Identifying\nDifferences between Semiclassical and\nFull-Quantum Descriptions of Plexcitons

Strong light–matter coupling between molecules\nand plasmonic\nnanoparticles gives rise to new hybrid eigenstates of the coupled\nsystem, commonly referred to as polaritons or, more precisely, plexcitons.\nOver the past decade, it has been amply shown that molecular electron\ndynamics and photophysics can be drastically affected by such interactions,\nthus paving the way for light-induced control of molecular excited\nstate properties and reactivity. Here, by combining the ab initio\nmolecular description and classical or quantum modeling of arbitrarily\nshaped plasmonic nanostructures within the stochastic Schrödinger\nequation, we present two approaches, one semiclassical and one full-quantum,\nto follow in real time the electronic dynamics of plexcitons while\nrealistically taking plasmonic dissipative losses into account. The\nfull-quantum theory is compared with the semiclassical analogue under\ndifferent interaction regimes, showing (numerically and theoretically)\nthat even in the weak-field and weak-coupling limit a small-yet-observable\ndifference arises.