Photoinduced single- and double-electron transfer in a photosynthetic model consisting of one-acceptor with four equally linked donors (D4–A)

Photoinduced electron transfer (PeT) process in a D4–A model, in which four p-amino-phenloxys (donor D) are covalently linked to a zinc phthalocyanine (acceptor A), was examined by laser flash photolysis and fluorescence technique. Not only does the usual intra-molecular photoinduced single-electron transfer occur from p-amino-phenloxy to the excited singlet state of A that forms the long-lived monoanion A− in the supermolecule with a fast rate of 25 ps, but also features different from PeT in the common D–A model were found. The free energy change, transient absorption spectra and associated decay kinetics strongly suggest that photoinduced intra-molecular double-electron transfer occurs concurrently from multidonors to the second lowest excited singlet state of A to form a double-charge separated state D2(D+)2–A2− because of the ability of zinc phthalocyanine to catch up to four electrons in the presence of four strong equal donors.