The optical properties of a nanoparticle dimer bridged by a conductive junction depend strongly on the junction conductivity. As the conductivity increases, the bonding dimer plasmon blueshifts and broadens. For large conductance, a low energy charge transfer plasmon also appears in the spectra with a line width that decreases with increasing conductance. A simple physical model for the understanding of the spectral feature is presented. Our finding of a strong influence of junction conductivity on the optical spectrum suggests that plasmonic cavities might serve as probes of molecular conductance at elevated frequencies not accessible through electrical measurements.

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We present a theoretical study of the optical properties of a strongly coupled metallic dimer when an ensemble of molecules is placed in the inter-particle cavity. The linking molecules are characterized by an excitonic transition which couples to the Bonding Dimer Plasmon (BDP) and the Bonding Quadrupolar Plasmon (BQP) resonances, arising from the hybridization of the dipolar and quadrupolar modes of the individual nanoparticles, respectively. As a consequence, both modes split into two coupled plasmon-exciton modes, so called plexcitons. The Charge Transfer Plasmon (CTP) resonance, involving plasmonic oscillations of the dimer as a whole, arises when the conductance of the excitonic junction is above a threshold value. The possibility of exploiting plexcitonic resonances for sensing is explored in detail. We find high sensitivity to the environment when different dielectric embedding media are considered. Contrary to standard methods, we propose a new framework for effective sensing based on the relative intensity of plexcitonic peaks.

We present a theoretical study of a metal-molecular aggregate hybrid system consisting of a strongly coupled dimer connected by molecules characterized by an excitonic transition. The plasmonic resonances of the metallic dimer interact with the molecular excitations giving rise to coupled plasmon-exciton states, so called plexcitons. We compare the differences in the optical response when the excitonic material is placed only as a linker in the plasmonic gap of the dimer and when the material is distributed as an aggregate layer covering the dimer entirely. We also explore the efficiency of plexcitons for localized surface plamon resonance (LSPR) sensing in both situations. The ordinary shift-based sensing is more efficient for dimers connected through molecular linkers, whereas intensity-based sensing is more effective when the molecular aggregate covers the entire nanostructure. These results can serve to design the chemistry of excitons around metallic nanoparticles.

In this work we study how plasmon modes of gold dimers are affected by a molecular bridge connecting both particles. Different models for the linker are considered to envisage the relation between the spectral changes observed in the extinction spectra and the electronic transport through the molecules. Depending on the size and nature of the molecular linker two different modes, known as BDP (Bonding Dimer Plasmon) and CTP (Charge Transfer Plasmon), are excited. Furthermore, when the molecular linker has an excitonic resonance, new spectral features emerge due to the plasmon-exciton coupling.