Prototropic behavior of norharmane within ionic liquids

•Prototropic forms of norharmane are investigated in nine different ionic liquids (ILs).•Role of cation and anion of ILs is explored in dictating the norharmane prototropism.•Acidity of the cation of the IL controls relative presence of the prototropic forms in an IL.•For similar acidity cation, Lewis basicity of the anion of the IL mainly decides probe prototropism.•ILs as designer solvents to control the prototropic forms of a solute is established.