C-60 as a photocatalyst of electron-transfer processes: Reactions of triplet C-60 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 C-3(60) by CA is slow (k = (2.0 +/- 0.3) x 10(7) M(-1) s(-1)), consistent with the high oxidation potential of C-3(60). However, the formation rate and yield uf CA(-) are much increased by addition of perylene (Pe) or tritolylamine (TTA) via the fast reactions C-3(60) + Pe --> C-60 + (3)Pe, followed by (3)Pe + CA --> Pe(+) + CA(-), or C-3(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 C-3(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-calalyzed 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. (epsilon = 18 300 +/- 1100 M(-1) cm(-1)) using the TTA reaction.