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. 2021 Aug 24;6(35):22922–22936. doi: 10.1021/acsomega.1c03534

Large-Scale Green Synthesis of Porphyrins

Sruti Mondal †,‡, Tanmoy Pain †,‡, Kasturi Sahu †,‡, Sanjib Kar †,‡,*
PMCID: PMC8427785  PMID: 34514263

Abstract

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A new methodology for porphyrin synthesis has been developed. This is a simple two-step protocol. The first step involves the condensation of pyrrole and aldehyde in an H2O–MeOH mixture using HCl. The obtained precipitate from the first step was dissolved in reagent-grade dimethylformamide (DMF) and refluxed for 1.5 h, followed by stirring overnight in the air at room temperature. Subsequent purification through column chromatography or crystallization resulted in the formation of pure porphyrins. Advantageously, this methodology does not need any expensive chemicals such as 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), chloranil, and so forth as an oxidizing agent. This reaction also does not require a large volume of dry chlorinated solvents. Contrary to the reported methodologies, which are mostly ineffective in the gram-scale production of porphyrins, the present method perfectly caters to the need for gram-scale production of porphyrins. In essence, the current methodology does not represent the synthesis having the highest yield in the literature. However, it represents the easiest and cheapest synthesis of porphyrin on a large scale to obtain a reproducible yield of 10–40% with high purity. In a few of the examples, even column chromatography is not necessary. A simple crystallization technique will be sufficient to generate the desired porphyrins in good yields.

Introduction

Porphyrin, a natural pigment, is present in a large number of metalloenzymes, such as heme,1 chlorophyll,2 bacteriochlorophyll,3 siroheme,4 heme d1,5 and factor F430.6 Synthetic porphyrinoids and their metallated versions have diverse applications in various areas such as oxidation of organic molecules (as catalysts),7,8 water-splitting reactions (as catalysts),9,10 as possible components in molecular electronics,11 as dyes in dye-sensitized solar cells,12 in supramolecular chemistry,13,14 and also in photodynamic therapy (PDT).15,16 Thus, a great deal of research interest is involved in the synthesis of artificial porphyrin.17−28 Although numerous synthetic procedures have been developed, a careful observation tells us that the choice of reagents and reaction solvents is somewhat limited.29−34 The major obstacle involved in the traditional synthetic pathways is that they are most successful in the small (milligram)-scale synthesis of porphyrin.33,34 An earlier version of porphyrin synthesis by Rothemund et al. describes the synthesis of porphyrin via the reaction of pyrrole and aldehyde in pyridine in a sealed tube at 220 °C.31 However, the reaction yield was as low as 5% in the case of meso-tetraphenylporphyrin.31 Two synthetic methods are nowadays commonly used in porphyrin synthesis.32−34 The Adler–Longo process is a one-step methodology using acetic or propionic acid as a solvent under aerobic conditions at around 141 °C, which results in the formation of the desired porphyrin in 10–30% yield.32 The formation of the tarlike product makes the purification process difficult in many cases. Lindsey’s one-flask two-step methodology was very successful in the synthesis of a large number of porphyrin derivatives (10–60% yield).33,34 One of the major drawbacks of this synthesis is that it normally requires a large amount of chlorinated organic solvents because pyrrole and aldehyde need to be maintained at a very low concentration (∼10 mM) and thus essentially hinders its industrial-scale applications.33,34 In addition to that, in the second step, an expensive oxidizer such as 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) is necessary. This requirement eventually makes this synthetic methodology more costly. From the above discussion, it is clear that an industrial-scale cheap synthesis of porphyrin will have tremendous potential and will eventually make these molecules more relevant for various commercial applications. In the Adler–Longo methodology, pyrrole and benzaldehyde were refluxed in propionic acid, and it resulted in the formation of tetraphenylporphyrin.32 Thus, a direct condensation of pyrrole and benzaldehyde occurs; however, a problem is associated with the generation of different undesired aldehyde–pyrrole oligocondensates. Thus, it lowers the reaction yield and makes the purification of porphyrin quite difficult. Gryko et al. have described the synthesis of tetrapyrrane in high yields in an H2O–CH3OH mixture catalyzed by HCl.35 They have further used tetrapyrrane as a direct precursor of corrole synthesis. Herein, we have observed that tetrapyrrane can be an important intermediate for porphyrin synthesis and will eventually cut down the possibility of the formation of different undesired aldehyde–pyrrole oligocondensates. Thus, it will be easier to obtain the desired porphyrin in high yields without any difficulty in the purification step.

Herein, we have demonstrated a new synthetic protocol for the simplified synthesis of a series of meso-substituted symmetric A4-porphyrins and trans-A2B2-porphyrins under mild conditions (Scheme 1). The first step is the facile condensation of pyrrole/dipyrromethane and aldehyde in a water–methanol solvent mixture using HCl as the catalyst at room temperature (RT). After this reaction, the precipitate is filtered out and dissolved in reagent-grade or ACS-grade dimethylformamide (DMF) and refluxed in the air for 1–2 h. After cooling, it was stirred overnight in the air at RT, dried in a vacuum, and purified by column chromatography. The yield of the obtained porphyrins is mostly satisfactory (10–40%). In a few cases, it is possible to obtain pure porphyrin via a simple crystallization technique, and thus, one can also eliminate the need of column chromatography.

Scheme 1. Synthetic Application of Meso-Substituted Symmetric A4-Porphyrins and Trans-A2B2-Porphyrins.

