Journal of the American Chemical Society, Vol.119, No.6, 1400-1405, 1997
Photoinduced Charge Separation and Charge Recombination to a Triplet-State in a Carotene-Porphyrin-Fullerene Triad
A molecular triad consisting of a diarylporphyrin (P) covalently linked to a carotenoid polyene (C) and a fullerene (C-60) has been prepared and studied using time-resolved spectroscopic methods. In 2-methyltetrahydrafuran solution, the triad undergoes photoinduced electron transfer to yield C-P-.+-C-60(.-), which evolves into C-.+-P-C-60(.-) With an overall quantum yield of 0.14. This state decays by charge recombination to yield the carotenoid triplet state with a time constant of 170 ns. Even in a glass at 77 K, C-.+-P-C-60(.-) is formed with a quantum yield of similar to 0.10 and again decays mainly by charge recombination to give C-3-P-C-60. The fullerene triplet, formed through normal intersystem crossing, is also observed at 77 K. The generation in the triad of a long-lived charge separated state by photoinduced electron transfer, the low-temperature electron transfer behavior, and the formation of a triplet state by charge recombination are phenomena previously observed mostly in photosynthetic reaction centers.
Keywords:INTRAMOLECULAR ELECTRON-TRANSFER;REACTION CENTERS;PHOTOPHYSICAL PROPERTIES;ENERGY-TRANSFER;C-60;PHOTOSYNTHESIS;BACTERIOCHLOROPHYLL;CAROTENOPORPHYRINS;PHOSPHORESCENCE;MIMICRY