Modeling Hybrid Nanosystems of Interacting Molecules and Plasmonic Nanoparticles

Strong light-matter coupling provides a clean and effective means to modify the accessible energy landscapes of molecular species, impacting both spectroscopic observables and chemical reactivity. Beyond optical cavities, localized plasmonic modes supported by noble metal nanostructures have become widely used in this field. The ability to tune and exploit the resulting light-matter hybrid states (polaritons, or more precisely, plexcitons) for manipulating molecular properties and behavior has sparked the flourishing area of Polaritonic Chemistry. This thesis focuses on modeling complex systems of molecules and plasmonic nanoparticles, characterized by multiple interactions between the constituent species. The most distinctive feature is the coupling of molecular (electronic) excitations with plasmonic modes, enabling the mixing of plasmonic and molecular characters in the resulting hybrid eigenstates. Since many molecules, relatively close to each other, can be collectively coupled to the same plasmon, intermolecular interactions must also be considered. A novel, state-of-the-art strategy was developed to evaluate molecule-plasmon coupling for each individual dye. This strategy was applied to both well-known nanohybrids and molecular substrates that had not yet been examined for polaritonic applications. For the well-known nanohybrids, the results confirmed that the implemented extensions, compared to standard quantum optics models, not only allowed for more refined and realistic modeling but also provided valuable insights for guiding the interpretation of available experimental data and directing the design of further investigations. These insights included the inhomogeneous contributions within a molecular assembly collectively coupled to the same plasmon mode and the intermixing of spectral branches that are well-separated for the isolated chromophore. For the molecular substrates not previously examined for polaritonic applications, a thorough investigation of the relevant excited states revealed a highly dynamic scenario. This finding paves the way for ongoing explorations of the impact of interactions with tailored plasmonic platforms.