Scheme 1

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Results and Discussion

A4-Porphyrins: Optimization Study

The acid-catalyzed condensation reaction of pyrrole and aldehyde in the HCl/H2O/MeOH system and the formation of different oligocondensates have already been reported in the literature.35 With a slight modification, the protocol optimized earlier was used here. Following the previous synthetic approach, we have performed the synthesis of tetrapyrrane. For a representative example, 2.0 mmol aldehyde and 2.0 mmol pyrrole were added in a mixture of 100 mL of MeOH and 50 mL of water, followed by 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The resulting mixture was filtered, and the precipitate was collected for the succeeding reaction. It is worth mentioning here that the resulting pink oligocondensates contain a mixture of tetrapyrrane, unreacted aldehyde, and some residual HCl. Gryko et al. extracted this mixture in CHCl3, washed it several times with water, and dried it over Na2SO4. After further dilution in CHCl3, it was oxidized with p-chloranil. This process is now considered as the best protocol for the synthesis of corrole macrocycle.35 While synthesizing A3-corroles, Gryko et al. always observed A4-porphyrins as a side product with an average yield of 1–3%. It was suggested that bilane (tetrapyrrane) scrambling is responsible for this side reaction. This observation indeed promoted us to investigate further the reactivities of tetrapyrrane. Hypothetically, tetrapyrrane can be converted into a porphyrinogen derivative via simple condensation with an aldehyde moiety. A porphyrinogen derivative is considered a direct precursor for porphyrin synthesis. Keeping all these things in mind, we have tried applying the Adler–Longo methodology here. Thus, we took the crude product directly obtained from the HCl/H2O/MeOH system, the pink oligocondensates (tetrapyrrane), and refluxed it with propionic acid. However, this reaction was unsuccessful because of the poor solubility of tetrapyrrane in propionic acid. The resulting mixture was very difficult to purify via column chromatography. We recrystallized it a couple of times but could not obtain any convincing result to proceed further. Our main aim was to replicate the Adler–Longo methodology. Thus, we were looking for an oxidation protocol devoid of quinone-type oxidants such as DDQ or p-chloranil. Thus, we tried with a series of other solvents, specifically alcohols, such as CH3OH, 1-butanol, and so forth. (Table 1). To our surprise, we observed a definitive formation of porphyrin via thin-layer chromatography (TLC). It is indeed possible to separate the generated porphyrin via column chromatography without much difficulty. However, the obtained yield was not satisfactory. While using p-anisaldehyde as the aldehyde, the obtained yield of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin was 4% in CH3OH and 7% in 1-butanol.

Table 1. Optimization of Reaction Conditions for the Conversion of Tetrapyrrane into Porphyrina.

entry solvent porphyrin yielda (%)
1 DMF 29
2 CH3CN 5
3 CH3OH 4
4 Et3N 1–2
5 C5H9NO 14
6 1-butanol 7
7 DCM 10
8 toluene 13
9 propionic acid 0b
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a

5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin, 2.

b

Tetrapyrrane is mostly insoluble in propionic acid.

The change in reflux time does not have any significant effect on the yield of porphyrin. Prolonged reflux eventually decreases the reaction yield further. Using basic solvents such as Et3N also does not improve the situation further. Although porphyrin was formed, the isolated yield was as low as 1–2%. While using other solvents such as dichloromethane (DCM), acetonitrile, and toluene, the yield of porphyrin was also not satisfactory. The obtained yields for the aforementioned solvents were 10, 5, and 13%, respectively. However, when DMF was used as a solvent under the same reaction conditions, our preliminary observation was that porphyrin was formed in a reasonable yield. In this context, we have tried changing the solvent from propionic acid to DMF in the Adler–Longo methodology; however, the reaction remains unsuccessful. The reaction condition in DMF was further optimized by varying the reaction time (Table 2). The initial progress of the reaction was monitored by TLC. The following experiment was carried out using 5,10,15,20-tetraphenylporphyrin as a representative example. When tetrapyrrane was refluxed in DMF for 0.5 h, the desired product was formed in moderate yields. When the reaction was further continued for 0.5 h, there was a slight increase in the yield of the desired porphyrin. The yield of porphyrin further slightly increased by continuing the reaction for another 0.5 h. When the reaction was further continued for 0.5 h, the yield of the desired porphyrin gradually decreased. However, under a similar condition, when the reaction was stirred at room temperature for 1.5 h in the DMF solvent, the desired porphyrin was formed in much lower quantities. Thus, it was observed from the model studies that upon using 5,10,15,20-tetraphenylporphyrin as a representative example, when tetrapyrrane is refluxed in DMF for 1.5 h, the desired porphyrin was formed in satisfactory yields.

Table 2. Optimization of Reaction Conditions for the Conversion of Tetrapyrrane into Porphyrina.

entry temperature time (h) porphyrin yielda (%)
1 RT 1.5 7
2 reflux 0.5 11
3 reflux 1 16
4 reflux 1.5 21
5 reflux 2 17
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a

5,10,15,20-tetraphenylporphyrin, 1.

However, it was further observed that the reaction yield significantly increases upon stirring the same reaction mixture overnight at room temperature. Thus, we can conclude that the optimum yield can be obtained by refluxing the reaction mixture in DMF for 1.5 h, followed by stirring the mixture overnight at RT in air. Overall, we have observed that the reaction yield for 5,10,15,20-tetraphenylporphyrin synthesis is 21%. As N-methyl-2-pyrrolidone (NMP) has properties similar to those of DMF, the reaction was also performed in NMP as the reaction solvent. In the case of the NMP solvent, under similar reaction conditions, the obtained yield for the desired product was 14%. The optimization study was further carried out by varying the solvent from pure DMF to a DMF–water mixed solvent system (Table 3).

Table 3. Optimization of Reaction Conditions for the Conversion of Tetrapyrrane into Porphyrina.

entry solvent porphyrin yielda (%)
1 DMF (dry) 21
2 DMF (HPLC) 21
3 DMF (reagent grade) 21
4 DMF: H2O (4:1) 15
5 DMF: H2O (1:1) 10
6 DMF: H2O (1:4) 6
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a

5,10,15,20-tetraphenylporphyrin, 1.

