Oxidation of triplet C60 by hydrogen-bonded chloranil:: Efficient formation, spectrum and charge-shift reactions of C60+• cation radical

The rate of oxidative quenching of C-3(60) by chloranil (CA) in CH2Cl2 is much enhanced by added trifluoroacetic acid (TFA) or hexafluoro-2-propanol (HFIPA). These additives have similar hydrogen-bonding powers but differ widely in their proton acidities. In both cases, quenching rate constants calculated for H-bonded CA increase sharply with additive concentration. H-bonded clusters around the quinone are postulated in which electron transfer is coupled to fast protonation of CA(-.) by TFA, and strong H-bonding or solvation of charged radicals by HFIPA. This is consistent with observed neutral semiquinone formation, higher radical yields, and much slower back reactions for TFA. The C-60(+.) spectrum (epsilon = 25 000 +/- 2000 M-1 s(-1) at 980 nm) shows low absorption throughout the visible region. Charge-shift reactions Of C-60(+.) and arenes follow Rehm-Weller-Marcus kinetics and afford efficient preparation of arenel(+.) cation radicals using visible light.