The fluorescence and triplet state quenching of 7-amino-1,3-naphthalenesulfonic acid by paramagnetic metal ions have been investigated in an aqueous medium. The basic mechanism of the fluorescence quenching involves the static and dynamic electron transfer to the paramagnetic cation. The induced S(1)-->T(1) intersystem crossing at fluorescence quenching of the fluorophore by Cu2+ cation has been found. There is a correlation between triplet state quenching rate constants and values of the efficient paramagnetic susceptibility and spin of the cations. The rate constants for the quenching pathways have been calculated.
Neutral quinolyl-and pyridyl-substituted hetarylazoles and their protonated (ethylated) cations with anomalously high Stokes shifts were investigated. Fluorescence measurements at different temperatures and pressures confirmed the viscosity-dependent activation relaxation of the latter. Fluorescence kinetic analyses at various temperatures showed that in the range 293-77 K, the " k k f values of cations increase 2-8-fold whereas those of neutral molecules change only 0.3-1.5-fold. The low-temperature time-resolved emission spectra of 1a, 1H þ and 5a were found to be consistent with the model: A ! A* $ B*, where A* is the local excited planar and B* is the relaxed twisted state of the molecule.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.