Evidence of Exciton Self-Trapping in Pseudoisocyanine J-Aggregates Formed in Layered Polymer Films

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 FTC 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.