Probing the Dynamics and Configurations of Single-Molecule Junctions via Seebeck Coefficient Spectroscopy

Single-molecule junctions exhibit dynamic structural configurations that strongly influence their electronic and thermoelectric properties. Here, we combine conductance (G) and Seebeck coefficient (S) measurements using the novel AC-based scanning tunneling microscope break-junction technique to probe the real-time evolution of oligo(phenylene ethynylene) molecular junctions. We show that most junctions undergo configuration changes that lead to notable changes in S, while G remains nearly constant. Density functional theory and quantum transport simulations link these observations to variations in contact geometry and charge transfer at the molecule-electrode interface. Our results demonstrate that simultaneous G and S measurements enable direct access to the dynamic reconfiguration of single-molecule junctions and offer design insights for thermoelectric molecular devices and new routes for increasing single-molecule junction stability.