CHARGE-TRANSFER ACROSS OBLIQUE BISPORPHYRINS - 2-CENTER PHOTOACTIVE MOLECULES

A bisporphyrin, comprising gold(III) and zinc(II) porphyrins held in an oblique orientation via a 1,10-phenanthroline spacer, undergoes intramolecular electron transfer with almost unit quantum efficiency on excitation with visible light. The reaction pathway and kinetics vary according to which porphyrin absorbs the incident photon, but the net reaction involves intramolecular electron transfer from zinc porphyrin (ZnP) to gold porphyrin (AuP+). Thus, the ZnP excited singlet state transfers an electron to the appended AuP+. Excitation of the AuP+ generates the triplet excited state which abstracts an electron from the ZnP (77%) or transfers electronic energy to it ( 15%). The ZnP triplet state also transfers an electron to the appended AuP+. Similar processes are observed with the corresponding gold/free-base bisporphyrin.