Thermal with Electronic Excitation for the Unidirectional Rotation of a Molecule on Surface

TL;DR

This study investigates how thermal and electronic excitations influence the unidirectional rotation of a molecule on a surface, revealing conditions where heating enhances rotation and elucidating the role of electronic state mixing.

Contribution

It demonstrates the interplay between thermal and electron tunneling excitations in molecular rotation, highlighting how thermal energy contributes without violating microscopic reversibility.

Findings

Heating enhances rotational rate at moderate voltages and temperatures.

Inelastic tunneling dominates at higher voltages.

Thermal energy is transferred via electronic state mixing during tunneling.

Abstract

Exploring the limits of the microscopic reversibility principle, we investigated the interplay between thermal and electron tunneling excitations for the unidirectional rotation of a molecule-rotor on the Au(111) surface. We identified a range of moderate voltages and temperatures where heating the surface enhances the unidirectional rotational rate of a chemisorbed DMNI-P rotor. At higher voltage, inelastic tunneling effects dominate while at higher temperature the process becomes stochastic. At each electron transfer event during tunneling, the quantum mixing of ground and excited electronic states brings part of the surface thermal energy in the excited electronic states of the molecule-rotor. Thermal energy contributes therefore to the semi-classical unidirectional rotation without contradicting the microscopic reversibility principle.