Synthesis of ViologenーLinked Porphyrins and Photoinduced Hydrogen Evolution with These Porphyrins

点击翻译按钮获取中文摘要

Porphyrins and viologens have been widely used as photosensitizers and electron carriers, respectively. In the viologen-linked porphyrin the photosensitizer and the electron carrying function are incorporated in the same molecule. In this study viologenーlinked porphyrins were synthesized and photoinduced electron transfer measured.The relative fluorescence intensities of the viologen-linked porphyrins were low compared with that of the porphyrin without viologen, indicating that the photoexcited singlet state was quenched by the viologen bonded to the porphyrin ring. In the case of viologenーlinked porphyrins, the fluorescence decay profiles can be described as a sum of two first order decays, one with a short lifetime (tau_S) and one with a long lifetimes (tau_L). The tau_L values of the viologenーlinked porphyrins are almost the same as that of the porphyrins without viologen. It is reasonable to assume that the fluorescence decay of the component with the longer lifetime is spontaneous and therefore independent of the type of viologens, bonded to the porpytrin ring and metnylene chain length. On the other hand, the shorter lifetime strongly depends on the methylene chain length and tau_S increases with increasing n except for n = 7. It may be concluded that the fluorescence decay of the component with shorter lifetime is due to the direct quenching of the photoexcited singlet state of the porphyrin by the linked viologen.