Coordination Assembly And Fluorescence Properties Of Pyridylhydrazone/amide-type Schiff Base

Two types of acylhydrazone Schiff base ligands（H₂L₁,H₄L₂）based on2,2’-dipyridine and one pyridinamide Schiff base ligand（H₄L₃）were synthesized,and a series of metal complexes were obtained.The experimental results indicate that the configuration of pyridylacylhydrazone ligand and the types of metal ions have significant effects on the structure of the complexes.The recognition characteristics of H₄L₂for a series of metal ions were investigated by UV-vis and fluorescence spectra.The results show that H₄L₂has selective recognition for Cu²⁺and could be used as a fluorescence sensor for Cu²⁺.The two different coordination modes of pyridinamide ligand H₄L₃and Cu²⁺reveal that the molar ratio of organic ligand to metal ion has a notable impact on the structure.Two helical Schiff base fluorescent probes（H₄L₄,H₄L₅）based on salicylaldehyde structural unit were synthesized.The fluorescence spectrum analysis results demonstrate that both probes exhibit specific recognition of Cu²⁺in aqueous medium.The specific binding mode of H₄L₄and Cu²⁺was further confirmed by cultivating single crystals of H₄L₄and Cu²⁺.In addition,the recognition ability of H₄L₅to F^-was investigated in THF,and the results verify that the sensing mechanism of H₄L₅to F^-was deprotonation,and the relevant detection limit was lower than 1.33×10^-7mol·L^-1.In addition,the ligand H₄L₅was used for simple detection of Cu²⁺and F^-.One Schiff base macrocyclic probe（H₈L₆）based on tetrastyrene was synthesized and its crystal structure was determined by X-single crystal diffraction.Macrocyclic H₈L₆exhibits distinct"ESIPT+AIE"properties and performs significant selective recognition of Al³⁺in THF/water mixed solutions,which are due to the restriction of ESIPT and imine group（-C=N-）isomerization and chelation enhanced fluorescence（CHEF）based on the coordination between H₈L₆and Al³⁺.