Permethylation Introduces Destructive Quantum Interference in Saturated Silanes
Permethylation Introduces Destructive Quantum Interference in Saturated Silanes
复制标题
全甲基化在饱和硅烷中引入破坏性量子干扰
DOI：
10.1021/jacs.9b06965
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发表时间：
2019-10-02
影响因子：
15
通讯作者：
Solomon, Gemma C.
中科院分区：
文献类型：
--
作者：
Garner, Marc H.;Li, Haixing;Solomon, Gemma C.
由于顺式二面角沿着分子骨架的构象中的破坏性量子干涉，硅烷的单分子电导被抑制。然而，尽管结构上的相似性，σ干扰效应尚未观察到烷烃。在这里，我们报告说，硅烷中使用的甲基取代基是在这些系统中的σ干扰的先决条件。通过密度泛函理论计算，我们发现，在非甲基化硅烷的破坏性干涉是不明显的，以同样的程度。我们发现烷烃中也是如此，因为全甲基化环状和双环烷烃中的传输被显着抑制。使用扫描隧道显微镜断裂结方法，我们确定官能化环己烷和双环[2.2.2]辛烷的单分子电导被发现是高于等效的全甲基化硅烷。而不是在分子骨架中的碳和硅原子之间的差异，我们的计算表明，它主要是氢和甲基取代基之间的差异，导致在不同的电子传输性能的非甲基化烷烃和全甲基化硅烷。化学取代基在决定饱和分子的单分子电导方面起着重要的作用，在改进和扩展绝缘有机分子的化学设计时必须考虑这一点。
The single-molecule conductance of silanes is suppressed due to destructive quantum interference in conformations with cisoid dihedral angles along the molecular backbone. Yet, despite the structural similarity, sigma-interference effects have not been observed in alkanes. Here we report that the methyl substituents used in silanes are a prerequisite for sigma-interference in these systems. Through density functional theory calculations, we find that the destructive interference is not evident to the same extent in nonmethylated silanes. We find the same is true in alkanes as the transmission is significantly suppressed in permethylated cyclic and bicyclic alkanes. Using scanning tunneling microscope break-junction method we determine the single-molecule conductance of functionalized cyclohexane and bicyclo[2.2.2]octane that are found to be higher than that of equivalent permethylated silanes. Rather than the difference between carbon and silicon atoms in the molecular backbones, our calculations reveal that it is primarily the difference between hydrogen and methyl substituents that result in the different electron transport properties of nonmethylated alkanes and permethylated silanes. Chemical substituents play an important role in determining the single-molecule conductance of saturated molecules, and this must be considered when we improve and expand the chemical design of insulating organic molecules.