通过等离激元皮米腔分子振动谱观测偶氮苯单分子化学过程

Picocavity Plasmon-Enhanced Vibrational Spectroscopy of Single-Molecule Chemical Processes of 4,4'-Dimercaptoazobenzene

基于等离激元增强机制的拉曼散射测量技术能够将分子的拉曼散射截面扩大几个数量级,在痕量物质鉴定和追踪领域中具有广阔的应用前景。当增强因子达到1010量级左右时,人们已经能够实现对单个分子的识别,而在单分子水平追踪物理和化学行为也将获得比基于大量分子统计学行为的系综测量技术更加丰富和精细的观测结果。通过采用径向偏振激光激发纵向等离激元天线中的皮米腔热点,实现了对化学反应过程基于单分子振动光谱的实时精细观测。观察到了4-硝基苯硫醇二聚化为偶氮苯,以及单个偶氮苯分子从反式(Trans)构象短暂切换到顺式(Cis)并与金原子脱吸附的过程。该研究展现了等离激元皮米腔分子振动谱技术在单分子化学动力学研究中的部分潜力。

Raman scattering measurement technology based on plasmon enhancement mechanism can improve the Raman scattering crosssections of molecules by several orders of magnitude.Accordingly,they have a wide range of application prospects for trace substance identification and tracking.Many previous studies have reported identification of singlemolecules when the enhancement factor reaches~1010.Measuring physical and chemical behaviors at the singlemolecule level is expected to provide richer and more accurate results compared to measuring the statistical behavior of an ensemble of many molecules.This study uses a radially polarized laser to excite a picocavity hotspot in a longitudinally polarized plasmonic antenna.We achieve an accurate observation of the chemical processes of individual molecules using their vibrational spectra.In particular,we observe that 4-nitrobenzenethiol dimerized into 4,4'-dimercaptoazobenzene and that a singlemolecule of the latter briefly switched from trans-to cisconformation;it then desorbs from the gold atom and reverts to transconformation.This study preliminarily shows the power of picocavity plasmonenhancedvibrational spectroscopy in investigating singlemoleculechemical kinetics.