Hideyuki Hosono

Photoinduced electron transfer in viologen-linked porphyrins (p-PCnV)

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.

Effect of configuration of viologen-linked porphyrin on photocurrent generation and on photoinduced hydrogen evolution

Two types of viologen-linked porphyrin with different configuration between the porphyrin and the bonded viologen have been synthesized and Langmuir–Blodgett (LB) films prepared. The effects of the different configurations on the photoelectric conversion by indium tin oxide (ITO) electrodes modified with the LB films and on photoinduced hydrogen evolution, using the LB films and H 2 PtCl 6 as a catalyst in the presence of ethylenediaminetetraacetic acid (EDTA) as a sacrificial electron donor, have been investigated. No effect was detected for the photocurrent generation but photoinduced hydrogen evolution was dependent upon the configuration. These results show that the rate of diffusion of small electrolyte ions is the same in both LB films but diffusion of large EDTA molecules is affected by the configuration. Hence, the molecular structure of viologen-linked porphyrin must be taken into account in order to make diffusion of reactant in the LB film easy and thus to increase the reaction yield.

Photoinduced electron transfer in viologen-linked porphyrins (m-PCnV)

Abstract Compounds containing a viologen linked to a porphyrin via a number (n = 3 – 6) of methylene groups were synthesized. Photoinduced long-range electron transfer between the porphyrin and the viologen is observed. The photoexcited singlet state of the porphyrin is quenched by the viologen in the viologen-linked porphyrins. The fluorescence decay profiles of the viologen-linked porphyrins consist of the sum of two first-order decays with short and long lifetimes. The short 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 viologen becomes less effective with increasing methylene chain length.