Intramolecular Phototransfer of Protons and the Quenching of Fluorescence of Derivatives of 2-(Coumarinyl-3)-5-(ortho-hydroxyphenyl)-1,3,4-oxadiazole |
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Authors: | A O Doroshenko E A Posokhov K M Sytnik S N Kovalenko |
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Institution: | (1) V. N. Karazin Kharkov National University, Kharkov, 61077, Ukraine;(2) Ukraine Pharmaceutical Academy, Kharkov, 61001, Ukraine |
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Abstract: | The spectral-luminescence properties of ortho-hydroxy derivatives of 2-(coumarinyl-3)-5-phenyl-1,3,4-oxadiazole have been studied. It is shown that the basic reason for the decreased quantum yield of emission for the compounds studied is the high-speed phototransfer of a proton (estimated as 109 s-1). Fluorescence of the products of this reaction (phototautomers) was not observed. It was confirmed by quantum-chemical calculations that the increase in efficiency of nonradiative dissipation of the electron excitation energy in phototautomeric forms of ortho-hydroxycoumarinyloxadiazoles is explained by an increase in intramolecular donor-acceptor interaction on introduction of the coumarin unit into the molecule. As a result of the high efficiency of nonradiative deactivation of the excited state, the ortho-hydroxyderivatives studied have promise as UV photostabilizers in polymeric materials. |
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Keywords: | 2-(coumarinyl-3)-5-(ortho-hydroxyphenyl)-1 3 4-oxadiazole intramolecular proton transfer extinction of fluorescence |
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