Schosser Werner M, Hsu Chunwei, Zwick Patrick, Beltako Katawoura, Dulić Diana, Mayor Marcel, van der Zant Herre S J, Pauly Fabian
Institute of Physics, University of Augsburg, 86135 Augsburg, Germany.
Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, Delft 2628 CJ, The Netherlands.
Nanoscale. 2022 Jan 20;14(3):984-992. doi: 10.1039/d1nr06484c.
The possibility to study quantum interference phenomena at ambient conditions is an appealing feature of molecular electronics. By connecting two porphyrins in a cofacial cyclophane, we create an attractive platform for mechanically controlling electric transport through the intramolecular extent of π-orbital overlap of the porphyrins facing each other and through the angle of xanthene bridges with regard to the porphyrin planes. We analyze theoretically the evolution of molecular configurations in the pulling process and the corresponding changes in electric conduction by combining density functional theory (DFT) with Landauer scattering theory of phase-coherent elastic transport. Predicted conductances during the stretching process show order of magnitude variations caused by two robust destructive quantum interference features that span through the whole electronic gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Mechanically-controlled break junction (MCBJ) experiments at room temperature verify the mechanosensitive response of the molecular junctions. During the continuous stretching of the molecule, they show conductance variations of up to 1.5 orders of magnitude over single breaking events. Uncommon triple- and quadruple-frequency responses are observed in periodic electrode modulation experiments with amplitudes of up to 10 Å. This further confirms the theoretically predicted double transmission dips caused by the spatial and energetic rearrangement of molecular orbitals, with contributions from both through-space and through-bond transport.
在环境条件下研究量子干涉现象的可能性是分子电子学的一个吸引人的特点。通过在共面环番中连接两个卟啉，我们创建了一个有吸引力的平台，用于通过面对面的卟啉分子内π轨道重叠程度以及氧杂蒽桥相对于卟啉平面的角度来机械控制电输运。我们通过将密度泛函理论（DFT）与相位相干弹性输运的朗道尔散射理论相结合，从理论上分析了拉伸过程中分子构型的演变以及相应的电导变化。拉伸过程中预测的电导显示出由两个强大的破坏性量子干涉特征引起的数量级变化，这些特征贯穿最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）之间的整个电子能隙。室温下的机械控制断结（MCBJ）实验验证了分子结的机械敏感响应。在分子的连续拉伸过程中，它们在单个断裂事件中显示出高达1.5个数量级的电导变化。在振幅高达10 Å的周期性电极调制实验中观察到了不常见的三倍频和四倍频响应。这进一步证实了由分子轨道的空间和能量重排引起的理论预测的双传输下降，包括空间传输和键传输的贡献。
