Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations.

Area of Science:

• Physical Chemistry
• Quantum Optics
• Materials Science

Background:

• Strong light-matter coupling forms polaritons, hybrid states of molecules and cavity photons.
• Polaritons modify molecular potential energy surfaces, offering control over photochemistry.
• Sufficient polariton lifetime is essential for reactions to occur on modified surfaces.

Purpose of the Study:

• Investigate factors limiting polariton lifetimes in optical cavities.
• Understand population transfer dynamics between polaritons and dark states.
• Inform strategies for enhancing polaritonic chemistry control.

Main Methods:

• Atomistic molecular dynamics simulations.
• Room-temperature ensembles of rhodamine chromophores.
• Strong coupling to a single confined light mode (15 fs lifetime).
• Optical pumping of lower polariton, upper polariton, and molecular states.

Main Results:

• Polariton lifetimes limited by ultrafast photoemission and reversible dark state transfer.
• Dark state population transfer depends on spectral overlap between polaritonic and molecular absorption.
• Upward excitation transfer from lower polaritons to dark states observed, challenging one-way relaxation models.

Conclusions:

• Effective polaritonic chemistry requires long cavity lifetimes and strong light-matter coupling.
• Preventing excitation back-transfer to dark states is critical for sustained polaritonic control.
• Understanding polariton-dark state dynamics is key to harnessing polaritonic effects in photochemistry.