FLUORESCENT PROPERTIES OF CATIONIC ANIONIC POLYMETHINE DYES

The fluorescence spectra were studied and the quantum yields of the fluorescence of a number of cationic-anionic polymethine dyes were measured in polar, low-polarity, and nonpolar solvents. It was shown that the fluorescence spectra of cationic - anionic dyes in polar solvents, like the absorption spectra, represent the sum of the fluorescence spectra of the corresponding cationic and anionic dyes. For dyes in which the absorption bands of the anion and cation are close and a new short-wave band arises in the ion pairs, excitation into this band virtually does wt lead to fluorescence, which is a consequence of the forbidden nature of the long-wave transition that arises as a result of the interaction of the chromphores. For a number of cationic-anionic dyes in ion pairs an energy transfer is observed. When an ion possessing short-wave absorption is excited, an ion with long-wave absorption fluoresces.