单分子尺度的光量子态调控与单分子电致发光研究

Single-molecule electroluminescence and its relevant latest progress

分子尺度上的光电相互作用研究可以为发展未来信息和能源技术提供科学基础.扫描隧道显微镜不仅可以用来观察和操纵纳米世界中的原子和分子,而且其高度局域化的隧穿电流还可以被用来激发隧道结中的分子,使之发光,以研究局域场下的分子光电特性.本文综述了中国科学技术大学单分子光电研究组近期在锌酞菁分子电致发光方面取得的科学进展,包括:1)利用有效的电子脱耦合与纳腔等离激元调控技术,实现了隧穿电子激发下的单个锌酞菁分子的电致荧光,并通过发展相关的光子发射统计测量方法,表征了单个分子在隧穿电子激发下的电致荧光具有单光子发射特性; 2)发展了具有亚纳米空间分辨的荧光光谱成像技术,实现了对酞菁分子间相干偶极相互作用特征的实空间观察; 3)对分子与纳腔等离激元之间的相干耦合作用进行了亚纳米精度的操控,在单分子水平上观察到了法诺共振和兰姆位移效应.这些研究结果不仅为研发基于有机分子的电泵纳米光源与单光子光源等分子光电器件提供了新的思路,而且为在单分子尺度上研究分子光电特性、分子间能量转移以及场与物质之间的相互作用规律等提供了新的表征方法.

Research on the interaction and interconversion between electrons and photons on an individual molecular scale can provide scientific basis for the future developing of information and energy technology. Scanning tunneling microscope（STM） can offer abilities beyond atomic-resolution imaging and manipulation, and its highly localized tunneling electrons can also be used for exciting the molecules inside the tunnel junction, generating molecule-specific light emission, and thus enabling the investigation of molecular optoelectronic behavior in local nano-environment. In this paper,we present an overview of our recent research progress related to the single-molecule electroluminescence of zinc phthalocyanine（ZnPc） molecules. First, we demonstrate the realization of single-molecule electroluminescence from an isolated ZnPc by adopting a combined strategy of both efficient electronic decoupling and nanocavity plasmonic enhancement. By further combining the photon correlation measurements via the Hanbury-Brown-Twiss interferometry with STM induced luminescence technique, we demonstrate and confirm the single-photon emission nature of such an electrically driven single-molecule electroluminescence. Second, by developing the sub-nanometer resolved electroluminescence imaging technique, we demonstrate the real-space visualization of the coherent intermolecular dipole-dipole coupling of an artificially constructed non-bonded ZnPc dimer. By mapping the spatial distribution of the photon yield for the excitonic coupling in a well-defined molecular architecture, we can reveal the local optical response of the system and the dependence of the local optical response on the relative orientation and phase of the transition dipoles of the individual molecules in the dimer. Third, by using a single molecular emitter as a distinctive optical probe to coherently couple with the highly confined plasmonic nanocavity, we demonstrate the Fano resonance and photonic Lamb shift at a single-molecule level. The ability to spatially control the single-molecule Fano resonance with sub-nanometer precision can reveal the coherent and highly confined nature of the broadband nanocavity plasmon, as well as the coupling strength and the anisotropy of the field-matter interaction. These results not only shed light on the fabrication of electrically driven nano-emitters and single-photon sources, but also open up a new avenue to the study of intermolecular energy transfer, field-matter interaction, and molecular optoelectronics, all at the single-molecule level.