Direct Evidence of Interfacial Hydrogen Bonding in Proton-Electron Concerted 2D Organic Bilayer on Au Substrate

DOI Web Site 3 Citations 21 References
  • Yamamoto Susumu
    The Institute for Solid State Physics, The University of Tokyo
  • Kato Hiroyuki S.
    Department of Chemistry, Graduate School of Science, Osaka University
  • Ueda Akira
    The Institute for Solid State Physics, The University of Tokyo
  • Yoshimoto Shinya
    The Institute for Solid State Physics, The University of Tokyo
  • Hirata Yasuyuki
    The Institute for Solid State Physics, The University of Tokyo
  • Miyawaki Jun
    The Institute for Solid State Physics, The University of Tokyo
  • Yamamoto Kohei
    The Institute for Solid State Physics, The University of Tokyo
  • Harada Yoshihisa
    The Institute for Solid State Physics, The University of Tokyo
  • Wadati Hiroki
    The Institute for Solid State Physics, The University of Tokyo
  • Mori Hatsumi
    The Institute for Solid State Physics, The University of Tokyo
  • Yoshinobu Jun
    The Institute for Solid State Physics, The University of Tokyo
  • Matsuda Iwao
    The Institute for Solid State Physics, The University of Tokyo

Abstract

<p>Recent advances in the molecular design of organic materials have uncovered various novel functional properties. One of them is the coupling of proton dynamics and electrical conductivity, which can only be achieved in 3D organic crystals. However, reduction of dimensionality to two dimensions is essential in organic electronics application. In this study, we prepared and characterized a 2D organic bilayer with “proton-electron” concerted functionality on a solid surface. It consisted of catechol-fused bis(methylthio)tetrathiafulvalene (H2Cat-BMT-TTF) deposited onto an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on a Au surface. Direct evidence of interfacial hydrogen bonding (H-bonding) was obtained by scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM images showed the deposited H2Cat-BMT-TTF molecules as grains with the thickness of a single molecular layer. The OH stretching vibrational modes of H2Cat-BMT-TTF in the IRAS spectra showed a large red shift and substantial broadening upon adsorption on Im-SAM, indicating that the OH groups of H2Cat-BMT-TTF act as the H+ donor sites. The counterpart H+ acceptor sites were pinpointed by N K-edge NEXAFS. The π* peak of the imino N atoms of the imidazole rings in Im-SAM shifted to higher energy upon the adsorption of H2Cat-BMT-TTF. Therefore, H-bonds form between the imino N atoms (H+ acceptor sites) of Im-SAM and the OH groups (H+ donor sites) of H2Cat-BMT-TTF. The present work is a steady step toward the realization of 2D organic functional materials, and the experimental methods adopted herein will serve as powerful tools for the detection of their functions.</p>

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