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 3 C 60 by chloranil (CA) in CH 2 Cl 2 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 (ε = 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 arene +• cation radicals using visible light.