Efficient photoinduced electron transfer between C-60 and tetrathiafulvalenes studied by nanosecond laser photolysis

Photoinduced electron transfer between C-60 and tetrathiafulvalene (TTF) or bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF) in polar and non-polar solvents and their mixtures was investigated by nanosecond laser photolysis/transient absorption spectroscopy in the visible and near-IR regions. The transient absorption bands of the C-60 triplet (C-T(60)*) observed in polar solvents decay on addition TTF (or BEDT-TTF), accompanied by the appearance of the transient absorption bands of C-60(.-). The yields of C-60(.-) are decreased on addition of O-2, revealing that about 10% of C-60(.-) is produced via the singlet state at donor concentrations of less than 5 x 10(-3) M. In benzene, the quenching of C-T(60)* without the appearance of C-60(.-) within the nanosecond laser pulse is attributed to collisional quenching. The quantum efficiencies of C-60(.-) formation via C-T(60)*, which were evaluated from the initial [C-T(60)*] and maximal [C-60(.-)] values, vary with the donor ability and solvent polarity. The forward electron transfer rate constants were evaluated from the decay rates of C-T(60)* (or the rise rates of C-60(.-)) after multiplying by the quantum efficiencies. The back electron transfer rates are slowed down in polar solvents. (C) 1997 Elsevier Science S.A.