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

Photochemical reactions between photo-excited C₆₀ and borates (^-BPh₄ and ^-BPh₃Bu) have been investigated by steady-state photolysis and laser flash photolysis. On steady-state photolysis of C₆₀ in the presence of the borates in polar solvents, the absorption OfC₆₀^-• 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 ³C₆₀*, yielding C₆₀^-• and ^•BPh₃R (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 C₆₀/borate system shows an opposite tendency. The addition reaction of C₆₀^-• with Bu^• yielding BuC₆₀^- is more efficient than that with Ph^• producing PhC₆₀^-. The rate constant of electron-transfer via the triplet state of C₆₀ increases with solvent polarity.