Photoinduced electron transfer from N,N-dimethylaniline to pyrrolidinofullerenes (C60(C3H6N)R):: Emphasized substituent effects with solvent polarity change

Photoinduced electron-transfer reactions of pyrrolidinofullerenes {C-60(C3H6N)R; R = H (1), C6H4NO2-p (2), C6H4CHO-p (3), C6H5 (4), C6H4OMe-p (5), and C6H4NMe2-p (6)} with N,N-dimethylaniline have been systematically studied by means of nanosecond laser photolysis. From the direct observation of the rises of the anion radicals accompanied by the decays of the triplet states of the fullerenes, the rate constants of electron-transfer reactions (k(ET)) via the triplet states were evaluated in polar solvents. Although the k(ET) values are considerably decreased by the substituents as compared with that of pristine C-60, the electron is accepted by the C-60 moiety. Among the derivatives, the k(ET) values of 2 and 3 with electron-withdrawing groups are larger than those of 4 and 1. In less polar solvent, such a substituent effect becomes prominent with decrease in the k(ET) values, which is in accord with the reactivity-selectivity principle. This behavior can be explained by the Rehm-Weller relation and/or Marcus equation in consideration of the solvent polarity change. Back-electron-transfer rate constants in less polar solvent are larger than those in polar solvent, which is related to the desolvation process and/or loose ion pair formation.