Solvent effects on intermolecular photoinduced electron transfer reactions of aromatic molecules

The electron transfer quenching of excited singlet of pyrene by indole and 3-cyanopyridine, and a,h-dibenzanthracene by o-dicyanobenzene was investigated in solvents of different polarity. The electron transfer nature of the quenching reaction in all the solvents was confirmed by the transient absorption spectra of the radical ions formed. Quenching rate constants were determined and their variation with the solvent was compared with the prediction of the current electron transfer theories. It was found that for aprotic solvents the trend may be explained by the semiclassical theory for non-adiabatic electron transfer if a dielectric continuum model is used for the solvent. In hydroxylic solvents the rate constants do not fall on the same correlation, probably due to specific effects not taken into account by the model. (C) 1997 Elsevier Science S.A.