At low temperatures in the luminescence spectrum of pseudoisocyanine (PIC) J-aggregates formed in a layered polymer film an unusual broad red-shifted band appears. The analysis of spectral properties of PIC J-aggregates allowed us to ascribe the additional red band to the exciton self-trapped state. In a layered polymer film, PIC J-aggregates are found to possess a 2D island-like structure, which results in a barrier type of the exciton self-trapping with coexisting free and self-trapped excitons. Both the strong topological disorder and exciton−phonon coupling are suggested to be the reason for the exciton self-trapping in J-aggregates. Nonradiative relaxation of self-trapped excitons at room temperature has been proposed to be responsible for a very low luminescence quantum yield and giant nonradiative rate constant for PIC J-aggregates formed in a layered film.

Features of plasmon-enhanced fluorescence in pseudoisocyanine (PIC) J-aggregates formed in polyelectrolyte films at liquid nitrogen temperature have been studied. Due to efficient exciton self-trapping in polymer-bound PIC Jaggregates, their fluorescence spectra consist of two well-separated bands: a narrow near-resonant band belonging to free excitons and a wide red-shifted band assigned to self-trapped excitons. It has been found that in hybrid complexes composed of polymer-bound J-aggregates and gold nanoparticles placed on some optimal distance from J-aggregates, the interaction with plasmon resonance of gold nanoparticles leads to an increase in free-exciton fluorescence, whereas self-trapped exciton emission slightly decreases. Suppression of exciton self-trapping due to plasmon-induced enhancement of the exciton coherence length has been supposed and confirmed by a 2-fold decrease in the exciton−phonon coupling constant.

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