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

Abstract

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 of C₆₀^–˙ 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.