Enhanced π–π Stacking between Dipole-Bearing Single Molecules Revealed by Conductance Measurement,Journal of the American Chemical Society

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Enhanced π–π Stacking between Dipole-Bearing Single Molecules Revealed by Conductance Measurement
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-01-10 , DOI: 10.1021/jacs.2c09656
Chengyang Zhang ₁ , Jie Cheng ₂ , Qingqing Wu ₃ , Songjun Hou ₃ , Sai Feng ₁ , Bo Jiang ₄ , Colin J Lambert ₃ , Xike Gao ₂ , Yueqi Li ₁ , Jinghong Li _{1,

5}

Affiliation

Dipoles are widely involved in π–π interactions and are central to many chemical and biological functions, but their influence on the strength of π–π interactions remains unclear. Here, we report a study of π–π interaction between azulene-based, polar single molecules and between naphthalene-based, nonpolar single molecules. By performing scanning tunneling microscopy break junction measurements of single-molecule conductance, we show that the π-stacked dimers formed by the azulene-based, polar aromatic structures feature higher electrical conductivity and mechanical stability than those formed by the naphthalene-based, nonpolar molecules. Mechanical control of π–π interactions in both rotational and translational motion reveals a sensitive dependence of the stacking strength on relative alignment between the dipoles. The antiparallel alignment of the dipoles was found to be the optimal stacking configuration that underpins the observed enhancement of π–π stacking between azulene-based single molecules. Density functional theory calculations further explained the observed enhancement of stacking strength and the corresponding charge transport efficiency. Our experimental and theoretical results show that the antiparallel alignment of the dipole moments significantly enhances the electronic coupling and mechanical stability of π–π stacking. In addition, in the formation of single-molecule junctions, the azulene group was experimentally and theoretically proved to form a Au−π contact with electrodes with high charge transport efficiency. This paper provides evidence and interpretation of the role of dipoles in π–π interactions at the single-molecule level and offers new insights into potential applications in supramolecular devices.

中文翻译：

电导测量揭示偶极轴承单分子之间增强的 π-π 堆叠

偶极子广泛参与 π-π 相互作用，是许多化学和生物学功能的核心，但它们对 π-π 相互作用强度的影响仍不清楚。在这里，我们报告了基于甘菊环的极性单分子之间和基于萘的非极性单分子之间的 π-π 相互作用的研究。通过对单分子电导进行扫描隧道显微镜断裂结测量，我们表明，与基于萘的非极性分子形成的那些相比，由基于甘菊环的极性芳香结构形成的 π 堆叠二聚体具有更高的电导率和机械稳定性. 旋转和平移运动中 π-π 相互作用的机械控制揭示了堆叠强度对偶极子之间相对对准的敏感依赖性。偶极子的反平行排列被发现是最佳堆叠结构，它支持观察到的基于甘菊环的单分子之间 π-π 堆叠的增强。密度泛函理论计算进一步解释了观察到的堆积强度增强和相应的电荷传输效率。我们的实验和理论结果表明，偶极矩的反平行排列显着增强了 π-π 堆叠的电子耦合和机械稳定性。此外，在单分子结的形成中，实验和理论上证明了薁基团与电极形成 Au-π 接触，电荷传输效率高。

更新日期：2023-01-10

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