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Showing 1–7 of 7 results
Advanced filters: Author: Junpei Kuwabara Clear advanced filters
  • Supramolecular films consisting of guanosine derivatives modified with a tetrathiafulvalene moiety have been prepared. The hydrogen bonding network of the guanosine unit enables the formation of a robust and self-supporting cast film by a solution process. The self-supporting films were mechanically flexible. The physical properties of the films of the derivatives depended on both the length of the alkyl chains and the structure of their terminal group. The composite film of the derivatives with 7,7,8,8,-tetracyanoquinodimethane exhibited electrical conductivity.

    • Seong Jib Choi
    • Junpei Kuwabara
    • Takaki Kanbara
    Research
    Polymer Journal
    Volume: 44, P: 946-951
  • Direct arylation polycondensation has been investigated to develop efficient synthetic methods of conjugated polymers for use in optoelectronic applications. The optimization of reaction conditions achieved high molecular weights and minimal structural defects in the recurring structures. The optimized direct arylation method has several advantages over conventional methods, e.g., fewer synthetic steps, and high-molecular-weight and high-purity polymer. The high-quality polymeric materials exhibited superior performance to those obtained using a conventional method when used in organic photovoltaics and field-effect transistors.

    • Junpei Kuwabara
    Reviews
    Polymer Journal
    Volume: 50, P: 1099-1106
  • C–H/C–I direct arylation reactions for monomer synthesis and C–H/C–Br direct arylation polycondensation were investigated for the short-step synthesis of promising medium-bandgap polymers (PBDB-T) for OPV applications. Polycondensation and end-capping reactions using direct arylation have been established, enabling the synthesis of polymers without Br termini. The OPV performance of the synthesized polymer was lower than that of the benchmark polymer synthesized using the conventional method, despite having similar molecular weights. Possible factors for low OPV performance and future challenges include structural defects, impurities, and large molecular weight distribution.

    • Junpei Kuwabara
    • Kota Hiyaji
    • Takaki Kanbara
    Research
    Polymer Journal
    Volume: 55, P: 395-404
  • Direct arylation polycondensation using Pd(PCy3)2 as a precatalyst in N,N-diethylpropanamide as a reaction solvent afforded three types of the bithiazole-based conjugated polymers that have been difficult to synthesize under previously reported conditions using N,N-dimethylacetamide. The obtained polymers exhibited aggregation properties and high crystallinity. Control of aggregation was a key factor for increasing the power conversion efficiency of the organic photovoltaic devices fabricated from these polymers.

    • Junpei Kuwabara
    • Masahiro Kuramochi
    • Takaki Kanbara
    Research
    Polymer Journal
    Volume: 49, P: 123-131