Transition voltage spectroscopy reveals significant solvent effects on molecular transport and settles an important issue in bipyridine-based junctions
Transition voltage spectroscopy reveals significant solvent effects on molecular transport and settles an important issue in bipyridine-based junctions
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DOI：
10.1039/c3nr51290h
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发表时间：
2013-01-01
期刊：
影响因子：
6.7
通讯作者：
Baldea, Ioan
中科院分区：
文献类型：
--
作者：
Baldea, Ioan
一项开创性研究的结果（B。Xu和N. J. Tao，Science，2003，301，1221），基于置于溶剂中的联吡啶的单分子结最近受到了挑战（S. Y. Quek等人，Nat. Nano，2009，4，230），通过隐含地假设溶剂对分子传输的影响可忽略不计并且通过仅考虑低偏压电导数据。在本文中，我们证明了溶剂对分子输运的影响是重要的，为了证明这一点，我们将注意力集中在相对于电极费米能级的主导分子轨道（LUMO）的能量偏移量ε（0）上。为了从Xu和Tao提出的湿结的完整I-V曲线中估计能量偏移量ε（sol）（0），我们求助于最近提出的过渡电压谱（TVS）。TVS在本分析中起着关键作用，强调需要欧姆电导范围之外的数据来揭示溶剂的影响。我们表明，Δ S（sol）（0）与干结推导的能量偏移Δ S（0）（0）显著不同（J. R. Widawsky等人，Nano Lett.，2012，12，354）。目前的工作表明，溶剂对分子输运的影响是重要的，可以定量地理解。报道了有溶剂和无溶剂的从头计算结果，很好地解释了Δ ε（0）= ε（sol）（0）-ε（0）（0）的差异。Δ G（0）= Δ Δ G + Δ Phi + Δ W可以在具有明确物理内容的贡献中解开：溶剂化能（Δ Δ G），图像电荷（Δ Phi）和功函数（Δ W）。精确的分析公式为三角洲三角洲G和三角洲披报道，这提供了一个方便的框架来量化溶剂的影响，避免了苛刻的数值工作的实验。
Results of a seminal study (B. Xu and N. J. Tao, Science, 2003, 301, 1221) on the single-molecule junctions based on bipyridine placed in a solvent have been challenged recently (S. Y. Quek et al., Nat. Nano, 2009, 4, 230) by implicitly assuming a negligible solvent impact on the molecular transport and by merely considering low bias conductance data. In this paper we demonstrate that solvent effects on the molecular transport are important, and to show this we focus our attention on the energy offset epsilon(0) of the dominant molecular orbital (LUMO) relative to the electrode Fermi level. To estimate the energy offset epsilon(sol)(0) from the full I-V curves presented by Xu and Tao for wet junctions, we resort to the recently proposed transition voltage spectroscopy (TVS). TVS, which plays a key role in the present analysis, emphasizes that data beyond the ohmic conductance regime are needed to reveal the solvent impact. We show that epsilon(sol)(0) significantly differs from the energy offset epsilon(0)(0) deduced for dry junctions (J. R. Widawsky et al., Nano Lett., 2012, 12, 354). The present work demonstrates that solvent effects on molecular transport are important and can be understood quantitatively. Results of ab initio calculations with and without solvent are reported that excellently explain the difference delta epsilon(0) = epsilon(sol)(0) - epsilon(0)(0). delta epsilon(0) = Delta Delta G + delta Phi + delta W can be disentangled in contributions with a clear physical content: solvation energies (Delta Delta G), image charges (delta Phi), and work functions (delta W). Accurate analytical formulae for Delta Delta G and delta Phi are reported, which provide experimentalists with a convenient framework to quantify solvent effects obviating demanding numerical efforts.