Persistent C60 anion-radical formation via photoinduced electron transfer from tetraphenylborate and triphenylbutylborate

Photochemical reactions between photo-excited C-60 and borates (-BPh4 and -BPh3Bu) have been investigated by steady-state photolysis and laser flash photolysis. On steady-state photolysis of C-60 in the presence of the borates in polar solvents, the absorption of C-60(-.) increases with irradiation time, suggesting that irreversible photoinduced electron-transfer occurs. By the measurements of the transient absorption spectra, it is' indicated that electron transfer takes place from the borate anions to C-3(60)*, yielding C-60(-.) and (BPh3R)-B-. (R = Ph or Bu), in which the latter dissociates into Ph3B and R-., yielding biphenyl (or octane). Electron-donor ability of -BPh3 Bu is higher than that of -BPh4, while the steady-state photolysis to a C-60/borate system shows an opposite tendency. The addition reaction of C-60(-.) with Bu-. yielding BuC60- is more efficient than that with Ph-. producing PhC60-. The rate constant of electron-transfer via the triplet state of C-60 increases with solvent polarity.