Controlling the entropy of a single-molecule junction

TL;DR

This paper demonstrates how thermocurrent spectroscopy can directly measure the entropy of a single-molecule junction, revealing microscopic electron transfer dynamics and a singlet-triplet transition undetectable by traditional methods.

Contribution

It introduces a novel thermoelectric measurement approach to determine entropy differences in single-molecule systems without prior structural assumptions.

Findings

Detected a singlet to triplet transition in a redox state

Uncovered microscopic electron transfer dynamics

Validated thermoelectric measurements as a tool for nanoscale entropy analysis

Abstract

Single molecules are nanoscale thermodynamic systems with few degrees of freedom. Thus, the knowledge of their entropy can reveal the presence of microscopic electron transfer dynamics, that are difficult to observe otherwise. Here, we apply thermocurrent spectroscopy to directly measure the entropy of a single free radical molecule in a magnetic field. Our results allow us to uncover the presence of a singlet to triplet transition in one of the redox states of the molecule, not detected by conventional charge transport measurements. This highlights the power of thermoelectric measurements which can be used to determine the difference in configurational entropy between the redox states of a nanoscale system involved in conductance without any prior assumptions about its structure or microscopic dynamics.