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In this study, the electrochemical behavior of free base and zinc meso-substituted porphyrins is examined by cyclic voltammetry (CV) and density functional theory (DFT). The results show that the half-wave oxidation potential splitting of the two oxidation states (ΔE= second E1/2 - first E1/2) of tetraphenylporphyrin (H2TPP) and its zinc complex (ZnTPP) are higher than those of porphyrins and their zinc complexes with meso-substituted five-membered heterocylic rings. The ΔE values follow the trend of TPP > T(3'-thienyl)P > T(3'-furyl)P > T(2'-thienyl)P for both meso-porphyrins and their respective zinc complexes. By employing DFT calculations, we have found that the trend of ΔE values is consistent with that of highest spin density (HSD) distribution and HOMO-LUMO energy gaps of cationic radicals as well as the π-conjugation between central porphyrin and meso-substituted rings. Also, they exhibit the better resonance between the porphyrin ring with meso-substituted rings as moving from porphyrins and their zinc complexes with phenyl rings to five-membered heterocyclic rings. A good agreement between calculated and experimental results indicates that cationic radicals, especially their spin density distribution, do play an important role in half-wave oxidation potential splitting of meso-porphyrins and their zinc complexes.

By nature of their nucleophilicity, all thiol-based drugs are oxidatively metabolized in the physiological environment. The key to understanding the physiological role of a hypertension drug, (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid, medically known as captopril is through studying its oxidation pathway: its reactive intermediates and oxidation products. The oxidation of captopril by aqueous bromine and acidified bromate has been studied by spectrophotometric and electrospray ionization techniques. The stoichiometry for the reaction of acidic bromate with captopril is 1:1, BrO3(-) + (C4H6N)(COOH)(COCHCH3CH2)-SH → (C4H6N)(COOH)(COCHCH3CH2)-SO3H + Br(-), with reaction occurring only at the thiol center. For the direct reaction of bromine with captopril, the ratio is 3:1; 3Br2 + (C4H6N)(COOH)(COCHCH3CH2)-SH + 3H2O → (C4H6N)(COOH)(COCHCH3CH2)-SO3H + 6HBr. In excess acidic bromate conditions the reaction displays an initial induction period followed by a sharp rise in absorbance at 390 nm due to rapid formation of bromine. The direct reaction of aqueous bromine with captopril was much faster than oxidation of the thiol by acidified bromate, with a bimolecular rate constant of (1.046 (±0.08) × 10(5) M(-1) s(-1). The detection of thiyl radicals confirms the involvement of radicals as intermediates in the oxidation of Captopril by acidified BrO3(-). The involvement of thiyl radicals in oxidation of captopril competes with a nonradical pathway involving 2-electron oxidations of the sulfur center. The oxidation product of captopril under these strong oxidizing conditions is a sulfonic acid as confirmed by electrospray ionization mass spectrometry (ESI-MS), iodometric titrations, and proton nuclear magnetic resonance ((1)H NMR) results. There was no evidence from ESI-MS for the formation of the sulfenic and sulfinic acids in the oxidation pathway as the thiol group is rapidly oxidized to the sulfonic acid. A computer simulation analysis of this mechanism gave a reasonably good fit to the experimental data.

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A series of novel sensitizers were successfully synthesized utilizing azobenzene as a π‐linkage unit for the D–π–A structure. A slight red shift on the absorption spectra and λonset of the sensitizers could be observed when the thienyl group was introduced to the acceptor moiety (A). In addition, replacing the donor moiety (D) from carbazole to diarylamino could lead to a negative shift (approximately 0.3 V) in the first oxidation potential. DFT calculation was also carried out and the trend of calculated HOMO–LUMO gaps was consistent to the experimental data obtained from the CV results (DT1 < DT2 < DT3 < DT4). These sensitizers were then employed in dye‐sensitized solar cells to investigate their photovoltaic performances. Highest power conversion efficiency (PCE) of 0.84% was achieved for DT1‐based DSSC according to its most bathochromic absorption spectrum.