There was no significant change in the yield of the desired porphyrin upon varying the quality of the solvent. By changing the solvent from dry DMF to HPLC-grade DMF and reagent-grade DMF, the same reaction was performed by following similar optimized reaction conditions, and it was observed that the yield of the porphyrin remains unchanged. Thus, it can be concluded that the yield of porphyrin is not dependent on the purity of the DMF solvent. Therefore, the reaction can be easily carried out in the DMF–water mixed solvent system also. The reaction was performed at varying concentrations of reagent-grade DMF with distilled water to further optimize the reaction conditions. For a representative example, 5,10,15,20-tetraphenylporphyrin, when 20% distilled water was added to 80% reagent-grade DMF, the desired porphyrin was formed in a moderate yield. Upon further diluting the reagent-grade DMF with distilled water (1:1), the desired porphyrin was formed but not in satisfactory yields. When the reagent-grade DMF was further diluted with distilled water (1:4), the yield of the desired porphyrin further decreased.

Aldehydes with varying electronic nature have been tested to synthesize a series of A4-porphyrins; however, it does not change much to the reaction yields. Moderate to good yields of A4-porphyrins are obtained regardless of the electronic nature of the aldehydes (Table 4).

Table 4. Scope of the Synthesis of Meso-Substituted Symmetric A4-Porphyrins.

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To prove the scalability of the process, large-scale synthesis of A4-porphyrins was attempted. For a representative example, 10.0 mmol aldehyde and 10.0 mmol pyrrole were added in a mixture of 500 mL of MeOH and 250 mL of water, followed by 20 mL of HCl. The reaction mixture was stirred at RT for 2 h. The resulting mixture was filtered, and the precipitate was collected. The precipitate was further dissolved in 100 mL of reagent-grade DMF and was refluxed for 1.5 h. After cooling, the reaction mixture was transferred to a beaker and was stirred overnight in the air. Finally, the crude product was purified by column chromatography using silica gel. These scale-up processes furnish similar yields with the small-scale synthesis.

For example, in the case of 5,10,15,20-tetraphenylporphyrin, we have obtained 261 mg (17%) of pure porphyrin, and for 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin, we have obtained 441 mg (24%) of pure porphyrin in gram-scale synthesis. No scrambling was detected via TLC and electrospray ionization-mass spectroscopy (ESI-MS) spectra of the crude reaction mixture. Although tetrapyrrane is a direct precursor for corrole synthesis, we have not obtained any A3-corroles in the reaction mixture in the present case.

Trans-A2B2-Porphyrins: Optimization Study

Trans-A2B2-porphyrins are generally synthesized by following the MacDonald-type [2 + 2] condensation reaction.36 The limitation of this methodology is often the formation of a mixture of different porphyrins rather than the desired porphyrin, which makes the purification process more difficult. Trans-A2B2-porphyrins were synthesized by following the present optimized synthetic methodology. In this present methodology, the purification of the desired porphyrin is rather convenient. For the synthesis of various trans-A2B2-porphyrins, dipyrromethanes were used instead of pyrrole (Table 5). Dipyrromethanes are usually synthesized by reacting an aldehyde with pyrrole in the presence of trifluoroacetic acid. In a typical procedure, 1.0 mmol aldehyde and 1.0 mmol dipyrromethane were added to a mixture of 100 mL of MeOH and 50 mL of water, followed by 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The resulting mixture was filtered, and the precipitate was collected for the succeeding reaction. The precipitate was further dissolved in a minimum quantity of reagent-grade DMF and was refluxed for 1.5 h. After cooling, the reaction mixture was transferred to a beaker and was stirred overnight in the air. Finally, the crude product was purified by column chromatography using silica gel for some cases. Also, for the rest of the cases, the desired porphyrin precipitated out from the solution. The crystals of the desired porphyrin can be easily collected by filtration and purified by washing the precipitate with MeOH. Dipyrromethanes with varying electron-withdrawing and electron-releasing groups were tested for the synthesis of a series of trans-A2B2-porphyrins; however, no clear-cut electronic effect was observed. Moderate to good yields of trans-A2B2-porphyrins were obtained regardless of the electronic structure of dipyrromethanes. No scrambling was detected via TLC and ESI-MS spectra of the crude reaction mixture. The mechanism of the reaction can be assigned based on the Adler–Longo methodology of porphyrin synthesis. The tetrapyrrane derivative, the unreacted aldehyde, and some residual HCl obtained from the first step were possibly converted into a porphyrinogen derivative in the DMF solvent and were further oxidized by aerial O2, and the desired porphyrin was generated.

Table 5. Scope of the Synthesis of Meso-Substituted Trans-A2B2-Porphyrins.

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Analysis of the Reaction Mechanism

Based on these observations, we can postulate the probable mechanism for the porphyrin synthesis (Figure 1). The first step involves a simple condensation reaction between pyrrole/dipyrromethane using a suitable aldehyde in a water–methanol mixture via HCl catalysis and the generation of the corresponding tetrapyrranes. Earlier studies have well documented this step.35 In the subsequent step, the coupling of tetrapyrranes with a suitable aldehyde is imminent, and aerobic oxidation is responsible for the generation of corresponding porphyrin derivatives.32

Figure 1.

Figure 1

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Proposed mechanism.

