Design and characterization of novel A2B2 porphyrins: Solar cell applications, antimicrobial properties, and molecular docking insights

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We synthesized novel A2B2 porphyrin derivatives (5a-e, 7a,b) with yields of 60–73 %. Porphyrin 2 was prepared by reacting dipyrromethane 1 with p-bromobenzaldehyde. Porphyrin 2 was then treated with n-BuLi in DMF at -15 °C to produce porphyrin 3. The final compounds, 5a-e and 7a,b, were synthesized by reacting porphyrin 3 with activated nitriles (4a-e) and thiazolone derivatives (6a,b). The structures of the novel compounds were confirmed using infrared (IR) spectroscopy, proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), mass spectrometry (MS), and elemental analysis. DFT calculations were used to explore the electronic structures and energy levels of the synthesized compounds. Compounds 7a and 7b showed improved electron transfer efficiency compared to 5a-e, with HOMO and LUMO levels aligned for optimal DSSC performance. The HOMO levels are below the electrolyte's redox potential (-5.2 eV), and the LUMO levels are above TiO2's conduction band (-4.2 eV), facilitating efficient electron injection and dye regeneration. Key parameters such as open-circuit voltage (VOC), free energy of injection (ΔGinj), and regeneration (ΔGreg) were calculated, highlighting these compounds' potential for DSSC applications. The newly synthesized compounds were tested for antibacterial activity against C. albicans, B. subtilis, and E. coli. Compounds 5e (MIC50 3.125 µg/mL, with inhibition zone 45 mm against B. subtilis) and (MIC50 12.5 µg/mL, with inhibition zone 31 mm against E. coli) and 7a (MIC50 3.125 µg/mL, with inhibition zone 44 mm against B. subtilis) and (MIC50 12.5 µg/mL, with inhibition zone 30 mm against E. coli) showed the highest antimicrobial activity. Compound 5e's carboxylic acid group likely enhances activity through strong hydrogen bonding and improved solubility, aiding interaction with microbial enzymes or cell walls. Compound 7a's dimalononitrile groups, being highly electron-withdrawing, increase reactivity, while phenylthiazolidine rings offer additional binding sites through hydrogen bonding and pi-stacking interactions. Docking studies of the most potent antibacterial porphyrin analogues, 5e and 7a, against the target protein PDB: 1ECl showed promising results. Compound 5e achieved a docking score of ‐7.9559 kcal/mol with an RMSD of 1.9743 Å, while compound 7a had an even better score of ‐8.9174 kcal/mol. Compound 7a formed interactions with two H-acceptors from its cyano groups, binding to Arg136 and Lys488, and a Pi-H interaction between the thiazolone ring and Asn158, with distances of 3.19, 3.63, and 3.71 Å, respectively.