Design,Synthesis And Luminescence Properties Of Lanthanide Complexes With O-Vanillin-Based Schiff Base Ligands

In this paper,three new Schiff base ligands H₂L¹,H₂L² and H₂L³ were synthesized from the Schiff base condensation reactions of symmetrical organic diamines containing benzene rings and o-vanillin.H₂L^1-3 have polyphenylene rings and abundant coordination sites.They can show a variety of coordination modes with rare earth?Ln?and d transition metals such as Zn,Cd,Ni,etc.Meanwhile,secondary ligands such as 3-methoxycatechol and dibenzoylmethane have been added to the reaction system to construct multinuclear and high nuclear rare earth complexes.The secondary ligands can transfer absorbed light energy to lanthanide centers,resulting in the enhancement of luminescence properties of the complexes.Here,four series of d-4f complexes were synthesized,including 4-nuclear Ni-Ln?Ln=Eu,Yb?,4-nuclear Zn-Ln?Ln=Eu,Yb,Er,Nd?,4-nuclear Zn-Nd and 12-nuclear Zn-Ln?Ln=Eu,Sm,Nd?.H₂L^1-3 were characterized using various techniques,including nuclear magnetic resonance.All lanthanide complexes were characterized by ultraviolet,XRD powder diffraction,thermal analysis,SEM,elemental analysis and fluorescence measurement.The study of their luminescence properties shows that,the chromophoric ligand centers such as Zn/L can efficiently transfer the absorbed energy to the lanthanide ions,resulting in the lanthanide luminescence.In this paper,the fluorescence sensing experiments of nitrobenzene explosives and metal ions were carried out on 12-nuclear Zn-Sm and Zn-Eu complexes,respectively.Interestingly,the nitrobenzene explosive 1,4-dinitrobenzene?1,4-DNB?exhibits a specific fluorescence quenching effect towards the 12-nuclear Zn-Sm complex,while the metal ion Ag⁺can efficiently enhance the fluorescence intensity of the 12-nuclear Zn-Eu complex.