Design and Photo-functions of Self-assembled Nanolaminate Films

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In the present project a stacking hybrid film of mesoporous silica (MPS) and titania nanosheets (TNS) has been investigated, each of which include separately porphyrin dye (TMPyP) and methyl viologen (MV^<2+>), respectively. Under UV light irradiation, thus obtained hybrid film exhibits one electron oxidation of TMPyP accompanied by the simultaneous generation of one electron reduced MV^<2+>. That is, the result suggests an electron transfer through the interface of these inorganic thin films. In this year, the MPS/TNS hybrid film deposited on a FTO electrode was studied from the point of the generation of electric current through the inorganic interface.(MPS-TMPyP)/(TNS-MV^<2+>) hybrid film on the FTO electrode was immersed in CH_3CN together with Pt working and Ag/AgCl reference electrodes, and analyzed by measuring the photocurrent under UV light. On applying a negative vias voltage, -0.4V, a cathodic current, though weak, has been observed from the FTO electrode to MPS-TMPyP throug … More h TNS conduction band. For the observation of definite electric currents, an inversely stacked (TNS)/(MPS-TMPyP) hybrid film was attempted, where an electron acceptor, MV^<2+>, was removed from TNS interlayers by applying a positive vies voltage. By irradiation of the inversely stacked film by UV light, a strong anodic photocurrent flows through the inorganic interface into the FTO electrode. On the basis of spectroscopic observation, ca. 60% of the photocurrents induced the one-electron oxidation of TMPyP into the corresponding one-electron oxidized species.The resulting charge separation has been found to be quite stable and survived for a long period in this system. For instance, the formed one-electron oxidized TMPyP and the one-electron reduced MV^<2+> remain for several hours under the aerated conditions and ambient temperature. Especially under deaerated conditions the charge separation has a period of half decay of>several days. Now the present system is under the study for extending to a visible light sensitized charge-separation by visible light excitation of an appropriate organic dye with exothermic electron transfer to the conduction band of TNS semiconductor. Less