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 C60 and chloranil (CA) have been studied by complementary techniques of nanosecond laser photolysis and Fourier transform EPR. Direct oxidation of 3C60 by CA is slow (k = (2.0 ± 0.3) × 107 M-1 s-1), consistent with the high oxidation potential of 3C60. However, the formation rate and yield of CA- are much increased by addition of perylene (Pe) or tritolylamine (TTA) via the fast reactions 3C60 + Pe → C60 + 3Pe, followed by 3Pe + CA → Pe+ + CA-, or 3C60 + TTA → C60- + TTA+, followed by C60- + CA → C60 + CA-. These reactions utilize the broad absorption and initial high triplet yield of C60, as well as the low oxidation potential of 3Pe or high reduction potential of 3C60, to catalyze efficient formation of CA- and enhance separation of radicals. Triplet C60 also reacts with Pe by electron transfer, forming Pe+ and C60- 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 3Pe pathway. The extinction coefficient of C60- at 1080 nm is measured (ε = 18 300 ± 1100 M-1 cm-1) using the TTA reaction.