In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance: A Computational Study
In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance: A Computational Study
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DOI：
10.1021/jp409767r
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发表时间：
2014-03-20
影响因子：
3.7
通讯作者：
Ottosson, Henrik
中科院分区：
文献类型：
--
作者：
Emanuelsson, Rikard;Lofas, Henrik;Ottosson, Henrik
通过量子化学计算研究了通过E-E单键（E = C、Si、Ge或Sn）连接的1，4-二硅杂/锗杂/锡杂环己-2，5-二烯以及全碳1，4-环己二烯的低聚物，以努力鉴定作为分子“电线”的构象柔性分子线，其悬挂与共形无关的共轭和导电性质。我们的低聚物显示中性超共轭相互作用（σ/π共轭）之间相邻的σ（E-E）和π（C=C）键轨道，这些相互作用不随构象变化。甲基-，甲硅烷基-，和三甲基甲硅烷基（TMS）取代的1，4-二硅杂环己-2，5-二烯二聚体的最高占据分子轨道的能量和空间分布，以及稳定的构象的三聚体和四聚体，保持相当恒定的Si-Si键旋转。然而，在一些低聚物类型中，空间拥挤可能是一个问题。含硅四聚体的计算电导是类似的σ共轭线性所有反低聚硅烷（十六硅烷）在共轭路径中具有同样多的键。此外，Me取代的1，4-二硅杂环己二烯四聚体具有适度的电导波动与Si-Si键旋转时，电极-电极距离被锁定（变化的因子类似于30），而类似的TMS取代的四聚体在类似的条件下的波动更大。当电极-电极距离改变时，几种低聚物在某些距离间隔内显示出小的电导变化，例如，TMS取代的1，4-二硅杂环己-2，5-二烯四聚体的平均电导在9埃的电极-电极距离上几乎不变。
Oligomers of 1,4-disila/germa/stannacyclohexa-2,5-dienes as well as all-carbon 1,4-cyclohexadienes connected via E-E single bonds (E = C, Si, Ge, or Sn) were studied through quantum chemical calculations in an effort to identify conformationally flexible molecular wires that act as molecular "electrical cords" hang conformer-independent conjugative and conductive properties. Our oligomers display neutral hyperconjugative interactions (sigma/pi-conjugation) between adjacent sigma(E-E) and pi(C=C) bond orbitals, and these interactions do not change with conformation. The energies and spatial distributions of the highest occupied molecular orbitals of methyl-, silyl-, and trimethylsilyl (TMS)-substituted 1,4-disilacyclohexa-2,5-diene dimers, and stable conformers of trimers and tetramers, remain rather constant upon Si-Si bond rotation. Yet, steric congestion may be a concern in some of the oligomer types. The calculated conductances for the Si-containing tetramers are similar to that of a sigma-conjugated linear all-anti oligosilane (a hexadecasilane) with equally many bonds in the conjugated paths. Moreover, the Me-substituted 1,4-disilacyclohexadiene tetramer has modest conductance fluctuations with Si-Si bond rotations when the electrode-electrode distance is locked (variation by factor similar to 30), while the fluctuations under similar conditions are larger for the analogous TMS-substituted tetramer. When the electrode-electrode distance is changed several oligomers display small conductance variations within certain distance intervals, e.g., the mean conductance of TMS-substituted 1,4-disilacyclohexa-2,5-diene tetramer is almost unchanged over 9 A of electrode-electrode distances.