ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 54, Number 5
JKCSEZ 54(5)
October 20, 2010 

Two different dyes containing the same molecular weight but different chemical structure have been utilized for the study of thermodynamic parameters. In this study, {3-(4-(diethylamino)phenyl)-3-(1-ethyl-2-methyl-1H-indol-3-yl)isobenzofuran- 1(3H)-one} (Blue 502) and {3-(4-(diethylamino)-2-methylphenyl)-3-(1,2-dimethyl- 1H-indol-3-yl)isobenzofuran-1(3H)-one} (Blue 402) were used. It has been performed by measuring UV spectra of the two dyes. In general, the blue shift has been observed from both dyes in higher carbon number alcohol solvents. Interestingly, Blue 502 showed higher stability than Blue 402 in the same conditions used in this study. And, the equilibrium constants (0.9 ~ 1.0) of the dyes depending upon temperature change were also calculated using UV absorbance. The standard enthalpy calculated from equilibrium constants and molar absorptivity(ε) are 10.94 kJ/mol in Blue 402 and 9.010 kJ/mol in Blue 502, respectively.