Conclusions

The synthesis of symmetric A4-porphyrins from aromatic aldehydes that possess a variety of substituents exhibiting the highest yield of 29% and the [2 + 2] synthesis of trans-A2B2-porphyrins from dipyrromethanes bearing different substituents exhibiting the highest yield of 40% are reported herein. The first step involves the HCl-catalyzed condensation reaction of pyrrole and aldehyde in an H2O–MeOH mixture. In the subsequent step, the obtained precipitate was dissolved in reagent-grade DMF, refluxed (1–2 h), and stirred overnight in the air at RT, followed by purification via column chromatography/crystallization, which resulted in the formation of pure porphyrins. The conditions described in this study provide the easiest and cheapest synthesis of porphyrin on a large scale for obtaining a reproducible yield of 10–40% with high purity. The synthesis of trans-A2B2-porphyrins from dipyrromethanes is also free of scrambling. Advantageously, this methodology does not need any expensive traditional oxidizers such as DDQ, chloranil, and so forth. This reaction also does not need a large volume of dry chlorinated solvents. Thus, the present synthetic approach can open up an avenue for the synthesis of a wide range of symmetric-A4 and trans-A2B2-porphyrins on a large scale, which will further widen the practical applications of these important classes of molecules. In essence, the present methodology does not represent the synthesis that exhibits the highest yield in the literature; however, it does represent the easiest and cheapest synthesis of porphyrin on a large scale for obtaining a reproducible yield of 10–40% with high purity.

Experimental Section

Materials

The precursor’s pyrrole and aldehydes were purchased from Aldrich, USA. DMF was purchased from Merck Pvt. Ltd chemicals. Other chemicals were of reagent grade. Hexane, CH2Cl2, and CH3CN were distilled from KOH and CaH2. For spectroscopy studies, HPLC-grade solvents were used. 5-phenyldipyrromethane, 5-(4-methoxyphenyl)dipyrromethane, 5-(4-bromophenyl)dipyrromethane, and 5-(4-cyanophenyl)dipyrromethane were prepared by following the procedure reported earlier.35

Physical Measurements

The elemental analyses were carried out with a Euro EA elemental analyzer. Ultraviolet–visible (UV–vis) spectral studies were performed on a Perkin-Elmer LAMBDA-750 spectrophotometer. Emission spectral studies were performed on a Perkin Elmer LS 55 spectrophotometer using an optical cell of 1 cm path length. Nuclear magnetic resonance (NMR) measurements were carried out using a Bruker 400 MHz NMR spectrometer. Chemical shifts are expressed in parts per million (ppm) relative to residual solvents. Electrospray mass spectra were recorded on a Bruker Micro TOF-QII mass spectrometer.

Experimental Section

Synthesis of 5,10,15,20-Tetraphenylporphyrin, 1

Benzaldehyde (204 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,10,15,20-Tetraphenylporphyrin, 1

Yield: 21% (61 mg). Anal. Calcd (found) for C44H30N4 (1): C, 85.97 (85.88); H, 4.92 (4.83); N, 9.11 (9.17). 1H NMR (400 MHz, chloroform-d) δ 8.85 (s, 8H), 8.25–8.19 (m, 8H), 7.79–7.72 (m, 12H), −2.78 (s, 2H) (Figure S1). Other analytical data are consistent with those of the previously reported authentic compounds.37

Gram-Scale Synthesis of 5,10,15,20-Tetraphenylporphyrin, 1

Benzaldehyde (1.02 mL) (10 mmol) and 694 μL (10 mmol) of pyrrole were added to a mixture of 500 mL of MeOH and 250 mL of water (2:1), followed by the addition of 20 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 100 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh), or it can be purified via crystallization also. Yield: 17% (261 mg).

Synthesis of 5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin, 2

4-Methoxybenzaldehyde (243 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin, 2

Yield: 29% (105 mg). Anal. Calcd (found) for C48H38N4O4 (2): C, 78.45 (78.55); H, 5.21 (5.32); N, 7.62 (7.77). 1H NMR (400 MHz, chloroform-d) δ 8.86 (s, 8H), 8.13 (d, J = 8.0 Hz, 8H), 7.29 (d, J = 8.0 Hz, 8H), 4.10 (s, 12H), −2.75 (s, 2H) (Figure S2). Other analytical data are consistent with those of the previously reported authentic compounds.37

Gram-Scale Synthesis of 5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin, 2

4-Methoxybenzaldehyde (1.2 mL) (10 mmol) and 694 μL (10 mmol) of pyrrole were added to a mixture of 500 mL of MeOH and 250 mL of water (2:1), followed by the addition of 20 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 100 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization. Yield: 24% (441 mg).

Synthesis of 5,10,15,20-Tetrakis(4-nitrophenyl)porphyrin, 3

4-Nitrobenzaldehyde (302 mg) (2 mmol) and 140 μL of (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,10,15,20-Tetrakis(4-nitrophenyl)porphyrin, 3

Yield: 28% (109 mg). Anal. Calcd (found) for C44H26N8O8 (3): C, 66.50 (66.62); H, 3.30 (3.39); N, 14.10 (14.01). 1H NMR (400 MHz, chloroform-d) δ 8.82 (m, 8H), 8.68 (m, 8H), 8.40 (m, 8H), −2.82 (s, 2H) (Figure S3). m/z: [3 + H]+ Calcd for C44H27N8O8 795.1946; Found 795.1983 (Figure S31). Other analytical data are consistent with those of the previously reported authentic compounds.38

Synthesis of 5,10,15,20-Tetrakis(4-chlorophenyl)porphyrin, 4

4-Chlorobenzaldehyde (281 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4-chlorophenyl)porphyrin, 4

Yield: 20% (76 mg). Anal. Calcd (found) for C44H26Cl4N4 (4): C, 70.23 (70.13); H, 3.48 (3.38); N, 7.45 (7.58). 1H NMR (400 MHz, chloroform-d) δ 8.84 (s, 8H), 8.16–8.12 (d, 8H), 7.78–7.72 (d, 8H), −2.85 (s, 2H) (Figure S4). Other analytical data are consistent with those of the previously reported authentic compounds.39

