C60 as a Photocatalyst of Electron-Transfer Processes: Reactions of Triplet C60 with Chloranil, Perylene, and Tritolylamine Studied by Flash Photolysis and FT-EPR

Photoprocesses in benzonitrile solutions of C 60 and chloranil (CA) have been studied by complementary techniques of nanosecond laser photolysis and Fourier transform EPR. Direct oxidation of 3 C 60 by CA is slow ( k = (2.0 ± 0.3) × 10 7 M -1 s -1 ), consistent with the high oxidation potential of 3 C 60 . However, the formation rate and yield of CA - are much increased by addition of perylene (Pe) or tritolylamine (TTA) via the fast reactions 3 C 60 + Pe → C 60 + 3 Pe, followed by 3 Pe + CA → Pe + + CA -, or 3 C 60 + TTA → C 60 - + TTA +, followed by C 60 - + CA → C 60 + CA - . These reactions utilize the broad absorption and initial high triplet yield of C 60, as well as the low oxidation potential of 3 Pe or high reduction potential of 3 C 60, to catalyze efficient formation of CA - and enhance separation of radicals. Triplet C 60 also reacts with Pe by electron transfer, forming Pe + and C 60 - with rate one-third that of energy transfer. However, the CA - formed in the Pe-catalyzed reaction is strongly spin-polarized, indicating that it is formed primarily via the 3 Pe pathway. The extinction coefficient of C 60 - at 1080 nm is measured (ε = 18 300 ± 1100 M -1 cm -1 ) using the TTA reaction.