Locally-Induced Stark Shifts of Collective Excitonic Modes in Polyradical Aggregates

TL;DR

This experimental study demonstrates local electric field control over collective excitonic states in radical chromophore aggregates using tip-enhanced photoluminescence spectroscopy, revealing Stark shifts and spectral modifications.

Contribution

It introduces a method to actively manipulate dark and bright excitonic modes in molecular aggregates via local electric fields, advancing nanoscale optoelectronic control.

Findings

Proportional Stark shifts observed in excitonic spectra.

Dark states exhibit emission peak sharpening under electric fields.

Bright and dark states show divergent behaviors depending on measurement position.

Abstract

Active control of dark long-lived excitonic states in molecular aggregates using local electric fields is a pivotal challenge for advancing nanoscale optoelectronics and quantum device engineering. This experimental study investigates the collective excitonic states in aggregates composed of radical chromophores. With the strong optical enhancement provided by tip-enhanced photoluminescence (TEPL) spectroscopy, bright and dark excitonic modes are observed emerging due to interexciton coupling and induce changes in their spectra with the electric field locally applied within the nanocavity gap. Proportionally scaling Stark shifts are revealed as well as the emission peak sharpening of the dark states and a divergent behavior of the bright states in asymmetric measurement positions of the nanocavity above the aggregates. The observed complex behavior is discussed in terms of influence of the field, molecule arrangement, nanocavity coupling, dark mode lifetimes and electrostatic charge inhomogeneities in the clusters. This sensitivity to the external parameters demonstrates an effective means of control over radical excitonic aggregates.