Cooperative Chemical Reactions in Optical Cavities: A Complex Interplay of Mode Hybridization, Timescale Balance, and Pathway Interference

TL;DR

The paper addresses how strong light–matter coupling in optical cavities alters chemical reaction rates in condensed phases, with a focus on cooperative and environment-sensitive effects. It develops a numerically exact quantum-dynamical framework based on hierarchical equations of motion (HEOM) in a twin-space formulation, augmented by tree tensor network states (TTNS), to simulate models with $N_{ m mol}$ reactive coordinates and $N_{ m nor}$ spectator modes coupled to a single cavity, plus dissipative baths. The key findings show that cavity-modified reactivity arises from mode hybridization, balanced energy-transfer timescales, and quantum interference between cavity-assisted and intrinsic pathways, producing resonant enhancement, suppression, and asymmetric Fano-type lineshapes; collective coupling further yields rich, parameter-sensitive behavior. These results provide a mechanistic framework for predicting and designing cavity-controlled chemistry and motivate future experiments in few-molecule polaritonic systems to test interference- and collectivity-driven reactivity control.

Abstract

Harnessing strong light-matter interactions to control chemical reactions in confined electromagnetic fields offers a promising route toward deepening our understanding of chemical dynamics at the collective quantum-mechanical level, with potential implications for future chemical synthesis paradigms. Achieving this goal, however, requires an in-depth mechanistic understanding of the underlying dynamical processes. As a step in this direction, we present a systematic and numerically exact quantum dynamical study of cooperative reaction dynamics inside an optical microcavity. Using a hierarchy of model systems with increasing complexity, we elucidate how cavity-modified reactivity emerges from-and is highly sensitive to-subtle structural and environmental variations. Our models consist of optically dark reactive molecules, each represented by a symmetric double well potential, coupled to infrared-active non-reactive intramolecular or solvent vibrational modes, as well as their respective dissipative environments. Our results demonstrate that cavity-induced rate modifications arise from a delicate interplay among mode hybridization in strong-coupling regimes, the dynamical balance of all participating energy exchange processes, and quantum interference between multiple fluctuation-dissipation-mediated reaction pathways enabled by collective cavity coupling. By continuously tuning a single system parameter or introducing molecular collectivity, we observe qualitatively distinct rate modification profiles as functions of the cavity frequency, including resonant rate enhancement, resonant rate suppression, hybridization-induced peak splitting, and, notably, asymmetric Fano-type line shapes in which enhancement peaks and suppression dips coexist within a narrow resonance window, highlighting the important role of quantum interference in cavity-modified chemical reactivity.

Figures (13)

• Figure 1: Schematic illustration of a model system with a single reactive mode ($N_{\rm mol}=1$) interacting with a single non-reactive vibration ($N_{\rm nor}=1$ outside the cavity, together with a graphic representation of the TTNS decomposition of the extended wave function $|\Psi(t)\rangle$ for this scenario.
• Figure 2: Contour plots of the reaction rate $k_{\rm o}$ for the model illustrated in Fig. \ref{['fig:Nmol1Nnor1_model']}, shown as functions of the coupling strength $\eta_{\rm nor}$ and the dissipation strength $\lambda_{\rm nor}$ for two different characterisitic bath frequencies $\Omega_{\rm nor}$. The frequency of the non-reactive vibrationa is fixed at $\omega_{\mathrm{nor}}=1185\,\mathrm{cm}^{-1}$.
• Figure 3: Schematic illustration of a dissipation-free non-reactive vibrational mode bridging a single reactive molecule and a cavity mode, together with the TTNS representation of the extended wave function $|\Psi(t)\rangle$.
• Figure 4: Contour plots of the rate modification ratio $k_{\rm c}/k_{\rm o}$ as functions of the non-reactive vibrational frequency $\omega_{\rm nor}$ and the caivty frequency $\omega_{\rm c}$ for the model system illustrated in Fig. \ref{['fig:Nmol1Nnor1_IC_model']}. Each panel corresponds to a different set of coupling strengths $\eta_{\rm c}$ and $\eta_{\rm nor}$. Other parameters are fixed at $\lambda_{\rm c}=200\,\mathrm{cm}^{-1}$, and $\Omega_{\rm c}=1000\,\mathrm{cm}^{-1}$.
• Figure 5: Contour plots of the rate ratio inside and outside the cavity, $k_{\rm c}/k_{\rm o}$, as functions of the light-matter coupling strength $\eta_{\rm c}$ and the cavity lossy strength $\lambda_{\rm c}$ for the model system illustrated in Fig. \ref{['fig:Nmol1Nnor1_IC_model']}. Different values of the vibrational coupling strength $\eta_{\rm nor}$ are shown in different panels. The frequencies of the cavity mode and the non-reactive harmonic mode are fixed at $\omega_{\mathrm{c}}=\omega_{\mathrm{nor}}=1185\,\mathrm{cm}^{-1}$, and the cavity bath cutoff frequency is set to $\Omega_{\mathrm{c}}=1000\,\mathrm{cm}^{-1}$.