A molecular tetrad consisting of a free base porphyrin (P) linked to a triquinone moiety consisting of a naphthoquinone bearing two benzoquinones (NQ-BQ2) has been synthesized and its photochemistry has been investigated using time-resolved spectroscopic techniques. Excitation of the porphyrin chromophore of the P-NQ-BQ2 tetrad in benzonitrile solution is followed by photoinduced electron transfer with a rate constant of 8.3 × 1010 s-1 to produce an initial P.+-NQ.--BQ2 state with a quantum yield of unity. A charge shift reaction gives a final P.+-NQ-(BQ.-BQ) charge-separated state, which decays to the ground state with a rate constant of 1.9 × 1010 s-1. The tetrad features both sequential and parallel multistep electron-transfer pathways. No evidence was found for significant involvement of direct electron transfer from the porphyrin first excited singlet state to a benzoquinone.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry