Synthesis, Structure And Fluorescence Properties Of Rare Earth Complexes Based On Bipyridinecarboxylic Acid

Rare earth ions with unique 4f energy level make its fluorescence emission with bright color,high purity,wide band range,large Stokes shift and a series of other attractive features.Rare earth luminescent materials have long been recognized having broad prospects in the field of luminescent materials.However,because of transition forbidden of f-f energy level transition,the molar extinction coefficient of f-f transition is very low.Nowadays,one of the most productive method to overcome this obstacle is utilizing organic ligands as "antenna" to help rare earth ions absorb energy and realize intense rare earth ions fluorescence emission.In this study,we mainly utilize two kinds of dipyridine carboxylic acid ligands coordinating with Eu(III)and Tb(III)ions to obtain two kinds of rare earth complexes and achieve efficient fluorescent emission.This thesis can be divided into three parts:(1)Iintroduction.The background,luminescent mechanism,and current study of luminescent rare earth complexes are introduced in this part.(2)The second chapter.A kind of new lanthanide complexes[Ln2(bpydc)3·3H2O]·H2O 3CH3OH(1,Ln = Eu,Tb,Yb,Gd;Hbpydc= 2,2’-bipyridine-6,6’-dicarboxylic acid)were synthesized with a 2,2’-bipyridine-6,6’-dicarboxylic acid(Hbpydc)ligand,and then characterized by single crystal X-ray diffraction,Fourier transform infrared spectroscopy,ultraviolet absorption spectra,fluorescence spectra and phosphorescence spectra.Results of single crystal X-ray diffraction show that the structure of the complex is based on two metal centers which are coordinated with three ligands in total and it belongs to monoclinic system with space group P21/c,a= 1.36128(17)nm,b= 1.8806(3)nm,c= 1.5855(2)nm,α=90°,β= 92.619(3)°,)γ= 90°,V= 4.0547(9)nm3,Z= 2.Spectral analysis indicates that the complexes of Eu(III)and Tb(III)respectively show intense character emission peaks at 612 nm and 548 nm in the fluorescence spectra;the calculated triplet energy level of ligand(26666cm-1)is favorable for energy transfer into those of Eu(III)(5D0,17300 cm-1)and Tb(III)(5D4,20500 cm-1);there is obvious "antenna effect" and efficient energy transfer between the ligand Hbpydc and lanthanide acceptors.(3)The third chapter.A kind of new complex[Ln2(bpydc)3·2DMF]n(2,Ln= Eu,Tb,Gd;Hbpydc= 2,2’-bipyridine-5,5’-dicarboxylic acid)was synthesized with a 2,2’-bipyridine-5,5’-dicarboxylic acid(Hbpydc)ligand,and then characterized by single crystal X-ray diffraction,Fourier transform infrared spectroscopy,fluorescence spectra and phosphorescence spectra.Results of single crystal X-ray diffraction show that the complex 2 Tb belongs to triclinic system with space group P-1,a= 1.39657(2)nm,b= 1.40874(1)nm,c= 1.45241(1)nm,a= 90.887(1)°,β= 115.261(1)°,γ=113.951(1)°,V= 2.29931(5)nm3,Z= 2.Spectral analysis indicates that the Eu(III)and Tb(III)complexes respectively show intense emission peaks at 612 nm and 542 nm in fluorescence spectra;the calculated triplet energy level of ligand(26178 cm-1)is favorable for energy transfer into those of Eu(III)and Tb(III);there is efficient energy transfer between the ligand and lanthanide acceptors.Besides,when we analyze the energy transfer efficiency of l Ln and 2 ·Ln(Ln= Eu and Tb),we fond that the former’s energy transfer efficiency is a little bit greater than the latter’s but their triplet state energys have little differences.Thus,we consider that their structural differences contribute to the differences in their energy transfer efficiency.