Two copper(II) complexes, 1 and 2, of two tridentate N-donor ligands, L₁1 and L₂2 [L₁1 = dansyl derivative of bis-[3-(dimethylamino)-propyl]amine; L₂2 = dansyl derivative of dipropylenetriamine] were synthesized and characterized. The quenched fluorescence intensity of complexes 1 and 2, in degassed methanol or aqueous (buffered at pH 7.2) solution, was found to reappear on exposure to nitric oxide. This is attributed to the reduction of paramagnetic Cu(II) center by nitric oxide to diamagnetic Cu(I).