Prototropic behavior of norharmane within ionic liquids

Abstract Ionic liquids are established as alternate solvents for several traditional organic solvents as well as aqueous-based media in many areas of chemistry. Proton transfer reactions exhibit a high dependency on the nature of the solubilizing media. In the present study, using a representative prototropic probe norharmane (β-carboline) and nine different ionic liquids, we have demonstrated that the relative presence of the various prototropic forms of the probe in an ionic liquid is controlled by a delicate balance of the acidity of the cation and the Lewis basicity of the anion of the ionic liquid. UV–vis molecular absorbance is used to obtain information on ground-state prototropism whereas steady-state and time-resolved fluorescence are used to investigate prototropic forms in the excited-state. Ionic liquids are demonstrated to act as designer solvents in regulating prototropic behavior.