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Organic dyes are very promising substrates for modern sensing technologies. Their utility is based on the ‘push-pull’ polarization of a π-electron system, as well as their polyfunctionality. These properties make organic dyes capable of fluorescent sensory response to many analytes and provide different mechanisms of both fluorescence increase and fluorescence quenching. Specific organic reactions and structural transformations of fluorescent organic dyes are under consideration in this review. The data confirming the structures of the products of the related analytical reactions are discussed in more detail. Knowledge of the transformations that fluorescent organic dyes undergo in sensory effects can contribute to successful design of specific probes for novel sensory technologies. The bibliography includes 365 references.

New (1,5-diaryl-3-pyrazolinyl)coumarins have been synthesized. The compounds do not undergo keto-enol tautomeric transformations with changes in the solvent. (1,5-Diaryl-3-pyrazolinyl)coumarins provide dehydrogenation reaction under irradiation in the presence of perchloroalkanes and manifest themselves as effective photogenerators of acidity. Several aspects of photodehydrogenation mechanism have been studied. Oxygen is shown not be involved in the reaction. Polar solvents increase rate of the reaction. The measured rate constants of the photodehydrogenation reactions vary in a significant range according to the structure of pyrazoline. The data correlate with ionization potentials of pyrazolines available from DFT quantum chemical calculations. These results are discussed in terms of proposed scheme of mechanism of pyrazolines photodehydrogenation assuming formation of ion-radical and ion intermediates.

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