Single-photon oxidation of C₆₀ by self-sensitized singlet oxygen

C₆₀ is regarded as the most efficient singlet oxygen (¹O₂) photosensitizer. Yet, its oxidation by self-sensitized ¹O₂ remains unclear. The literature hints both oxygen and C₆₀ must be at excited states to react, implying a two-photon process: first, oxygen is photosensitized (¹C₆₀•¹O₂); second, C₆₀ is photoexcited (¹[Formula: see text]•¹O₂). However, this scheme is not plausible in a solvent, which would quench ¹O₂ rapidly before the second photon is absorbed. Here, we uncover a single-photon oxidation mechanism via self-sensitized ¹O₂ 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]•³O₂, converting to ¹[Formula: see text]•¹O₂. Such triplet-triplet annihilation, yielding two simultaneously-excited singlets, is unique. Additionally, rate constants derived from this study allow us to predict a C₆₀ half-life of about a minute in the atmosphere, possibly explaining the scarceness of C₆₀ in the environment.