Addressing the Dark State Problem in Strongly Coupled Organic Exciton-Polariton Systems

TL;DR

This paper demonstrates that by designing strongly coupled organic exciton-polariton systems with specific energy dispersions, it is possible to selectively excite polaritons and avoid the dark state reservoir, enabling better control of photochemical processes.

Contribution

The study introduces a method to selectively excite organic exciton-polaritons and overcome the dark state problem using momentum and spectral resolution in ultrafast measurements.

Findings

Selective excitation of polaritons achieved within 100 fs

Momentum scattering occurs on faster timescales than polariton decay

Dark state problem can be mitigated through system design

Abstract

The manipulation of molecular excited state processes through strong coupling has attracted significant interest for its potential to provide precise control of photochemical phenomena. However, the key limiting factor for achieving this control has been the dark state problem, in which photoexcitation populates long-lived reservoir states with similar energies and dynamics to bare excitons. Here, we use a sensitive ultrafast transient reflection method with momentum and spectral resolution to achieve the selective excitation of organic exciton-polaritons in open photonic cavities. We show that the energy dispersions of these systems allow us to avoid the parasitic effect of reservoir states. Under phase-matching conditions, we observe the direct population and decay of polaritons on time scales of less than 100 fs and find that momentum scattering processes occur on even faster timescales. We establish that it is possible to overcome the dark state problem through careful design of strongly coupled systems.