Observation of dielectric enrichment upon the formation of benzophenone radical anion in a binary solvent mixture

In this paper we present results about the non-linear solvatochromic shift of the benzophenone radical anion absorption maximum in dimethyl sulfoxide-1,2-dichloroethane mixtures as a function of solvent mole fraction. Because of the non-hydrogen bonding character of the solvents, the observed absorption shift is attributed to dielectric enrichment only. The mathematical model which was developed for neutral dipolar solutes is extended to ionic species of charge q and molecular radius r; the preferential solvation index is proportional to q(2)r(-4). In the present case its value is larger than those observed in most cases of dipolar solutes.