首页|Spectroscopy study of dimerization of fluorone dyes in AOT reverse micelles
Spectroscopy study of dimerization of fluorone dyes in AOT reverse micelles
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NSTL
Elsevier
The dimerization processes and its thermodynamic parameters of fluoronic dyes (fluorescein (F), eosin (E), erythrosine (ER), bengal rose (BR)) in reverse micelles of AOT with different hydrodynamic radius Rh are studied. The dimerization constants and its efficiency (the degree of dimerization of dye molecules (1-X)) were determined from the experimental data. It is found that an increase in the intercombination conversion due to the heavy atom effect leads to an increase of the value of (1-X). At the same time, the heavy atom effect affects the dye dimerization process for all the studied values of R-h. The linear dependence of (1-X) on Rh is observed. The slope of this dependence is affected by both the mass of the internal heavy atom and the charge of the anionic forms of dyes. It was found that there is a different structure of dye dimers for different R-h for all the studied systems different angles alpha between the molecules in the dimer. A linear dependence of a on Rh is observed. At the same time, the growth gradients alpha(R-h) practically do not differ for F, E, and BR and they are of the greatest importance for the studied water-micellar solutions of dyes. The growth of a from Rh is insignificant for ER. The thermodynamic parameters (such as Gibbs potential DG, enthalpy DH and entropy DS) were calculated from the experimentally measured dependences of the dimerization constant on the temperature. Delta H < 0 and Delta S < 0 in micellar solutions of the studied dyes at all values of Rh, that indicates that the dimerization reaction in the studied systems is controlled by enthalpy. The obtained linear relation ship between TDS and DH indicates the existence of enthalpy-entropy compensation in the dimeric reactions of the molecules of the studied dyes. The linear correlation observed between the values of TDS and DH allowed us to establish that the higher the molecular weight of the halogen in the dye molecule, the more effectively an increase in DH contributes to the dimeric stability. (C) 2021 Elsevier B.V. All rights reserved.
NSTL
Elsevier
