Photoinduced Electron Transfer in a Porphyrin Dyad

Article abstract of DOI:10.1021/j100132a021

A porphyrin dyad designed to facilitate vectorial interporphyrin electron transfer has been synthesized and studied using steady-state and time-resolved absorption and emission spectroscopies.The dyad features a zinc tetraarylporphyrin bearing electron-donating substituents linked by an amide bond to a free base porphyrin carrying electron-withdrawing groups.Excitation of the zinc porphyrin moiety in dichloromethane solution is followed by singlet energy transfer to the free base and concurrent electron transfer to the same moiety to yield a charge-separated state.The free base first excited singlet state decays by accepting an electron from the zinc porphyrin to form the same charge-separated state.Similar results are observed in butyronitrile.Transient absorption studies in butyronitrile verify the formation of a short-lived (8 ps) charge-separated state from the porphyrin first excited singlet states.The results support the suggestion that fluorescence quenching in related porphyrin dyads and carotenoid-diporphyrin triads is due to photoinduced electron transfer, rather than some other decay processes.