A colorimetric probe for copper(II) ion based on 4-amino-1,8-naphthalimide

A novel fluorescent probe with naphthalimide as fluorophore and di(2-picolyl)amino unit as receptor for Cu(II) was designed and synthesized. In water/acetonitrile solution, the presence of Cu2+ ions induced significant blue shift on the maximum absorption band as well as complete fluorescence quenching due to the formation of a 1:1 metal–ligand complex. It exhibited high selectivity toward Cu(II) and no interference from other metal ions was observed. The structure of the complex was characterized by single crystal X-ray diffraction experiments. The results of this research demonstrate successfully that excellent sensing properties can be achieved by a small organic compound with very simple structure. This is also the first single crystal structure which reveals directly the coordination pattern of fluorescent probe bearing di-2-picoly-amine unit with Cu(II).