Synthesis of 5,10,15,20-Tetrakis(4-methylphenyl)porphyrin, 5

p-Tolualdehyde (236 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,10,15,20-Tetrakis(4-methylphenyl)porphyrin, 5

Yield: 20% (66 mg). Anal. Calcd (found) for C48H38N4 (5): C, 85.94 (85.85); H, 5.71 (5.62); N, 8.35 (8.47). 1H NMR (400 MHz, chloroform-d) δ 8.85 (s, 8H), 8.12–8.08 (m, 8H), 7.55 (d, J = 7.7 Hz, 8H), 2.71 (s, 12H), −2.77 (s, 2H) (Figure S5). Other analytical data are consistent with those of the previously reported authentic compounds.39

Synthesis of 5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)porphyrin, 6

2,4,6-Trimethylbenzaldehyde (296 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)porphyrin, 6

Yield: 20% (78 mg). Anal. Calcd (found) for C56H54N4 (6): C, 85.89 (85.78); H, 6.95 (6.87); N, 7.15 (7.27). 1H NMR (400 MHz, chloroform-d) δ 8.62 (s, 8H), 7.26 (s, 8H), 2.62 (s, 12H), 1.85 (s, 24H), −2.50 (s, 2H) (Figure S6). Other analytical data are consistent with those of the previously reported authentic compounds.40

Synthesis of 5,10,15,20-Tetrakis(4-ethylphenyl)porphyrin, 7

4-Ethylbenzaldehye (268 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,10,15,20-Tetrakis(4-ethylphenyl)porphyrin, 7

Yield: 17% (60 mg). Anal. Calcd (found) for C52H46N4 (7): C, 85.91 (85.98); H, 6.38 (6.33); N, 7.71 (7.62). 1H NMR (400 MHz, chloroform-d) δ 8.88 (s, 8H), 8.18–8.10 (d, J = 7.9 Hz, 8H), 7.58 (d, J = 7.9 Hz, 8H), 3.02 (q, J = 7.6 Hz, 8H), 1.55–1.51 (m, 12H), −2.73 (s, 2H) (Figure S7). Other analytical data are consistent with those of the previously reported authentic compounds.41

Synthesis of 5,10,15,20-Tetrakis(4-cyanophenyl)porphyrin, 8

4-Cyanobenzaldehyde (262 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4-cyanophenyl)porphyrin, 8

Yield: 12% (44 mg). Anal. Calcd (found) for C48H26N8 (5): C, 80.66 (80.50); H, 3.67 (3.53); N, 15.68 (15.77). 1H NMR (400 MHz, chloroform-d) δ 8.80 (s, 8H), 8.33 (d, J = 7.8 Hz, 8H), 8.10 (d, J = 7.9 Hz, 8H), −2.88 (s, 2H) (Figure S8). Other analytical data are consistent with those of the previously reported authentic compounds.38

Synthesis of 5,10,15,20-Tetrakis(4-iodophenyl)porphyrin, 9

4-Iodobenzaldehyde (464 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4-iodophenyl)porphyrin, 9

Yield: 12% (63 mg). Anal. Calcd (found) for C44H26I4N4 (9): C, 47.26 (47.39); H, 2.34 (2.43); N, 5.01 (5.17). 1H NMR (400 MHz, chloroform-d) δ 8.84 (s, 8H), 8.11 (d, J = 8.0 Hz, 8H), 7.93 (d, J = 8.0 Hz, 8H), −2.88 (s, 2H) (Figure S9). Other analytical data are consistent with those of the previously reported authentic compounds.42

Synthesis of 5,10,15,20-Tetrakis(4-bromophenyl)porphyrin, 10

4-Bromobenzaldehyde (370 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4-bromophenyl)porphyrin, 10

Yield: 9% (40 mg). Anal. Calcd (found) for C44H26Br4N4 (10): C, 56.81 (56.95); H, 2.82 (2.93); N, 6.02 (6.17). 1H NMR (400 MHz, chloroform-d) δ 8.84 (s, 8H), 8.07 (d, J = 8.1 Hz, 8H), 7.90 (dd, J = 8.2, 1.4 Hz, 8H), −2.87 (s, 2H) (Figure S10). Other analytical data are consistent with those of the previously reported authentic compounds.43

Synthesis of 5,10,15,20-Tetrakis(3-Bromophenyl)Porphyrin, 11

3-Bromobenzaldehyde (233 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(3-bromophenyl)porphyrin, 11

Yield: 7% (30 mg). Anal. Calcd (found) for C44H26Br4N4 (11): C, 56.81 (56.70); H, 2.82 (2.73); N, 6.02 (6.14). 1H NMR (400 MHz, chloroform-d) δ 8.86 (s, 8H), 8.38 (s, 4H), 8.15 (d, J = 7.5 Hz, 4H), 7.95 (d, J = 8.1 Hz, 4H), 7.64 (t, J = 7.9 Hz, 4H), −2.89 (s, 2H) (Figure S11). Other analytical data are consistent with those of the previously reported authentic compounds.44

Synthesis of 5,10,15,20-(Tetra-4-trifluoromethylphenyl)porphyrin, 12

4-(Trifluoromethyl)benzaldehyde (273 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-(Tetra-4-trifluoromethylphenyl)porphyrin, 12

Yield: 4% (15 mg). Anal. Calcd (found) for C48H26F12N4 (12): C, 65.02 (64.91); H, 2.96 (2.85); N, 6.32 (6.21). 1H NMR (400 MHz, chloroform-d) δ 8.81 (s, 8H), 8.34 (d, J = 7.9 Hz, 8H), 8.05 (d, J = 8.0 Hz, 8H), −2.83 (s, 2H) (Figure S12). Other analytical data are consistent with those of the previously reported authentic compounds.45

