126.9 , 129.4 , 130.1 , 130.4 , 130.6 , 131.4 , 132.2 , 132.3 , 132.7 , 135.4 , 
 136.7 , 137.1 , 137.5 , 137.6 , 139.1 , 140.3 , 140.9 , 141.1 , 141.2 , 165.2 , 
 165.9 , 166.7 , 168.8 . hrms ( esi - tof ) m / z : [ m + h ] calcd for c80h89n4o16pt 1557.59389 , found 1557.5965 . pd-20 was prepared 
 from pd15 ( 0.018 g , 0.012 mmol ) using ddq ( 0.011 
 g , 0.049 mmol ) . the reaction was complete in 8 h. chromatography was performed using 
 ch2cl2/thf = 50:1 . pd20 was isolated as a dark - purple crystalline solid ( mp 243245 
 c ) . vis ( dma ) max ( nm ) : 427 , 541 , 581 . h nmr ( cdcl3 )  ( ppm ) : 0.88 ( 6h , t , j = 7.4 hz , ch3 ) , 0.95 ( 6h , t , j = 7.4 hz , ch3 ) , 1.05 ( 6h , t , j = 7.4 hz , ch3 ) , 1.10 ( 6h , t , j = 7.4 hz , ch3 ) , 1.351.62 ( 16h , m , ch2 ) , 1.701.92 ( 16h , m , ch2 ) , 4.36 ( 4h , t , j = 7.1 hz , och2 ) , 4.42 
 ( 4h , t , j = 6.8 hz , och2 ) , 4.47 ( 4h , t , j = 6.7 hz , och2 ) , 
 4.54 ( 4h , t , j = 6.8 hz , och2 ) , 7.61 ( 2h , s , bn ) , 
 8.86 ( 2h , d , j = 4.8 hz , pyr ) , 9.04 ( 2h , 
 d , j = 1.5 hz , ar ) , 9.08 ( 2h , d , j = 1.5 hz , ar ) , 9.17 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 9.32 ( 2h , d , j = 4.8 hz , pyr ) , 9.46 ( 1h , dd , j1 = j2 = 1.6 hz , ar ) , 
 9.66 ( 2h , s , bn ) , 10.67 ( 2h , s , meso - h ) . c nmr ( cdcl3 )  
 ( ppm ) : 13.67 , 13.74 , 13.80 , 13.84 , 19.16 , 19.18 , 19.27 , 19.32 , 30.63 , 
 30.69 , 30.74 , 65.65 , 65.66 , 65.8 , 66.2 , 102.7 , 115.7 , 120.7 , 121.0 , 
 126.9 , 129.3 , 130.0 , 130.5 , 130.9 , 131.7 , 132.09 , 132.12 , 132.4 , 136.0 , 
 136.7 , 137.2 , 137.3 , 137.8 , 137.9 , 140.3 , 141.50 , 141.52 , 165.2 , 166.0 , 
 166.8 , 168.8 . maldi - tof ( m / z ) : calcd 
 for c80h88n4o16pd 1466.52 , 
 found 1465.90 [ m ] . hrms ( esi - tof ) m / z : [ m + h ] calcd for c80h89n4o16pd 1467.53279 , found 1467.53562 . pt21 was 
 synthesized from 
 pt16 ( 0.04 g , 0.036 mmol ) using ddq ( 0.032 g , 
 0.143 mmol ) . the reaction was complete in 12 h. chromatography was 
 performed using ch2cl2/thf = 5:1 . pt21 was isolated as a pink crystalline powder ( mp > 300 c ) . vis ( dma ) max ( nm ) : 
 405 ( 5.40 ) , 522 ( 4.27 ) , 562 ( 5.03 ) . h nmr ( dmso - d6 , 80 c )  ( ppm ) : 0.99 ( 6h , t , j = 7.3 hz , ch3 ) , 1.491.61 ( 4h , m , ch2 ) , 1.791.90 ( 4h , m , ch2 ) , 4.20 ( 6h , s , och3 ) , 4.21 ( 6h , s , och3 ) , 
 4.51 ( 4h , t , j = 6.5 hz , och2 ) , 7.918.03 ( 2h , m , broad ) , 
 8.098.27 ( 2h , m , broad ) , 8.658.99 ( 10h , m , broad ) . the c nmr spectrum was not recorded because of the low 
 solubility . maldi - tof ( m / z ) : calcd 
 for c52h44n4o12pt 1111.26 , 
 found 1111.72 [ m ] . hrms ( esi - tof ) m / z : [ m ] calcd for c52h44n4o12pt 1111.26014 , found 1111.26239 . pd21 was 
 synthesized from 
 pd16 ( 0.0165 g , 0.016 mmol ) using ddq ( 0.0145 
 g , 0.064 mmol ) . the target porphyrin was purified by column chromatography 
 ( silica gel , ch2cl2/thf = 5:1 ) and then by reprecipitation 
 from thf upon addition of meoh . pd21 was isolated 
 as a dark - purple crystalline powder ( mp > 300 c ) . vis ( dma ) 
 max ( nm ) : 421 , 534 , 574 . h nmr ( dmso - d6 , 80 c )  ( ppm ) : 1.00 ( 6h , t , j = 7.3 hz , ch3 ) , 1.501.61 ( 4h , m , ch2 ) , 1.801.89 ( 4h , m , ch2 ) , 4.124.22 ( 12h , m , och3 ) , 4.50 ( 4h , t , j = 6.5 hz , och2 ) , 7.627.72 
 ( 2h , m , broad ) , 7.737.86 ( 2h , m , broad ) , 8.008.26 
 ( 3h , m , broad ) , 8.298.50 ( 4h , m , broad ) , 8.508.59 
 ( 2h , m , broad ) , 8.858.92 ( 1h , m , broad ) . maldi - tof ( m / z ) : calcd for c52h44n4o12pd 1022.20 , found 1021.71 [ m ] . hrms ( esi - tof ) m / z : [ m ] calcd for c52h44n4o12pd 1022.20031 , found 1022.20218 .