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Prospects for analytical application of 2,5-diphenyloxazole-substituted 3-hydroxychromone for detection of mercury ions are presented. Sensitivity and selectivity for a number of metal ions both in methanol solution and in the plasticized polymer are outlined. Ultrasensitive and highly selective fluorescent ratiometric response of the polymer film containing the title compound for mercury ions in water media is revealed. Reversibility of ratiometric response to mercury ions and influence of plasticizer’s content in the polymer film on the optical feedback are also discussed. [...]
Three 2-(benzimidazol-2-yl)-3-hydroxychromone derivatives were synthesized. Their spectroscopic and fluorescent properties, due to excited state intramolecular proton transfer (ESIPT) from OH to carbonyl, were studied. Theoretical possibility of an alternative intramolecular H-bonding and experimental evidence for such behavior are discussed. [...]
Synthesis and systematic investigation of the spectral-luminescent properties of “bis-flavonol” {1,4-bis-(3-hydroxy-4-oxo-4H-chromen-2-yl)-benzene} were performed. Hypothetical possibility for the double excited-state proton transfer reaction in bis-flavonol is discussed based on both quantum-chemical modeling and experimental data. Consecutive S1*-state transfer of the two protons of the title molecule is shown to be energetically unfavorable, however, still preserving a possibility for the concerted double proton transfer in the excited dienol form.
Unique properties of a new 3-hydroxychromone derivative 2-(6-diethylaminobenzo[ b]furan-2-yl)-3-hydroxychromone (FA) in its ability to exhibit excited-state intramolecular proton transfer (ESIPT) reaction are described. In contrast to all other chromone and flavone derivatives studied, in low-polar solvents it exhibits in emission, together with the tautomer (T*) band, an intensive band of the normal (N*) form. Previously the intensive N* form in emission was observed only in highly polar, mostly protic solvents. While its absorption spectra are sensitive to H-bond acceptor properties of the solvent, the fluorescence spectra are not. This suggests that intermolecular H-bonds with a solvent, if they exist in the ground state, are reorganized in the excited state in favor of intramolecular bond, which is the pathway for ESIPT reaction. The energy difference, _N* - _T*, between N* and T* emission maxima is in almost ideal correlation with the Reichardt solvatochromic parameter EN T . This suggests the use of FAas a highly sensitive polarity sensor.Agood correlation between _N* - _T*, and the ratio of the N* and T* band intensities is observed. This allows to observe the solvent effects on a manifold increased level of sensitivity. The analysis based on Lippert and Bakhshiev equations and the quantum- chemical calculations suggest a substantial increase of the dipole moment on electronic excitation to the N* state. The appearance of the N* form in emission may be the result of its dielectric stabilization.
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