Single-photon oxidation of C 60 by self-sensitized singlet oxygen.

C 60 is regarded as the most efficient singlet oxygen ( 1 O 2 ) photosensitizer. Yet, its oxidation by self-sensitized 1 O 2 remains unclear. The literature hints both oxygen and C 60 must be at excited states to react, implying a two-photon process: first, oxygen is photosensitized ( 1 C 60 • 1 O 2 ); second, C 60 is photoexcited ( 1 [Formula: see text]• 1 O 2 ). However, this scheme is not plausible in a solvent, which would quench 1 O 2 rapidly before the second photon is absorbed. Here, we uncover a single-photon oxidation mechanism via self-sensitized 1 O 2 in solvents above an excitation energy of 3.7 eV. Using excitation spectroscopies and kinetics analysis, we deduce photoexcitation of a higher energy transient, 3 [Formula: see text]• 3 O 2 , converting to 1 [Formula: see text]• 1 O 2 . Such triplet-triplet annihilation, yielding two simultaneously-excited singlets, is unique. Additionally, rate constants derived from this study allow us to predict a C 60 half-life of about a minute in the atmosphere, possibly explaining the scarceness of C 60 in the environment.