Association of ionic liquids with cationic dyes in aqueous solution: A thermodynamic study

In this paper, the interactions between cationic dyes and the ionic liquids (ILs) have been studied by 31 P nuclear magnetic resonance (NMR), UV–Vis spectroscopy and conductometric measurements at different temperatures. It was shown that a decrease in the measured specific conductance of the (dye   +   IL) mixtures was caused by the formation of non-conducting or less conducting (dye   +   IL) associates. The associates were formed by 1:1 ratio of cation of the cationic dyes and anion of the ILs by using the 31 P NMR and UV–Vis spectroscopy methods. The association constants were calculated by theoretical model based on the deviation from linear behavior, and the association constants were as high as 10 6 (L   ·   mol −1 ) 2 . Thermodynamic results imply that the formation process of association was exothermic nature. It is expected that the associates reported here would have promising application as active materials for the preparation of ion-selective electrode used in the determination of ILs concentrations.