Controlling the photon emission property of a single molecule is an important goal for nano-optics. We propose here a new mechanism for a single-molecule optical switch that utilizes the in situ electric field (EF) in biased metallic nanojunctions to control photon emission of molecules with through-space charge transfer (TSCT) excited states. The EF-induced Stark effect is capable of flipping the order of the bright noncharge transfer state and dark TSCT state, resulting in the anticipated switching behavior. The proposed mechanism was theoretically verified by scanning tunneling microscope-induced electroluminescence from a naphtalenediimide cyclophane molecule under experimentally accessible conditions. Simulations show that the proposed switching effect can be obtained by changing either bias polarity, which alters the polarization of the field, or tip-height, which affects the magnitude of the field. Our finding indicates that the in situ EF could play an important role in the design of optoelectronic molecular devices.

中文翻译：

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通过空间电荷转移状态的电场控制单分子光开关

控制单个分子的光子发射特性是纳米光学的一个重要目标。我们在这里提出了一种单分子光开关的新机制，它利用了原位偏置金属纳米结中的电场 (EF) 以控制具有通过空间电荷转移 (TSCT) 激发态的分子的光子发射。EF 诱导的斯塔克效应能够翻转亮非电荷转移状态和暗 TSCT 状态的顺序，从而产生预期的开关行为。通过在实验可接近的条件下，萘二亚胺环烷分子的扫描隧道显微镜诱导电致发光，从理论上验证了所提出的机制。模拟表明，可以通过改变偏置极性（改变场的极化）或尖端高度（影响场的大小）来获得所提出的开关效应。我们的发现表明原位 EF可以在光电分子器件的设计中发挥重要作用。