Colloidal silver (Ag) and gold (Au) nanoparticles are functionalized with organic dye molecules in order to engineer strong plasmon-exciton or “plexcitonic” interactions across the entire visible wavelength range (400-800 nm). In the case of Ag, spherical nanoparticles of varying diameter are chemically bonded to fluorescein isothiocyanite (FITC), and in the case of Au, nanorods of varying aspect ratio are electrostatically bonded to one of two forms of cyanine (Cy+ or CCy+). The dyes in question can bind as monomers or in aggregated forms to the nanoparticles. Particularly strong interactions are found in Ag-FITC systems that correspond to monomeric FITC molecules surrounding the Ag nanoparticles and in Au-Cy+ systems where the Cy+ molecules form J-aggregates covering the Au nanorods. These strong interactions can be correlated with large oscillator strengths and narrow spectral widths in the corresponding dye systems. By varying the diameter or aspect ratio, the plasmon resonance energy (or wavelength) inferred from extinction spectra of uncomplexed particles can be systematically varied and pass through the dye resonance energy. Extinction spectra of the hybrid systems can display large Rabi splittings and we are able to map out dispersion curves. Simple quantum and classical models allow us to infer plexcitonic coupling energies that are quite large (~ 200 meV for Ag-FITC and ~100 meV for Au-Cy+) and approaching the strong coupling limit.

Strong plexcitonic interactions in colloidal solutions containing hybrid metal nanoparticle/dye systems

254th National Meeting (2017)

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