A naphthyridine based macrocyclic “switching on” fluorescent receptor for cadmium

A new macrocyclic receptor 1 having [1,8]-naphthyridine fluorophore is designed and synthesized for selective fluorescence sensing of Cd2+. Receptor 1 selectively responds to Cd2+ over other tested metal ions via a large enhancement of emission intensity due to the cation-induced CHEF (chelation enhanced fluorescence) effect. Receptor 1 although exhibits some affinity towards Zn2+, it selectively binds Cd2+ over Zn2+. Binding and selectivity were examined by 1H-NMR, fluorescence, UV–vis, mass and IR-spectroscopic techniques.