Coherent Mechanism of Exciton Transport in Disordered J-Aggregates

Using a luminescent exciton trap, a mechanism of the exciton migration in disordered J-aggregates of amphiphilic analogue of pseudoisocyanine (amphi-PIC) dye has been investigated in the temperature range of 80−300 K. Due to a strong topological disorder in amphi-PIC J-aggregates observed in a binary dimethylformamide−water (DMF/W) solution with a low water content, two types of excitonic states have been revealed, delocalized exciton state that forms the main part of the J-aggregates absorption band (J-band) and a state of strongly localized excitons that forms the long-wavelength edge of the J-band. These excitonic states are characterized by the different mechanism of the exciton transport: a coherent mechanism for delocalized excitons and an incoherent one for localized excitons. As localized excitons provide a small contribution to the J-band and appear only at high degree of topological disorder, the coherent mechanism of the exciton transport in amphi-PIC J-aggregates has been concluded. Such a result is nontrivial due to a small delocalization length of excitons in amphi-PIC J-aggregates (11 monomers at 80 K) provided by the moderate energetic disorder and strong exciton−phonon coupling.