| Research Abstract |
Self-Assembled electron donor-acceptor linked systems play a very important role in the artificial photosynthetic system because of the easy way to keep the short distance between the electron donor and acceptor. The various researches for the artificial photosynthesis with covalently linked donor-acceptor systems exist. In this work we established the self-assembled zinc porphyrin and fullerence[C60]system to build up the supramolecules containing them and to achieve the photoinduced electron transfer reactions with high efficiency and the long-lived charge separated state like a photosynthetic reaction center. In these supramolecular systems, efficient charge separation was confirmed by the time-resolved fluorescence measurements and by the fs-ps transient absorption methods. The lifetimes of charge-separated states were determined by the ns transient spectra in near IR region.
The pyridine and imodazole moieties were introduced on C_<60> to construct the supramolecular systems via coordination bonds between zinc porphyrin. In the case of imodazole, we obtained the higher equilibrium constant in the formation of the supramolecule and the high efficiency of the charge separation. The higher equilibrium constant for axial coordination was obtained at low temperature. This means that the more efficient charge separation occurred at the low temperature.
On the other hand, we found that the supramolecular systems in rotaxanes containing C_<60> and porphyrin. In these systems, C_<60> has a ring to catch the axel, which has porphyrin as a stopper. By the time-resolved fluorescence and transient absorption measurements, we found the efficient intra-rotaxane charge separation and long-lived charge separated state in these rotaxane. Interestingly, we found the size dependency of the charge separation type ; the change separation starts from the excited singlet state in the small rotaxane, however, it starts from the excited triplet state in the large one.
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