Disentangling the components of a multiconfigurational excited state in isolated chromophore

TL;DR

This study combines light-STM experiments with theoretical modeling to visualize and disentangle the multiconfigurational excited states of a doublet in a PTCDA anion molecule, revealing their electronic structure and dynamics.

Contribution

It introduces a novel approach to directly visualize and manipulate multiconfigurational excited states at the single-molecule level using light-STM and theoretical analysis.

Findings

Bidirectional photocurrent varies with tip position.

Multiconfigurational state characterized as a superposition of two configurations.

Voltage control switches dominant electronic configurations.

Abstract

Studying the excited states of doublets is challenging for their typically multiconfigurational character. We employ light-scanning-tunneling microscopy (light-STM) to investigate photon-induced currents on a single open-shell PTCDA anion molecule placed into a plasmonic nanocavity between a tip and a substrate, irradiated by laser. Submolecular mapping reveals a zero-bias bidirectional photocurrent strongly varying with the lateral position of the tip apex above the molecule. We elucidate the mechanism in terms of a theoretical model in which a multiconfigurational doublet state is excited and decays back to the anion ground state through sequential electron transfers with the tip and the substrate. The correspondence of the experimental and theoretical contrast proves the correlated character of the excited state which can be described as a superposition of two dominating electronic configurations. By applying bipolar voltage on the junction with the molecule, we switch the dominant recombination pathway from one of the configurations to the other, effectively disentangling the multiconfigurational state individual components through visualization of their Dyson orbitals, as corroborated by theoretical modelling.