A Theoretical Perspective on Molecular Polaritonics

Abstract

In the past decade, much theoretical research has focused on studying the strong coupling between organic molecules (or quantum emitters, in general) and light modes. The description and prediction of polaritonic phenomena emerging in this light−matter interaction regime have proven to be difficult tasks. The challenge originates from the enormous number of degrees of freedom that need to be taken into account, both in the organic molecules and in their photonic environment. On one hand, the accurate treatment of the vibrational spectrum of the former is key, and simplified quantum models are not valid in many cases. On the other hand, most photonic setups have complex geometric and material characteristics, with the result that photon fields corresponding to more than just a single electromagnetic mode contribute to the light−matter interaction in these platforms. Moreover, loss and dissipation, in the form of absorption or radiation, must also be included in the theoretical description of polaritons. Here, we review and offer our own perspective on some of the work recently done in the modeling of interacting molecular and optical states with increasing complexity.

Theoretical Advances in Polariton Chemistry and Molecular Cavity Quantum Electrodynamics

“…There are two overall regimes of light–matter coupling which offer different mechanisms for changing chemical reactivity: the weak coupling and the strong coupling regimes. The primary characteristic that differentiates these two regimes is whether the light–matter coupling strength g c is smaller than (weak coupling) or larger than (strong coupling) the various loss rates of the system. − In the weak coupling regime, the primary mechanism for modifying chemistry is through an enhancement of the overall loss rate of the system, known as the Purcell effect. ,, In this regime, there is a limited modification of the potential energy surfaces which limits the amount of control one has over modifying chemical reactions. On the other hand, in the strong coupling regime, significant changes to the potential energy surfaces can be observed and are adjustable based on fundamental physical characteristics such as the cavity frequency ω c and the light–matter coupling strength g c .…”

Quantitative Investigation of the Rate of Intersystem Crossing in the Strong Exciton–Photon Coupling Regime

“…These molecular localized optically inactive states have an energy envelope resembling that of the bare molecular transition (S 1 ). Although the relaxation dynamics in strongly coupled systems is heavily dominated by processes going through the exciton reservoir, it is not clear if it always governs excited-state relaxation efficiencies. ,,− …”

Effective Single-Mode Methodology for Strongly Coupled Multimode Molecular-Plasmon Nanosystems

“…Strong light–matter coupling between molecules and electromagnetic fields leads to the formation of new hybrid states, known as polaritons, where the quantum nature of the electromagnetic field entangles with purely molecular states. − The resulting polaritons can display different key features compared to the original states, potentially leading to new chemical/photochemical reactivity, ,− energy transfer processes, − or relaxation channels, ,− among others. While photonic cavities are an obvious choice, other fields, like the ones produced by electronic excitations in plasmonic nanostructure, can also be used to achieve the strong coupling regime.…”