Coulombic Effect on Photoinduced Electron-Transfer Reactions between Phenothiazines and Viologens

Article abstract of DOI:10.1021/j100402a041

Photoinduced electron-transfer reactions between excited phenothiazine derivatives (PTH) and viologens (V) were investigated in aqueous acetonitrile at room temperature.Ionic substituents on PTH or V strongly affected the reaction kinetics, and the Coulombic effects on the reactions were interpreted by the work terms w_r and w_p, where r and p represent reactants and products, respectively.Fluorescence quenching reactions proceeded with the diffusion-controlled rate constants which were dependent on w_r and were explained by the Debye-Smoluchowski equation.Charge separation efficiency (F) corresponding to the cage escape yield of geminate ion radical pair strongly depended on (w_p - w_r), which indicated that (i) the back-electron-transfer rate determined F and (ii) the Coulombic work terms decided the back-electron-transfer rate.Quantitative teatments of the present results demonstrated that Coulombic effects can be used effectively to generate highly efficient photoredox systems.