Synthesis, Characterization And Fluorescence Properties Of Rare Earth Complexes With β-diketone Ligand

The lanthanide complexes withβ-diketone ligands have high ability of UV-vis excitationfluorescence, and the ligands make rare earth ions emit strong characteristic fluorescence byorganic ligands'strong UV-vis absorbance and efficient energy-transfer between the ligandsand lanthanide ions. Therefore,designing and synthesizing novelβ-diketone kind ofcompounds is of great importance for searching and developing novel sensitizers for rareearth ions and designing the structures of ligands is also a key point to discover newfluorescent sensitizers of rare-earth ions.Two novelβ-diketone ligands named 1,5-bi(3,4,5-trihydroxy) benzoylacetylacetone(L₁)and 1-(3,4,5-trisbenzyloxy)benzoyl-5-benzoyl acetylacetone (L₂) were synthesized startingfrom 3,4,5-trihydroxybenzoate as the raw material through Claisen reaction. The structures ofboth ligands were charaeterized by the Fourier transform infrared (FT-IR) spectrum,elemental analysis(EA),thermal analysis and proton nuclear magnetic resonance (1H-NMR)in detail.One dinuclear complex Tb2(L₁)₃·4H₂O , two ternary complexes Ln(L₂)3phen and twobinary complexes Ln(L₂)₃·2H₂O were synthesized by the reaction of rare earth chloride (Eu,Tb) with ligand L₁ and L₂, respectively. The structures of all complexes were charaeterized byFT-IR, EA. The thermal analysis of complexes was examined by TG-DSC. The content ofEu(III) and Tb(III) were determined by EDTA titration with xylenol orange as an indicator.All results show that the structure of the five complexes is entirely consistent with expectedcomplexes and the complexes have higher thermostabilityMeanwhile, the fluorescence properties of complexes were measured. The results showthat the effective energy transfer process occurred form the ligands L₁ and L₂ to lanthanideions, and subsequently the central ions can be sensitized effectively. The ligand which haslarger conjugate system is a better fluorescence sensitizer than the smaller conjugate system ligands. In particular,the ternary complex and binary complex of ligand L₂ have a muchhigher fluorescence intensity than the complex of ligand L₁. The Tb(â…¢) complex exhibit amore excellent luminescence property than the Eu(â…¢) complex for the same ligand. Morever,comparing to the binary complexes,the introduction of secondary ligand phen significantlyenhanced the luminescent intensity of ternary complex. Through testing and calculation, theresults show that Tb (â…¢) complex has higher quantum efficiency than Eu (â…¢) complex.The fluorescence emission of complexes is extremely narrow half-band width and goodmonochromaticity, which is significant for the developing of rare earth complexes efficientluminescent materials.