Fluorescent Nitric Oxide Detection by Copper Complexes Bearing Anthracenyl and Dansyl Fluorophore Ligands

Anthrancenyl and dansyl fluorophore ligands [AnCH2pipCS2K (1), Ds-Hen (2), Ds-HAMP (3), Ds-HAQ (4), and
Ds-HAPP (5)] were prepared for coordination to CuII. Five Cu complexes, [Cu(AnCH2pipCS2)2] (6), [Cu(Ds-en)2]
(7), [Cu(Ds-AMP)2] (8), [Cu(Ds-AQ)2] (9), and [Cu(Ds-APP)(OTf)] (10), were synthesized as candidates for detecting
nitric oxide (NO) by fluorescence and characterized by X-ray crystallography. A decrease in fluorescence compared
to that of the free ligands (1−5) was measured following the formation of the corresponding five CuII complexes
6−10. Fluorescence was restored in the presence of NO in CH3OH/CH2Cl2 solutions of the compounds. Complexes
7, 8, and 10 exhibited a fluorescence response to NO in pH 7.0 or 9.0 buffered aqueous solutions. Spectroscopic
studies revealed that NO-induced fluorescence enhancement in these CuII complexes occurs by reduction to CuI.
The present studies demonstrate that CuII complexes are effective as fluorescent probes for detecting NO in both
organic and aqueous environments.