The effects of the nature of solvent, temperature and complex formation with alkali and alkaline-earth metal cations, as well as protonation, on the efficiency and the kinetics of fluorescence of 3-azacrowned 7-diethylaminocoumarins have been studied. For the crown-ethers under investigation, the ratio of a dipole moment to the radius of Onsager cavity delta micro/rho is a constant value, and a macrocycle does not affect delta micro, and rho. The fluorescence of coumarin 1 in acetonitrile is quenched by an electron donor, triethylamine, with the Stern-Volmer constant being equal to (0.474+/-0.009) M(-1). The decrease in coumarin 1 fluorescence quantum yield upon the introduction of N-alkylazacrown moiety into position 3 is caused by an intramolecular photoinduced electron transfer from the nitrogen atom of macroheterocycle to the coumarin moiety, where the excitation is localized. The fluorescence quenching has an activation energy 2.32+/-0.05 kcal/mol in various hydrocarbons, and does not depend on the solvent viscosity. The fluorescence kinetics of free crowned coumarins in methanol is not monoexponential because of the existence of macrocycle conformers, or because of the hydrogen bond complex formation between the solvent and the nitrogen atom of macrocycle, in which the efficiency of intramolecular electron transfer is different. Upon complex formation with alkali and alkaline-earth metal cations and upon protonation, the fluorescence quantum yield increases and fluorescence decay becomes monoexponential.

Crown-containing butadienyl dyes containing various heterocyclic moieties and azacrown ether fragments were synthesized for the first time. The spatial structures and the absorption and fluot?escence spectra of crown-containing butadienyl dyes and their complexes with metal cations were examined. The effects of the nature of the heterocyctic and crown ether fragments on fluorescence and generation of dyes and their complexes with metal cations were revealed based on the spectral data.

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A series of DMABN‐related compounds with two‐band fluorescence was studied by steady‐state absorption and fluorescence spectroscopy, time‐resolved absorption spectroscopy upon excitation with a 30‐fs laser pulse, and by TDDFT and xMCQDPT2 quantum chemical methods. The efficiency of the intramolecular electron transfer was found to depend on the excitation wavelength in MeCN. The reaction is described by a two‐state scheme (LE↔CT); the Stevens‐Ban method gives underestimated values for the reaction enthalpy ΔH (SB). The spectral luminescence and kinetic parameters, rate constants, and barriers for the forward (k1, Ea) and reverse (k−1, Ed) electron transfer were calculated. The Marcus plot for k1 versus the driving force (−ΔG) and the total reorganization energy (λ) were calculated for six compounds. It was shown that without a barrier, the 1/k1 value (267 fs) is close to the mean solvation time in MeCN (260 fs), ie, the reaction rate is completely determined by the solvent. The results of conformational analysis for all studied compounds are consistent with the twisted intramolecular charge transfer model of structural relaxation.

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Charge transfer complexes between bis(18-crown-6)stilbene and viologen analogues. A femtosecond study of photoinduced electron transfer.