Persistent C_(60) anion-radical formation via photoinduced electron transfer from tetraphenylborate and triphenylbutylborate

摘要

Photochemical reactions between photo-excited C_(60) and borates (~-BPh_4 and ~-BPh_3Bu) 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)~(- centre dot) 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 ~3C_(60)~*, yielding C_(60)~(- centre dot) and ~(centre dot)BPh_3R (R = Ph or Bu), in which the latter dissociates into Ph_3B and R~(centre dot), yielding biphenyl (or octane). Electron-donor ability of ~-BPh_3 Bu is higher than that of ~-BPh_4, while the steady-state photolysis to a C_(60)/borate system shows an opposite tendency. The addition reaction of C_(60)~(- centre dot) with Bu~(centre dot) yielding BuC_(60)~- is more efficient than that with Ph~(centre dot) producing PhC_(60)~-. The rate constant of electron-transfer via the triplet state of C_(60) increases with solvent polarity.