Atsushi Fujimoto

Kyoto University, Kioto, Kyōto, Japan

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Publications (4)

  • Hiroshi Imahori · Atsushi Fujimoto · Soonchul Kang · [...] · Seiji Isoda
    [Show abstract] [Hide abstract] ABSTRACT: Structure and photoelectrochemical properties of nanostructured SnO2 electrodes deposited electrophoretically with the composite clusters of porphyrin-modified gold nanoparticle with a long, flexible spacer and C60 molecules have been examined to obtain basic information on the development of organic solar cells with a high performance. The photoelectrochemical system with the long, flexible spacer between the porphyrin and the gold nanoparticle in the porphyrin-modified gold nanoparticle exhibited comparable external quantum yield in the UV–vis regions relative to porphyrin-modified gold nanoparticle with a relatively short spacer—C60 composite reference system. These results demonstrate that a suitable spacer to incorporate C60 molecules efficiently between the porphyrins in porphyrin-modified gold nanoparticles is a prerequisite for improving the performance of porphyrin and fullerene-based organic solar cells.
    Article · Feb 2006 · Tetrahedron
  • Hiroshi Imahori · Atsushi Fujimoto · Soonchul Kang · [...] · Helge Lemmetyinen
    [Show abstract] [Hide abstract] ABSTRACT: Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.
    Article · Dec 2005 · Chemistry
  • H Imahori · A Fujimoto · S Kang · [...] · S Isoda
    [Show abstract] [Hide abstract] ABSTRACT: A novel approach to constructing a light-energy conversion system using supramolecular incorporation of C60 molecules into tailored holes on porphyrin-modified gold nanoclusters in mixed solvent was reported. A porphyrin-alkanethiol mixed MPC (H2PC11(C15CO2H)MPC) was obtained by place-exchange reaction of the porphyrin MPC with 16-mercaptohexadecanoic acid in toluene for 12 h. Monochromatic light obtained by passing light from a 500 W xenon lamp through a monochromator was used for excitation. The design of such host structures on porphyrin MPCs provides a variety of ways for further development of more efficient light-energy conversion systems by modulating the surface structure.
    Article · Jul 2005 · Advanced Materials
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    [Show abstract] [Hide abstract] ABSTRACT: Novel organic solar cells have been prepared using quaternary self-organization of porphyrin (donor) and fullerene (acceptor) units by clusterization with gold nanoparticles on nanostructured SnO2 electrodes. First, porphyrin-alkanethiolate monolayer-protected gold nanoparticles (H2PCnMPC: n is the number of methylene groups in the spacer) are prepared (secondary organization) starting from the primary component (porphyrin-alkanethiol). These porphyrin-modified gold nanoparticles form complexes with fullerene molecules (tertiary organization), and they are clusterized in acetonitrile/toluene mixed solvent (quaternary organization). The highly colored composite clusters can then be assembled as three-dimensional arrays onto nanostructured SnO2 films to afford the OTE/SnO2/(H2PCnMPC+C60)m electrode using an electrophoretic deposition method. The film of the composite clusters with gold nanoparticle exhibits an incident photon-to-photocurrent efficiency (IPCE) as high as 54% and broad photocurrent action spectra (up to 1000 nm). The power conversion efficiency of the OTE/SnO2/(H2PC15MPC+C60)m composite electrode reaches as high as 1.5%, which is 45 times higher than that of the reference system consisting of the both single components of porphyrin and fullerene.
    Full-text available · Article · Mar 2005 · Journal of the American Chemical Society