A Thermodynamic Study on Phthalide-Type dyes in Aqueous Alcohol Solutions

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 (∆G), enthalpy change (∆H), and entropy change (∆S) of the dye, depending on temperature change, were also calculated using UV absorbance.