Influence of temperature and ethanol content on aggregation of rhodamine 6G molecules in aqueous ethanol solutions

Abstract

535.343.32 The effect of temperature on absorption spectra of Rhodamine 6G at concentrations of 10 -6 and 10 -3 M in water:ethanol solutions of various ethanol content was studied. The dimeric molecular fraction of Rhodamine 6G (10 -3 M) was found as a function of temperature and ethanol content in the aqueous solution. It was shown that the absorption spectrum of Rhodamine 6G dimers (10 -3 M) is dependent on temperature and ethanol content in the aqueous solution. Based on the relationship between J-and H-bands in the absorption spectrum of Rhodamine 6G dimers, both the angle between planes of associated Rhodamine 6G dye molecules and the free enthalpy of association were calculated. The structure of Rhodamine 6G dimers depends essentially on the ethanol content and aqueous ethanol solution temperature while experiencing the most temperature changes at an ethanol concentration of 25%.Introduction. The solvent effect on the efficiency of physicochemical processes occurring in solutions of various compounds has great scientific and practical significance. However, the behavior of molecular systems in solution have not yet been described by unified concepts despite the importance of the problem and the attention paid to it. Many questions (the nature of the interaction between molecules of the liquid and the dissolved compound, the mechanism of energy exchange between them, the reasons for the solvent effect on the reactivity, etc.) remain unanswered. This applies fully to widely used solvents such as water, alcohols, and their mixtures. The nature and character of intermolecular interactions, including molecular aggregation in solutions of complicated organic compounds, have recently been studied for the potential of controlling radiative and radiationless relaxation of excited states by varying the structure of the dissolved organic molecules and their closest environment. Furthermore, the study of the photonics of dye molecules led to conclusions about the structure of aqueous alcohol solvents with various contents of alcohol in them that could act as a heterogeneous system [1,2]. The physicochemical properties of such mixtures depend nonlinearly on the quantitative ratio of binary solvents.The goal of our work was to study spectroscopically the effect of the composition of aqueous alcohol mixtures on the association of Rhodamine 6G molecules and their optical characteristics. Solutions of this dye were studied at various temperatures in order to enhance the observed optical effects.Experimental. Association of Rhodamine 6G molecules at concentrations of 1⋅10 -3 and 1⋅10 -6 M in aqueous ethanol solutions was studied using absorption spectra. Solutions with varying water and ethanol content were prepared by taking a certain volume of Rhodamine 6G stock solution with a concentration of 5⋅10 -3 M in water and adding the required amounts of ethanol and water. The alcohol content in the solution was expressed in volume percent of anhydrous alcohol in solution.Electronic absorption spectra were measured on a Speko...

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