Revealing the Interplay between Hybrid and Charge-Transfer States in Polariton Chemistry

Polariton chemistry, otherwise named molecular polaritonics, is a very recent research field exploiting the effects of strong coupling interaction on the chemistry of an emitter, which presents a huge plethora of applications in life sciences, going from in vivo optostimulation to photopharmacology. In this work, we propose for the first time a fully atomistic computational study within the framework of time-dependent density functional theory of a selected direction on the potential energy surfaces of the first electronic states of an azobenzene photoswitch interacting with a tetrahedral Ag-20 nanocluster able to sustain a localized surface plasmon in the spectral range of its isomerization barrier. The idea is to analyze all of the effects of the plasmonic excitation on the excited states of the molecule for the chosen isomers in order to find out, at least for the analyzed isomerization pathway, possible consequences of the presence of the metallic cluster. We present a novel way to investigate the nature of collective excitations which seems to be extremely useful in bringing to light all charge-transfer excitations present in the photodynamics range otherwise not detectable, these being dark modes. Charge-transfer excitations appear along the entire transformation pathway (from trans to cis) chosen in this case; their role is discussed. Ab initio studies like the present one open the way for further theoretical insights as well as real technological achievements in this promising frontier of polariton chemistry.