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Phthalide-type dyes in aqueous variable alcohol solution were studied by UV-vis absorption spectroscopy. In this study, 7-[4-(diethylamino)-2-ethoxyphenyl]-7-(1-ethyl-2-methyl-1H-indol-3-yl)furo[3,4-b]pyridin-5 (7H)-one ("Blue-63") was used. Generally, a blue shift is observed from dyes in higher-carbon-number-alcohol solvents. The results indicated the dye equilibrium constant in aqueous alcohol solutions. The equilibrium constant (K), Gibbs energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) of the dye, depending on temperature change, were also calculated using UV absorbance.