Vibrational polaritons are hybrid light-matter states arising from the collective strong-coupling of ensembles of localized molecular vibrations and IR modes in a microcavities. Ground-state chemical reactions have been experimentally shown to be modified by vibrational polaritons. Currently available theories seem to be unable to explain these observations. We will describe our most recent progress in the understanding of this puzzle. In particular, we will highlight how cavity versions of transition-state and Marcus theories for chemical kinetics are limited in explaining the experiments. We argue that the underlying problem is the large number of molecules N that partake in the collective strong coupling, yielding an enormous ratio of dark states per polariton mode. We conclude with a potential solution to this problem, which relies on recognizing the conditions under which the many dark states can yield nontrivial chemical dynamics.
Quantum dynamics of the photoisomerization of a single thiacynine iodide molecule embedded in an optical microcavity was theoretically studied. The molecular model consisting of two electronic states and the reaction coordinate was coupled to a single cavity mode via the quantum Rabi Hamiltonian. We show that an electronic excitation of the molecule at cis configuration is followed by the generation of two photons in the trans configuration upon nonadiabatic isomerization. Although conditions for this phenomenon to operate in the collective strong light-matter coupling regime were found to be unfeasible for the present system, our finding suggests a new mechanism that, without ultrastrong coupling, achieves photon down-conversion by exploiting the emergent molecular dynamics arising in polaritonic architectures.
The recent interest on the manipulation of chemical processes within confined electromagnetic environments has opened up new directions on theoretical efforts to rationally design and understand the emergent dynamics of organic molecules embedded in the former.
In this work, we extent the theoretical methodology toolbox to treat these systems by presenting a variational approach applicable to different regimes of vibronic coupling (dynamical disorder) and light-matter couplings for organic molecules. We use this method to understand and predict the influence of coupling of molecular aggregates to photon fields on triplet harvesting. The latter, being a relevant photophysical process for the design of efficient optoelectronic devices, has been recently and experimentally shown to be effectively changed in optical microcavities.
Strong coupling (SC) between light and matter has emerged in the last decade as a promising tool to control room-temperature photophysical processes in organic molecules. In this article, we aim to provide a pedagogical introduction to the various flavors of molecular SC involving (a) a single molecule in an optical nanocavity (e.g. a plasmonic junction), and (b) many molecules in an optical microcavity (the collective regime). Although the linear optical properties of these two systems are very similar, their chemical dynamics are drastically different from each another. We will highlight the relevant timescales and rates that can be manipulated via both flavors of SC. We will illustrate these ideas with theoretical and experimental examples from our previous work, which will help us distill the physical mechanisms that are at play in each SC case.
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