Optical properties of hybrid film depending on overlap of the nanoparticle plasmon resonance and J-aggregate band of cyanine dye

Abstract

The hybrid systems consisting of noble metal nanoparticles with plasmon resonances and organic cyanine dye, which are able to delocalize and migrate the energy of excitons on a large number of aggregated molecules of the structure, can be used to study the plasmon-exciton interaction. The position as well as the region of overlap of the absorption of the exciton band and the plasmon resonance of the nanoparticles in the form of island film allows observing both weak and strong coupling. The influence of overlap between the J-aggregate band of cyanine dyes with different length of the conjugation chain and nanoparticle plasmon resonance on the optical properties of hybrid structures was studied. Inhomogeneous ensembles of noble nanoparticles were obtained as an island films on the sapphire substrates by thermal deposition in vacuum. The homologous series of dicarbocyanine, monocarbocyanine and pseudoisocyanine dyes was used for forming J-aggregates in ethanol solution without adding salt by the original technique. Dye solution was spincoated on the island film to obtained hybrid structure. The plasmon resonance of the island film was broadened due to the large dispersion of the nanoparticles in size. So strong and weak plasmon-exciton coupling can be observed in hybrid structures due to overlap of the absorption bands of island film and exciton-transition in J-aggregates. The influence of near field of noble nanoparticles on enhancement of dye molecule absorption is observed in hybrid films with dicarbocyanine and monocarbocyanine. The surface molecular concentration was monitored, in the experiment there was no significant increase of the number of adsorbed molecules on island film in comparison with clean dielectric substrate. Spectral dip at the wavelength of the maximum absorption of the J-aggregate was observed for hybrid films with pseudoisocyanine.