Single particle spectroscopic investigation on the interaction between exciton transition of cyanine dye J-aggregates and localized surface plasmon polarization of gold nanoparticles

The interaction between molecular exciton and localized surface plasmon (LSP) polarization has been investigated by measuring light scattering spectra of single gold nanoparticles coated with cyanine dye J-aggregate. The spectral dip reflecting absorption spectral band of the J-aggregate varies with the particle size and the distance between the J-aggregates and the surface of gold nanoparticles. By comparing the experimental results with theoretical calculations based on the Mie theory, we demonstrate that the LSP polarization affects the peak and shape of the J-aggregate absorption band when the exciton resonance peak locates near the LSP resonance peak and when the separation of the J-aggregate from the metal surafce is short. The modification of the J-aggregate exciton band induced by LSP is considered to be due to strong coupling between the molecular exciton transition and the LSP resonance of metallic nanoparticles.