STUDY OF FLUORESCENT AGGREGATES OF POLYMETHINE DYES

Absorption, fluorescence, and fluorescence excitation spectra have bee n studied for a number of anionic, cationic, and cationic-anionic poly methine dyes in low-polar and nonpolar solvents, as well as in binary mixtures of solvents differing in polarity. For most of the dyes studi ed, fluorescent aggregates have been found to form. Their broad fluore scence bands are located in the long-wave region with respect to those of the initial dyes. The quantum yield of the aggregate fluorescence is normally higher than that of the initial dyes. Fluorescence excitat ion spectra of some cationic-anionic dyes in nonpolar solvents disagre e with their absorption spectra because of contact and solvent-separat ed ion pairs simultaneously present in the solution.