FLUORESCENT PROPERTIES OF CATIONIC ANIONIC POLYMETHINE DYES

The fluorescence spectra were studied and the quantum yields of the fl uorescence of a number of cationic-anionic polymethine dyes were measu red in polar, low-polarity, and nonpolar solvents. It was shown that t he fluorescence spectra of cationic - anionic dyes in polar solvents, like the absorption spectra, represent the sum of the fluorescence spe ctra of the corresponding cationic and anionic dyes. For dyes in which the absorption bands of the anion and cation are close and a new shor t-wave band arises in the ion pairs, excitation into this band virtual ly does wt lead to fluorescence, which is a consequence of the forbidd en nature of the long-wave transition that arises as a result of the i nteraction of the chromphores. For a number of cationic-anionic dyes i n ion pairs an energy transfer is observed. When an ion possessing sho rt-wave absorption is excited, an ion with long-wave absorption fluore sces.