Plasmon Controlled Exciton Fluorescence of Molecular Aggregates

Abstract

In the present work controlled plasmon enhanced fluorescence of thiacyanine dye J-aggregates in water solution has been demonstrated. To control a distance between J-aggregates and silver nanoparticles the latter have been covered by a polymer shell of variable thickness using the layer-by-layer assembly method. The best 2-fold fluorescence enhancement has been observed for the 16 nm thick polymer shell. Transmission electron microscopy (TEM) images have revealed an insufficient contact between J-aggregates and NPs that could be the main reason for the small fluorescence enhancement. Experimental results have been described using a model of two-level system affected by the local plasmon resonances field. According to the model more than 20-fold enhancement of J-aggregates fluorescence could be expected under optimal conditions. Besides, strong fluorescence enhancement dependence on an exciton coherence length has been predicted. According to it, significant fluorescence response should be observed for metal nanoparticles interacting J-aggregates with large exciton coherence length such as pseudoisocyanine J-aggregates and some others.