A multi-binding site hydrazone-based chemosensor for Zn(ii) and Cd(ii): a new strategy for the detection of metal ions in aqueous media based on aggregation-induced emission.

A multi-binding site chemosensor, N-(3-methoxy-2-hydroxybenzylidene)-3-hydroxy-2-naphthahydrazone (HL), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd and Zn ions selectively in the "off-on" mode based on the AIE of their complexes in the media of THF/HEPES and THF/HO, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn and Cd were 9.85 × 10 M and 1.27 × 10 M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn (1) and Cd (2) complexes were prepared to investigate the response mechanism. Powder X-ray diffraction and single crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. The chemosensor coordinates with the Cd and Zn ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd ions were successfully differentiated from Zn ions. Moreover, the detection of Cd and Zn ions was realized qualitatively via test paper and quantitatively in water.