Optical properties of molecular clusters of cyanine dyes on Ag and Au island films

Abstract

Organic nanoclusters, so-called J-aggregates, composed of cyanine dyes possess properties different from constituting molecules. There is a growing interest in the study of organic dyes conjugates with metal nanoparticles. The combination of unique properties of J-aggregates and plasmonic nanoparticles allow novel effects to be observed in such systems. The optical properties of molecular layer of cyanine dyes and its J-aggregates, coated on the island films in the form of a heterogeneous ensemble of silver or gold nanoparticles, were studied by absorption and fluorescent spectroscopy, as well as AFM. The original method for obtaining cyanine J-aggregates on metallic films without use of salt and water was developed. The molecular nanoclusters obtained on silver island film were stable for a week, while aggregation of cyanine molecules was much smaller on gold island films. The absorption spectrum of the organometallic film is not a simple sum of the spectra of its components. The absorption of dye molecules increases several times in the presence of silver nanoparticles in comparison with gold island film. Besides, the induced transparency is observed at the absorption maximum of J-aggregates, which can indicate the interaction between the plasmons of metal nanoparticles and the excitons of the J-aggregate.