Electrofluorochromism at the single molecule level

TL;DR

This study uses scanning tunneling microscopy to investigate and control the fluorescence of a single molecule at the atomic level, revealing how oxidation states influence optical properties and how emission can be manipulated.

Contribution

It demonstrates the ability to probe and control single-molecule fluorescence and charge states using STM, providing insights into fundamental mechanisms at the molecular scale.

Findings

Distinct fluorescence spectra for neutral and oxidized states.

Emission controlled by insulator thickness and tip plasmons.

Sub-nanometric tip variations reveal charging and electroluminescence mechanisms.

Abstract

The interplay between the oxidation state and the optical properties of molecules plays a key role for applications in displays, sensors or molecular-based memories. The fundamental mechanisms occurring at the level of a single-molecule have been difficult to probe. We used a scanning tunneling microscope (STM) to characterize and control the fluorescence of a single Zn-phthalocyanine radical cation adsorbed on a NaCl-covered Au(111) sample. The neutral and oxidized states of the molecule were identified on the basis of their fluorescence spectra that revealed very different emission energies and vibronic fingerprints. The emission of the charged molecule was controlled by tuning the thickness of the insulator and the plasmons localized at the apex of the STM tip. In addition, sub-nanometric variations of the tip position were used to investigate the charging and electroluminescence mechanisms.