Electron transfer and energy transfer of photoexcited C₆₀ in the presence of retinols

Electron transfer and energy transfer between the photo-excited triplet state of C₆₀ (³C₆₀/*) and retinols, retinal and retinoic acid have been investigated by laser flash photolysis. In polar solvent, with the decay of the transient absorption band of ³C₆₀/* at 740 nm, the rise of the anion radical of C₆₀ (C₆₀ ^-*) at 1070 nm and cation radicals of retinols ['(retinols)⁺*] at 600 and 940 nm were observed in addition to the triplet state of retinols [³(retinols)*] at 400 nm. For retinal and retinoic acid, energy transfer occurs predominantly even in polar solvent, nevertheless the electron donor abilities of retinal and retinoic acid evaluated from the oxidation potentials are similar to those of retinols. The quantum yield and rate constant of electron transfer for trans-retinol are slightly faster than that for cis-retinol. After electron transfer, the cation radicals of retinols disappeared mainly by back electron transfer; however, some reactions of (retinols) ⁺* such as intra- and inter-molecular ring closing reactions also occur, yielding persistent C₆₀^-*.