Spectroscopic studies on the proton transfer reactions of 4-hydroxy-2-oxo-1,2-dihydroquinolin-3-carbonitrile with different amines in acetonitrile

► Proton transfer complexes of HQC with different amines were investigated. ► The formation constants were estimated and evaluated. ► A spectral method was suggested for HQC determination. ► The solid complexes were synthesized and characterized.