Electrochemical Behavior of meso-Substituted Porphyrins: The Role of Cation Radicals to the Half-Wave Oxidation Potential Splitting

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• 作者：Thai T. H. Tran ; Yan-Ru Chang ; Tuan K. A. Hoang ; Ming-Yu Kuo ; Yuhlong O. Su
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：July 21, 2016
• 年：2016
• 卷：120
• 期：28
• 页码：5504-5511
• 全文大小：517K
• 年卷期：0
• ISSN：1520-5215

文摘

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 E_1/2 – first E_1/2) 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.