Role of Delocalization to Polariton Chemistry

Wei Xiong University of California San Diego

Polaritons, quasiparticles resulting from the strong collective coupling of light and matter, have demonstrated remarkable capabilities to alter chemical reactions, energy, and charge transport processes. These features have the potential to revolutionize the control of molecular properties. A key characteristic of polaritons is their delocalized wavefunctions, a hallmark of their behavior. In many chemical systems, energy disorder is prevalent, and delocalization in polariton systems has been assumed to be robust against this disorder. In our investigation, we examined the criteria necessary to maintain delocalization in molecular polaritons. Contrary to previous assumptions, our study reveals that energy disorder disrupts delocalization in polaritons. To restore delocalization and mitigate the effects of disorder, the collective coupling strength must exceed three times the inhomogeneous linewidth. We further present experimental evidence to show the importance to reach delocalization in order to achieve polariton-enabled energy transfer and modification to reaction dynamics.

This finding suggests a more stringent criterion for preserving the unique characteristics of polaritons than the conventional standard, which considers collective coupling strengths larger than photonic and molecular spectral linewidths. Moreover, we present a simple linear spectroscopic method to quantify the relative levels of delocalization. This work provides insights into why the onset of modified dynamics exceeds the strong coupling criteria, offering an important measure of polariton delocalization for chemical and materials research under strong coupling.1

[1] Tianlin Liu, Guoxin Yin, Wei Xiong, Unlocking Delocalization: How Much Coupling Strength can Overcome Energy Disorder in Molecular Polaritons?, 10.26434/chemrxiv-2024-zfbs2