Design and Synthesis of Molecules which act as a catalyst for the Conversion of Solar Energy

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Photosynthesis, in which Nature converts the solar energy into useful energy, has been an ultimate goal for organic chemists. The critical event in the early stage of photosynthesis is the stable charge separation which is achieved by the several kinds of chromophores embedded in the protein matrix. The efficient forward- and inefficient back-electron transfers, responsible for the stable charge separation, are highly dependent upon the structural factors of the chromophores. One of the best strategy to understand these factors and to get information for the construction of artificial photosynthetic catalysts is to synthesize suitable model compounds. We have carried out our study along this line and got the following results. 1. We fixed our model compound with multistep electron transfer process into lipid bilayer and observed the photocurrent across the layer during irradiation. This indicates that the molecule really act as a catalyst for solar energy conversion. 2. We have prepared a (porphyrin)-(CH_2)_3-(quinone) compound with a long alkyl chain and fixed it into bovine serum alubumin. Unfortunately, we could not determine the effect of protein upon electron transfer since the porphyrin chromophore in protein did not show fluorescence. 3. We have synthesized model compounds, in which only the orientation of a porphyrin and a quinone is different and concluded that photoinduced electron transfer is fairly dependent upon the orientation of chromophores.