Freezing molecules with light: How long can one maintain a non-equilibrium molecular geometry by strong light-matter coupling?

TL;DR

This paper explores how strong light-matter coupling in optical microcavities can extend the non-equilibrium molecular geometries' lifetime, potentially controlling chemical reactivity by 'freezing' molecules in excited states for tens to thousands of picoseconds.

Contribution

It provides a theoretical estimate of how non-equilibrium molecular configurations can be maintained longer using strong light-matter coupling, highlighting the role of polariton states.

Findings

Upper polaritons can lock molecules in their ground state geometries for tens to thousands of picoseconds.

Relaxed lower polariton lifetimes are short, around 2.1-2.4 ps, and are largely independent of the Huang-Rhys parameter.

The lifetime extension depends on the exciton/phonon coupling strength.

Abstract

In molecular photochemistry, the non-equilibrium character and subsequent ultrafast relaxation dynamics of photoexcitations near the Franck-Condon region limit the control of their chemical reactivity. We address how to harness strong light-matter coupling in optical microcavities to isolate and preferentially select specific reaction pathways out of the myriad of possibilities present in large-scale complex systems. Using Fermi's Golden Rule and realistic molecular parameters, we estimate the extent to which molecular configurations can be "locked" into non-equilibrium excited state configurations for timescales well beyond their natural relaxation times. For upper polaritons--which are largely excitonic in character, molecular systems can be locked into their ground state geometries for tens to thousands of picoseconds and varies with the strength of the exciton/phonon coupling (Huang-Rhys parameter). On the other hand, relaxed LP lifetimes are nearly uniformly distributed between 2.1-2.4\,ps and are nearly independent of the Huang-Rhys parameter.