Polarization-Resolved Spectral Features and Dielectric Medium Effects in Plexcitonic Systems: Findings from Single-Particle Spectroscopy

Strong coupling between plasmonic and excitonic systems creates new hybrid states comprising upper (E⁺) and lower (E^–) plexcitonic bands. On-demand switching of these bands holds potential for applications in next-generation optoelectronic devices. Plexcitonic nanostructures are obtained herein by electrostatically binding J-aggregates of 1,1′-diethyl-2,2′-cyanine iodide onto gold nanorods that are coated with silver shell. To avoid ensemble averaging effects, single-particle spectroscopy is employed allowing the collection of scattering spectra from individual nanostructures as a function of refractive index of the medium and the polarization angles of the light. Both experimental and finite-difference time-domain simulation studies revealed a gradual increase in the intensity of the E^– band and a decrease in that of the E⁺ band, as the refractive index of the medium increased from 1.0 to 1.5. In contrast, on varying the polarization angle, a gradual disappearance and formation of both the plexcitonic bands are observed.