Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012, Bern, Switzerland.
J Am Chem Soc. 2013 Aug 21;135(33):12228-40. doi: 10.1021/ja4015293. Epub 2013 Aug 8.
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 βH range between 1.7 nm(-1) (CN) and 3.2 nm(-1) (SH) and show the following trend: βH(CN) < βH(NH2) < βH(BT) < βH(PY) ≈ βH(SH). DFT-based calculations yield lower values, which range between 0.4 nm(-1) (CN) and 2.2 nm(-1) (PY).
我们报告了一系列带有金触点的单分子结中寡炔分子线的电导率的长度依赖性和锚定基团依赖性的实验和理论研究。在实验中，我们专注于具有 n = 1、2 和 4 个三键的二芳基寡炔和锚定二氢苯并[b]噻吩（BT）的合成和性质。为了进行比较，我们还研究了亲金锚定基团氰基（CN）、氨基（NH2）、巯基（SH）和 4-吡啶基（PY）。扫描隧道显微镜断裂结（STM-BJ）和机械可控断裂结（MCBJ）技术用于研究单分子电导特性。与迄今为止研究过的传统锚定基团相比，BT 部分更具优势。BT 端基的寡炔具有 100%的结形成概率，并且具有研究的寡炔中最高的电导值，而且高于具有相似长度的其他共轭分子线。报告了具有 n = 1-4 个三键的寡炔的基于密度泛函理论（DFT）的计算。计算了每个分子家族的完整电导迹线和电导分布。锚定基团的滑动导致所研究的分子线的电导率和结合能都发生了振荡。与实验结果一致，BT 端基的寡炔被预测具有高电导率。实验衰减常数βH 在 1.7nm-1（CN）和 3.2nm-1（SH）之间变化，并表现出以下趋势：βH（CN）<βH（NH2）<βH（BT）<βH（PY）≈βH（SH）。基于 DFT 的计算得出的较低值在 0.4nm-1（CN）和 2.2nm-1（PY）之间变化。
