Dihydroazulene Photoswitch Operating in Sequential Tunneling Regime: Synthesis and Single-Molecule Junction Studies

Authors

  • Søren Lindbæk Broman,

    1. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
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  • Samuel Lara-Avila,

    1. Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivägen 9, S-41296 Göteborg, Sweden
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  • Christine Lindbjerg Thisted,

    1. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
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  • Andrew D. Bond,

    1. Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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  • Sergey Kubatkin,

    1. Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivägen 9, S-41296 Göteborg, Sweden
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  • Andrey Danilov,

    Corresponding author
    1. Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivägen 9, S-41296 Göteborg, Sweden
    • Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivägen 9, S-41296 Göteborg, Sweden.
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  • Mogens Brøndsted Nielsen

    Corresponding author
    1. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
    • Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
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Abstract

Molecular switches play a central role for the development of molecular electronics. In this work it is demonstrated that the reproducibility and robustness of a single-molecule dihydroazulene (DHA)/vinylheptafulvene (VHF) switch can be remarkably enhanced if the switching kernel is weakly coupled to electrodes so that the electron transport goes by sequential tunneling. To assure weak coupling, the DHA switching kernel is modified by incorporating p-MeSC6H4 end-groups. Molecules are prepared by Suzuki cross-couplings on suitable halogenated derivatives of DHA. The synthesis presents an expansion of our previously reported bromination–elimination–cross-coupling protocol for functionalization of the DHA core. For all new derivatives the kinetics of DHA/VHF transition has been thoroughly studied in solution. The kinetics reveals the effect of sulfur end-groups on the thermal ring-closure of VHF. One derivative, incorporating a p-MeSC6H4 anchoring group in one end, has been placed in a silver nanogap. Conductance measurements justify that transport through both DHA (high resistivity) and VHF (low resistivity) forms goes by sequential tunneling. The switching is fairly reversible and reenterable; after more than 20 “ON-OFF” switchings, both DHA and VHF forms are still recognizable, albeit noticeably different from the original states.

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