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KMID : 0385520090220020159
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Analytical Science & Technology
2009 Volume.22 No. 2 p.159 ~ p.165
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A thermodynamic analysis on thermochromism of fluoran dyes
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Kim Jae-Uk
Ji Myoung-Jin
Kim Jong-Gyu
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Abstract
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The thermochromism of fluoran has been examined. The DCF exists as a colorless lactone in aprotic solvents. However, the DCF exists in the form of an equilibrium mixture of a colored zwitter-ion and a colorless lactone in protic solvents. When an acid is added to the solution, the DCF exists an equilibrium mixture as a colorless lactone and a colored cation even in aprotic solvents. In order to understand the interaction between the DCF and the solvent, absorption spectra of the DCF in various solvents were measured. The thermodynamic parameters of the DCF have also been investigated. From the variation of absorbance with temperature, the standard enthalpy changes ΔH? of the equilibrium between the lactone and the zwitter-ion in various solvents have been determined. The standard enthalpy change ΔH? is approximately -2.0 kJ/㏖ in protic solvents. In acidic solution, the standard enthalpy change is measured to be to zero in protic solvents within the experimental error. When the carboxylic group is protonated in acidic solution, a poor interaction between the dye and the solvent is expected.
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KEYWORD
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thermochromism, functional dye, equilibrium constant, enthalpy
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