Orbital-selective single molecule excitation and spectroscopy based on plasmon-exciton coupling

TL;DR

This paper demonstrates a novel method for single-molecule excitation and spectroscopy using plasmon-exciton coupling via a scanning tunnelling microscope, enabling sub-molecular resolution and selective excitation.

Contribution

It introduces a new STM-based technique for localized single-molecule excitation and spectroscopy through plasmon-exciton interactions, with theoretical and experimental validation.

Findings

Coherent energy transfer between plasmon and molecular excitons was observed.

Polarized plasmonic fields enable selective excitation of molecular orbitals.

The method provides a platform for real-space investigation of excited states.

Abstract

The electronic excitation of molecules triggers diverse phenomena such as luminescence and photovoltaic effects, which are the bases of various energy-converting devices. Understanding and control of the excitations at the single-molecule level are long standing targets, however, they have been hampered by the limited spatial resolution in optical probing techniques. Here we investigate the electronic excitation of a single molecule with sub-molecular precision using a localised plasmon at the tip apex of a scanning tunnelling microscope (STM) as an excitation probe. Coherent energy transfer between the plasmon and molecular excitons is discovered when the plasmon is located in the proximity of isolated molecules, which is corroborated by a theoretical analysis. The polarised plasmonic field enables selective excitation of an electronic transition between anisotropic frontier molecular orbitals. Our findings have established the foundation of a novel single-molecule spectroscopy with STM, providing an integrated platform for real-space investigation of localised excited states.