Photoinduced electron transfer in viologen-linked porphyrins (p-PC n V)

Compounds containing a viologen linked to a porphyrin via a number (n= 4–7) of methylene groups have been synthesized and photoinduced long-range electron transfer between porphyrin and viologen was observed. The photoexcited singlet state of the porphyrin was quenched by the bonded viologen in viologen-linked porphyrins. The fluorescence decay profiles of the viologen-linked porphyrins consist of a sum of two first-order decays with shorter and longer lifetimes. The shorter lifetime arises from the direct quenching of the photoexcited singlet state of the porphyrin by the linked viologen. The intramolecular electron transfer process from the porphyrin to the bonded viologen becomes less effective when the methylene chain length becomes longer.