Unexpected Salt Effects on Charge Separation Yields in Phenothiazine Derivatives-Methylviologen Systems

Article abstract of DOI:10.1021/j100280a115

Neutral salt effects on photoinduced electron-transfer reactions between the singlet excited state of phenothiazine derivatives (PTH) and methylviologen (MV²⁺) were investigated in homogeneous acetyonitrile-water (4/1 v/v) mixture.In the N-methylphenothiazine-MV²⁺ system, the fluorescence quenching reaction was no affected by the addition of neutral salts, whereas the yield of viologen cation radical was greatly improved when some neutral salts having hydrophobic long alkyl chains were added in the solution.The well-known micellar effect was excluded since no preaggregation was found either between salts or between salt and reactant.The increased charge separation yield in the presence of neutral salts was well explained by the suppression of the back-electron-transfer reaction within the geminate ion pair owing to changes in solvation.The effect is discussed with two different and recently developed treatments, (i) solvent fraction and (ii) solvation mode.