ELECTRON TRANSFER FROM PHOTOEXCITED SINGLET AND TRIPLET BACTERIOPHEOPHYTIN

Abstract— Nanosecond and picosecond. kinetic techniques have been used to study electron transfer from the first excited singlet state (Bph*) and the first excited triplet state (Bph^T) of bacteriopheophytin to p‐benzoquinone. Quenching of the first excited singlet state by 40 mMp‐benzoquinone results in a decrease in the lifetime of Bph* but does not lead directly to the formation of the π‐cation radical (Bph†). In the presence of 8 M methyl iodide and 40 mMp‐benzoquinone together, the singlet lifetime is reduced further; however, the quantum yield of Bph^T is enhanced due to the increased rate of intersystem crossing between Bph* and Bph^T. Electron transfer from Bph^T to p‐benzoquinone leads to the formation and detection of Bph†. The results are discussed in terms of the spin‐selectivity of the reverse electron transfer process within the intermediate charge transfer complexes.