Solvent effects in the electron transfer quenching of the triplet state ofanthracene by p-benzoquinones

Here we present an investigation of the quenching of anthracene triplet by several p-benzoquinones, in two solvents of nearly equal macroscopic dielec tric properties, methanol and acetonitrile. Bimolecular quenching rate cons tants were measured by laser flash photolysis. Quantum efficiencies of char ge separation were also determined in the protic solvent. Quenching rate co nstants in acetonitrile follow a typical Rehm-Weller correlation for an ele ctron transfer process. Although free radical ions are observed in methanol , the rate constants are nearly independent on the driving force, at varian ce of the expected behavior. In this solvent, the charge separation quantum yield decreases when the energy of the ion-pair decreases, in agreement wi th the energy gap law.