Modified excited states dynamics in the nanoparticle plasmon – molecular exciton hybrids under strong coupling regime

Strong light-matter interactions in microcavities have been long known to provide means to alter optical and nonlinear properties of the coupled system. As a result of this interaction, one typically observes the emergence of new polaritonic eigenstates. These states are of hybrid nature and possess both light and matter characteristics, which is reflected in vacuum Rabi splitting, observed in the absorption or transmission spectra. Because of the hybrid nature of these states, the excited state temporal dynamics can be significantly altered in comparison to the uncoupled system dynamics. This, in turn, can have profound effects on the emission and photochemical processes.
Here, we show that individual plasmonic nanoantennas can strongly couple to molecular J-aggregates, resulting in splitting up to 400 meV, i.e. ~20% of the resonance energy. Moreover, we observe mode splitting not only in elastic scattering response but also in photoluminescence of individual hybrid nanosystems, which manifests a direct proof of strong coupling in plasmon-exciton nanoparticles. This situation is drastically different from the photoluminescence of uncoupled molecules, which signals the involvement of polaritonic states into the relaxation pathways of the hybrid system. We also discuss how the involvement of these pathways can modify excited state dynamics, including such important photochemical processes as photobleaching.