Unraveling the dynamics of multiple excited states in a single-molecule transistor

Abstract

Characterizing charge transport through single molecules provides a fundamental route to explore correlated quantum states, forming the basis for nanodevices in which quantum effects govern operation. During the non-equilibrium electron transfer, a rich manifold of excited states emerges, whose dynamics encode many-body interactions at the single-molecule level. Disentangling these dynamics is crucial for understanding such interactions, however, it has remained elusive due to the experimental challenge of simultaneously achieving both high temporal and energy resolution. Here, we resolved the dynamics of multiple excited states during non-equilibrium charge transport through a single-molecule radical junction using nanosecond differential conductance spectroscopy. The participation of singlet and triplet states, mediated by doublet states, is revealed in both time and energy domains occurring within ~150 ns. In addition, the transient resonance positions evolve by up to ~440 meV over hundreds of nanoseconds, consistent with a dynamic realignment at the molecule–electrode interface during charge dissipation. We interpret this behavior as a signature of Coulomb-renormalized transport resonances rather than as direct evidence for isolated molecular eigenstates shifting in energy. These results provide insight into transient intermediates in single-molecule charge transport and suggest potential routes for controlling quantum states in molecular-scale devices.