Photoinduced electron transfer (PET) within D4–A and D–A photosynthetic systems: Enhanced intramolecular PET achieved by increasing the number of donors

Photoinduced electron transfer (PET) occurring within D4–A was compared to that within D–A, in which A (electron acceptor) was a single zinc phthalocyanine moiety and D (electron donor) a phenothiazine unit, using UV–vis absorption, fluorescence emission and laser flash photolysis. D and A in both models were directly linked by covalent C–N bonds. The symmetrical D4–A system, for which both the synthesis and purification were more straigthforward than for D–A, displayed a much faster PET rate constant; although the D–A system was more difficult to prepare, it exhibited less efficient PET. The charge separation state formed through PET showed long lifetimes on the μs scale in the cases of both the D4–A and D–A molecules.