A helical salicylaldehyde Schiff base exhibiting aggregation-induced emission and selective recognition of Cu2+ ions

A racemic salicylaldehyde Schiff base (L) containing a pyridine-2,6-dicarboxamide scaffold was successfully synthesized and characterized. L exhibited a typical aggregation-induced emission (AIE) characteristic in the mixed solvent of THF/H₂O. The UV–Vis absorption spectra and fluorescence emission spectra showed a high selectivity and sensitivity of L for the recognition of Cu²⁺ over other ions in the solution of THF/H₂O (2:3), and indicated L can be used as a turn-off fluorescent probe for Cu²⁺. The stoichiometric ratio, association constant, and the detection limit of probe L toward Cu²⁺ were estimated using Job's plot method, UV–Vis spectra titration, and fluorescence spectra titration. More importantly, a Cu(II) complex was synthesized from the coordination interaction of probe L with Cu²⁺ and characterized by X-ray crystal diffraction technique. The crystal structure well illustrated the binding mode of L with Cu²⁺, contributing to the further understanding of the coordination mechanism.