Polarization-Resolved\nSpectral Features and Dielectric\nMedium Effects in Plexcitonic Systems: Findings from Single-Particle\nSpectroscopy

Strong\ncoupling between plasmonic and excitonic systems creates\nnew hybrid states comprising upper (E<sup>+</sup>) and lower (E<sup>–</sup>) plexcitonic bands. On-demand switching of these bands\nholds potential for applications in next-generation optoelectronic\ndevices. Plexcitonic nanostructures are obtained herein by electrostatically\nbinding J-aggregates of 1,1′-diethyl-2,2′-cyanine iodide\nonto gold nanorods that are coated with silver shell. To avoid ensemble\naveraging effects, single-particle spectroscopy is employed allowing\nthe collection of scattering spectra from individual nanostructures\nas a function of refractive index of the medium and the polarization\nangles of the light. Both experimental and finite-difference time-domain\nsimulation studies revealed a gradual increase in the intensity of\nthe E<sup>–</sup> band and a decrease in that of the E<sup>+</sup> band, as the refractive index of the medium increased from\n1.0 to 1.5. In contrast, on varying the polarization angle, a gradual\ndisappearance and formation of both the plexcitonic bands are observed.