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.

Optical spectroscopy experiments were used to study the features of cyanine dye 3,3'-dimethyl-9-(2-thienyl)-thiacarbocyanine iodide (L-21) aggregation in binary solutions DMF:Tris-HCl buffer (pH = 8) containing nucleic acids (DNA or RNA). The appearance of absorption and luminescence bands associated with J-aggregates and dimers that are formed within the minor groove of DNA has been observed. The model of L-21 J-aggregate structure is proposed. It has been found that dimers are the building blocks of L-21 J-aggregates. Disorientation in dimers caused by the minor groove curvature is reason of observation of Davydov splitting in absorption spectrum of L-21 J-aggregates. In the solution containing DNA the absorption and luminescence bands of L-21 J-aggregates exhibit the specific properties that allows the dye L-21 to be used as a fluorescent probe for DNA detection.

Using fluorescent microscopy and microspectroscopy, optical properties and morphology transformations in individual pseudoisocyanine (PIC) J-aggregates in aqueous electrolyte solutions have been explored. A stringlike structure of J-aggregates with a string diameter much less than 1 μm has been observed. Photodestruction of the strings under short-wavelength excitation has been revealed. Rodlike PIC crystallites, about 1 μm in diameter, have been observed with time. The fluorescence spectrum of rodlike crystallites has been found to differ from that of stringlike J-aggregate and from PIC crystal powder spectra. The crystallites are very stable, and their photodestruction has not been observed under any excitation conditions. It has been found that rodlike crystallites in contrast to stringlike J-aggregates possess optical waveguide properties. The luminescence of crystallites can be observed only at the excitation spot and at butt ends located up to hundreds of micrometers from the excitation spot.