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

Abstract

Photoinduced electron transfer between C 60 and tetrathiafulvalence (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 ( TC 60 ∗) observed in polar solvents decay on addition of 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 × 10 −3M. In benzene, the quenching of TC 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 TC 60 ∗, which were evaluated from the initial [ TC 60 ∗] and maximal [C 60 −] values, vary with the donor ability and solvent polarity. The forward electron transfer rate constant were evaluated from the decay rates of TC 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.