Synthesis of 5,10,15,20-Tetrakis(4-butoxyphenyl)porphyrin, 13

4-(tert-butyloxy)benzaldehyde (348 μL) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water, followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4-butoxyphenyl)porphyrin, 13

Yield: 12% (51 mg). Anal. Calcd (found) for C60H62N4O4 (13): C, 79.79 (79.68); H, 6.92 (6.99); N, 6.20 (6.13). 1H NMR (400 MHz, chloroform-d) δ 8.87 (s, 8H), 8.15–8.04 (d, 8H), 7.40–7.36 (m, 8H), 1.62 (s, 36H), −2.75 (s, 2H) (Figure S13). Other analytical data are consistent with those of the previously reported authentic compounds.38

Synthesis of 5,10,15,20-Tetrakis[4-(benzyloxy)phenyl]porphyrin, 14

4-(Benzyloxy)benzaldehyde (424 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis[4-(benzyloxy)phenyl]porphyrin, 14

Yield: 16% (80 mg). Anal. Calcd (found) for C72H54N4O4 (14): C, 83.21 (83.16); H, 5.24 (5.32); N, 5.39 (5.48). 1H NMR (400 MHz, methylene chloride-d2) δ 8.90 (s, 8H), 8.14 (d, J = 8.1 Hz, 8H), 7.65 (d, J = 7.4 Hz, 8H), 7.51 (t, J = 7.5 Hz, 8H), 7.41 (m, 12H), 5.37 (s, 8H), −2.81 (s, 2H) (Figure S14). Other analytical data are consistent with those of the previously reported authentic compounds.46

Synthesis of 5,10,15,20-Tetrakis(4-methoxycarbonylphenyl)porphyrin, 15

Methyl 4-formylbenzoate (328 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4-methoxycarbonylphenyl)porphyrin, 15

Yield: 10% (39 mg). Anal. Calcd (found) for C52H38N4O8 (15): C, 73.75 (73.65); H, 4.52 (4.63); N, 6.62 (6.77). 1H NMR (400 MHz, chloroform-d) δ 8.82 (s, 8H), 8.47–8.43 (d, 8H), 8.32–8.27 (d, 8H), 4.11 (s, 12H), −2.81 (s, 2H) (Figure S15). Other analytical data are consistent with those of the previously reported authentic compounds.47

Synthesis of 5,10,15,20-Tetrakis(4,7 – dimethoxynaphthalen-1-yl)porphyrin, 16

4,7-Dimethoxy-1-naphthaldehyde (432 mg) (2 mmol) and 140 μL (2 mmol) of pyrrole were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,10,15,20-Tetrakis(4,7 – dimethoxynaphthalen-1-yl)porphyrin, 16

Yield: 17% (89 mg). Anal. Calcd (found) for C68H54N4O8 (16): C, 77.40 (77.52); H, 5.16 (5.30); N, 5.31 (5.18). 1H NMR (400 MHz, chloroform-d) δ 8.58 (d, J = 5.7 Hz, 8H), 8.44 (td, J = 7.0, 3.4 Hz, 4H), 8.08–7.99 (m, 4H), 7.17–7.03 (m, 8H), 6.60 (dd, J = 22.7, 2.5 Hz, 2H), 6.55–6.45 (m, 2H), 4.23 (d, J = 2.0 Hz, 12H), 3.00–2.89 (m, 12H), −2.27 (s, 2H) (Figure S16). 13C {1H} NMR (101 MHz, CDCl3) δ 161.4, 158.5, 158.5, 156.2, 151.6, 139.6, 139.0, 134.2, 130.5, 129.0, 128.9, 123.7, 120.2, 120.2, 118.8, 118.0, 117.4, 107.6, 107.4, 105.6, 104.8, 103.1, 101.8, 101.1, 101.0, 55.9, 55.0, 54.9, 54.8, 54.7 (Figure S17). m/z: [16 + H]+ Calcd for C68H55N4O8 1055.4014; Found 1055.3948 (Figure S32).

Synthesis of 5,15-Bis(4-bromophenyl)- 10,20-bis(4-nitrophenyl)porphyrin, 21

5-(4-Bromophenyl)dipyrromethane (301 mg) (1 mmol) and 151 mg (1 mmol) of 4-nitrobenzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,15-Bis(4-bromophenyl)- 10,20-bis(4-nitrophenyl)porphyrin, 21

Yield: 40% (170 mg). Anal. Calcd (found) for C44H26Br2N6O4 (21): C, 61.27 (61.38); H, 3.04 (3.17); N, 9.74 (9.87). 1H NMR (400 MHz, chloroform-d) δ 8.89 (d, J = 4.8 Hz, 4H), 8.78 (d, J = 4.9 Hz, 4H), 8.68–8.64 (m, 4H), 8.41–8.37 (m, 4H), 8.09–8.05 (m, 4H), 7.95–7.91 (m, 4H), −2.86 (s, 2H) (Figure S18). Other analytical data are consistent with those of the previously reported authentic compounds.48

Synthesis of 5,15-Bis(4-nitrophenyl)-10,20-diphenylporphyrin, 22

5-Phenyldipyrromethane (222 mg) (1 mmol) and 151 mg (1 mmol) of 4-nitrobenzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,15-Bis(4-nitrophenyl)-10,20-diphenylporphyrin, 22

Yield: 31% (108 mg). Anal. Calcd (found) for C44H28N6O4 (22): C, 74.99 (75.11); H, 4.00 (4.16); N, 11.93 (11.82). 1H NMR (400 MHz, chloroform-d) δ 8.91 (d, J = 4.8 Hz, 4H), 8.76 (d, J = 4.8 Hz, 4H), 8.65 (d, J = 8.3 Hz, 4H), 8.40 (d, J = 8.3 Hz, 4H), 8.21 (d, J = 7.0 Hz, 4H), 7.79 (m, 6H), −2.79 (s, 2H) (Figure S19). Other analytical data are consistent with those of the previously reported authentic compounds.48

