Copper(II) complexes as turn on fluorescent sensors for nitric oxide

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).