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 (H3L), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd2+ and Zn2+ ions selectively in the off-on mode based on the AIE of their complexes in the media of THF/HEPES and THF/H2O, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn2+ and Cd2+ were 9.85 x 10(-9) M and 1.27 x 10(-7) M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn2+ (1) and Cd2+ (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 Cd2+ and Zn2+ ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd2+ ions were successfully differentiated from Zn2+ ions. Moreover, the detection of Cd2+ and Zn2+ ions was realized qualitatively via test paper and quantitatively in water.

Automated summary

A multi-binding site chemosensor with excited-state intramolecular proton transfer behavior was prepared and shown to selectively detect Cd2+ and Zn2+ ions based on the AIE characteristics of their complexes. Detection limits for Zn2+ and Cd2+ were determined and the formation of aggregates in the detection system was confirmed. Different coordination modes with the chemosensor resulted in emission at different wavelengths, allowing for successful differentiation between Cd2+ and Zn2+ ions.