Synthesis of 5,15-Bis(4-methoxyphenyl)-10,20-bis(4-nitrophenyl)porphyrin, 23

5-(4-Methoxyphenyl)dipyrromethane (252 mg) (1 mmol) and 151 mg (1 mmol) of 4-nitrobenzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,15-Bis(4-methoxyphenyl)-10,20-bis(4-nitrophenyl)porphyrin, 23

Yield: 30% (114 mg). Anal. Calcd (found) for C46H32N6O6 (23): C, 72.24 (72.13); H, 4.22 (4.10); N, 10.99 (11.14). 1H NMR (400 MHz, chloroform-d) δ 8.94 (d, J = 4.8 Hz, 4H), 8.74 (d, J = 4.8 Hz, 4H), 8.66–8.61 (m, 4H), 8.39 (d, J = 8.3 Hz, 4H), 8.14–8.09 (m, 4H), 7.34–7.29 (m, 4H), 4.10 (s, 6H), −2.77 (s, 2H) (Figure S20). Other analytical data are consistent with those of the previously reported authentic compounds.49

Synthesis of 5,15-bis(4-cyanophenyl)-10,20-bis(4-nitrophenyl)porphyrin, 24

5-(4-Cyanophenyl)dipyrromethane (247 mg) (1 mmol)and 151 mg (1 mmol) of 4-nitrobenzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,15-bis(4-cyanophenyl)-10,20-bis(4-nitrophenyl)porphyrin, 24

Yield: 23% (85 mg). Anal. Calcd (found) for C46H26N8O4 (24): C, 73.20 (73.34); H, 3.47 (3.31); N, 14.85 (14.73). 1H NMR (400 MHz, chloroform-d) δ 8.81 (s, 8H), 8.67 (d, J = 8.2 Hz, 4H), 8.39 (d, J = 8.4 Hz, 4H), 8.34 (d, J = 7.8 Hz, 4H), 8.10 (d, J = 7.7 Hz, 4H), −2.85 (s, 2H) (Figure S21). 13C {1H} NMR (101 MHz, CDCl3) δ 167.9, 143.4, 142.0, 138.3, 135.3, 135.1, 132.6, 131.0, 130.8, 128.9, 128.4, 122.2, 121.7, 112.5, 111.3, 109.5, 107.1, 103.0, 96.7 (Figure S22). m/z: [24 + H]+ Calcd for C46H27N8O4 755.2150; Found 755.2081 (Figure S33).

Synthesis of 5,15-Bis(4-methoxyphenyl)-10,20-(4-chlorophenyl)porphyrin, 25

5-(4-Methoxyphenyl)dipyrromethane (252 mg) (1 mmol) and 141 mg (1 mmol) of 4-chlorobenzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-Bis(4-methoxyphenyl)-10,20-(4-chlorophenyl)porphyrin, 25

Yield: 19% (69 mg). Anal. Calcd (found) for C46H32Cl2N4O2 (25): C, 74.29 (74.42); H, 4.34 (4.45); N, 7.53 (7.67). 1H NMR (400 MHz, chloroform-d) δ 8.91–8.79 (m, 8H), 8.18–8.10 (m, 8H), 7.76–7.71 (m, 4H), 7.30 (d, J = 8.2 Hz, 4H), 4.10 (s, 6H), −2.79 (s, 2H) (Figure S23). Other analytical data are consistent with those of the previously reported authentic compounds.50

Synthesis of 5,15-Bis(4-cyanophenyl)-10,20-diphenylporphyrin, 26

5-(4-Cyanophenyl)dipyrromethene (247 mg) (1 mmol) and 102 μL (1 mmol) of benzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-Bis(4-cyanophenyl)-10,20-diphenylporphyrin, 26

Yield: 17% (57 mg). Anal. Calcd (found) for C46H28N6 (26): C, 83.11 (83.02); H, 4.25 (4.37); N, 12.64 (12.52). 1H NMR (400 MHz, chloroform-d) δ 8.90 (d, J = 4.8 Hz, 4H), 8.75 (d, J = 4.8 Hz, 4H), 8.37–8.31 (d, 4H), 8.23–8.17 (d, 4H), 8.10–8.05 (d, 4H), 7.79 (m, 6H), −2.83 (s, 2H) (Figure S24). Other analytical data are consistent with those of the previously reported authentic compounds.37

Synthesis of 5,15-Bis(4-bromophenyl)-10,20-(4-methylphenyl)porphyrin, 27

5-(4-Bromophenyl)dipyrromethane (301 mg) (1 mmol) and 117 μL (1 mmol) of p-tolualdehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-Bis(4-bromophenyl)-10,20-(4-methylphenyl)porphyrin, 27

Yield: 13% (51 mg). Anal. Calcd (found) for C46H32Br2N4 (27): C, 69.01 (69.14); H, 4.03 (4.17); N, 7.00 (6.88). 1H NMR (400 MHz, chloroform-d) δ 8.85 (dd, J = 32.6, 4.8 Hz, 8H), 8.08 (m, 8H), 7.91–7.87 (m, 4H), 7.56 (d, J = 7.6 Hz, 4H), 2.71 (s, 6H), −2.80 (s, 2H) (Figure S25). Other analytical data are consistent with those of the previously reported authentic compounds.51

Synthesis of 5,15-bis(4-cyanophenyl)-10,20-bis(4-methoxyphenyl)porphyrin, 28

5-(4-Cyanophenyl)dipyrromethene (247 mg) (1 mmol) and 122 μL (1 mmol) of 4-methoxybenzaldehyde were added to a mixture of 100 of mL MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-bis(4-cyanophenyl)-10,20-bis(4-methoxyphenyl)porphyrin, 28

