Kinetics of the rearrangement of the solvation shell of an excited fluorescent probe 4″-dimethylaminochalcone |
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Authors: | G E Dobretsov S K Gularyan O M Sarkisov F E Gostev A N Petrukhin A A Titov V Yu Svetlichny T I Syrejshchikova |
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Institution: | (1) Research Institute of Physicochemical Medicine, Ministry of Health of the Russian Federation, Moscow, 119992, Russia;(2) Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, 119991, Russia;(3) Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 119991, Russia |
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Abstract: | A study was made of the processes associated with the quenching of 4″-dimethylaminochalcone (DMAC) fluorescence by proton-donor solvent (1-butanol). The kinetics of deactivation of the DMAC excited state was assessed by transient absorption spectra with a time resolution about 50 fs and by fluorescence decay with ~30-ps resolution. The following sequence of events could thus be envisaged: (i) the DMAC molecule in the ground state (prior to excitation) makes a hydrogen bond with an alcohol molecule; (ii) absorption of a light quantum causes a corresponding increase of the DMAC dipole moment; the H-bond is retained; (iii) the solvation shell formed by alcohol dipoles is reorganized in response to the raise of the DMAC dipole moment, with an energy expenditure about 24 kJ/mol and a time constant about 40 ps; the initial H-bond is still retained; (iv) processes leading to fluorescence quenching occur with an effective time constant of nearly 200 ps. Since quenching is far slower than solvate rearrangement, one can suppose that it is not a direct consequence of shell relaxation or prior H-bonding. Thus, DMAC fluorescence quenching may involve different processes observed with other aromatic molecules: H-bond rearrangement from a nonquenching to a more ‘efficient’ conformation, charge transfer between the excited molecule and alcohol, or solvent-induced out-of-plane twist of the DMAC amino group. |
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Keywords: | fluorescent probe 4″ -dimethylaminochalcone excited state fluorescence quenching hydrogen bond solvation shell relaxation |
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