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Single-molecule conductance of functionalized oligoynes: length dependence and junction evolution

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  • Pavel Moreno-Garcia
  • Murat Gulcur
  • David Zsolt Manrique
  • Tom Pope
  • Wenjing Hong
  • Veerabhadrarao Kaliginedi
  • Cancan Huang
  • Andrei S. Batsanov
  • Martin R. Bryce
  • Colin Lambert
  • Thomas Wandlowski
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<mark>Journal publication date</mark>21/08/2013
<mark>Journal</mark>Journal of the American Chemical Society
Issue number33
Volume135
Number of pages13
Pages (from-to)12228-12240
Publication statusPublished
Original languageEnglish

Abstract

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with n = 1, 2, and 4 triple bonds and the anchor dihydrobenzo[b]thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH2), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with n = 1-4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants beta(H) range between 1.7 nm(-1) (CN) and 3.2 nm(-1) (SH) and show the following trend: beta(H)(CN) <beta(H)(NH2) <beta(H)(BT) <beta(H)(PY) approximate to beta(H)(SH). DFT-based calculations yield lower values, which range between 0.4 nm(-1) (CN) and 2.2 nm(-1) (PY).