Yield: 13% (45 mg). Anal. Calcd (found) for C48H32N6O2 (28): C, 79.54 (79.46); H, 4.45 (4.56); N, 11.59 (11.67). 1H NMR (400 MHz, chloroform-d) δ 8.92 (d, J = 4.8 Hz, 4H), 8.73 (d, J = 4.8 Hz, 4H), 8.34 (d, J = 7.8 Hz, 4H), 8.09 (m, 8H), 7.31 (d, J = 8.2 Hz, 4H), 4.11 (s, 6H), −2.80 (s, 2H) (Figure S26). Other analytical data are consistent with those of the previously reported authentic compounds.37

Synthesis of 5,15-bis(4-methylphenyl)-10,20-diphenylporphyrin, 29

5-Phenyldipyrromethane (222 mg) (1 mmol) and 117 μL (1 mmol) of p-tolualdehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-bis(4-methylphenyl)-10,20-diphenylporphyrin, 29

Yield: 11% (34 mg). Anal. Calcd (found) for C46H34N4 (29): C, 85.95 (85.81); H, 5.33 (5.43); N, 8.72 (8.64). 1H NMR (400 MHz, chloroform-d) δ 8.89–8.82 (m, 8H), 8.24–8.20 (m, 4H), 8.12–8.09 (m, 4H), 7.79–7.74 (m, 6H), 7.56 (d, J = 7.7 Hz, 4H), 2.71 (s, 6H), −2.77 (s, 2H) (Figure S27). Other analytical data are consistent with those of the previously reported authentic compounds.52

Synthesis of 5,15-bis(4-methoxyphenyl)-10,20-(4-methylphenyl)porphyrin, 30

5-(4-Methoxyphenyl)dipyrromethane (252 mg) (1 mmol) and 117 μL (1 mmol) of p-tolualdehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh) or purified via crystallization.

For 5,15-bis(4-methoxyphenyl)-10,20-(4-methylphenyl)porphyrin, 30

Yield: 9% (30 mg). Anal. Calcd (found) for C48H38N4O2 (30): C, 82.03 (82.14); H, 5.45 (5.34); N, 7.97 (7.88). 1H NMR (400 MHz, chloroform-d) δ 8.85 (s, 8H), 8.11 (m, 8H), 7.55 (d, J = 7.6 Hz, 4H), 7.29 (d, J = 8.5 Hz, 4H), 4.10 (s, 6H), 2.71 (s, 6H), −2.76 (s, 2H) (Figure S28). Other analytical data are consistent with those of the previously reported authentic compounds.52

Synthesis of 5,15-bis(4-methoxyphenyl)-10,20-diphenylporphyrin, 31

5-(4-Methoxyphenyl)dipyrromethane (252 mg) (1 mmol) and 102 μL (1 mmol) of benzaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-bis(4-methoxyphenyl)-10,20-diphenylporphyrin, 31

Yield: 9% (31 mg). Anal. Calcd (found) for C46H34N4O2 (31): C, 81.88 (81.99); H, 5.08 (4.97); N, 8.30 (8.45). 1H NMR (400 MHz, chloroform-d) δ 8.91–8.82 (m, 8H), 8.24–8.20 (m, 4H), 8.16–8.11 (m, 4H), 7.77 (m, 6H), 7.31–7.27 (m, 4H), 4.10 (s, 6H), −2.76 (s, 2H) (Figure S29). Other analytical data are consistent with those of the previously reported authentic compounds.52

Synthesis of 5,15-bis(4-cyanophenyl)-10,20-bis(2,4,6-trimethylphenyl)porphyrin, 32

5-(4-Cyanophenyl)dipyrromethene (247 mg) (1 mmol) and 148 μL (1 mmol) of mesitaldehyde were added to a mixture of 100 mL of MeOH and 50 mL of water (2:1), followed by the addition of 10 mL of HCl. The reaction mixture was stirred at RT for 2 h. The reaction mixture was filtered with Whatman filter paper, and the precipitate was dissolved in 15 mL of DMF solution. This DMF solution was refluxed for another 1.5 h. This solution was finally transferred to a beaker and was stirred overnight. Then, the solution was evaporated to dryness. The crude product was purified by column chromatography using silica gel (100–200 mesh).

For 5,15-bis(4-cyanophenyl)-10,20-bis(2,4,6-trimethylphenyl)porphyrin, 32

Yield: 5% (20 mg). Anal. Calcd (found) for C52H40N6 (32): C, 83.39 (83.27); H, 5.38 (5.26); N, 11.22 (11.31). 1H NMR (400 MHz, chloroform-d) δ 8.74 (d, J = 4.8 Hz, 4H), 8.69 (d, J = 4.8 Hz, 4H), 8.35 (d, J = 8.0 Hz, 4H), 8.06 (d, J = 8.1 Hz, 4H), 7.29 (s, 4H), 2.63 (s, 6H), 1.82 (s, 12H), −2.68 (s, 2H) (Figure S30). Other analytical data are consistent with those of the previously reported authentic compounds.53

Acknowledgments

Financial support received from the Department of Atomic Energy, India, is gratefully acknowledged. Authors thankfully acknowledge NISER-Bhubaneswar for providing infrastructure. The authors gratefully acknowledge the financial support provided by SERB (Science and Engineering Research Board), India (EMR/2016/005484), to carry out this work. K.S. thanks CSIR India for research fellowship.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c03534.

  • 1H-NMR, 13C-NMR, and ESI-MS data of the synthesized compounds (1–32) (PDF).

The authors declare no competing financial interest.

This paper was published ASAP on August 24, 2021, with a compound in Table 4 incorrectly formatted during production. The corrected version was posted on August 25, 2021.

Supplementary Material

ao1c03534_si_001.pdf (1.3MB, pdf)

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