Study on fluorescence properties of rare earth complexes influenced by steric effect

The rare earth complexes Tb(o-BrBA)3, Tb(m-BrBA)3 and Tb(p-BrBA)3 were synthesized using o-, m-, p-bromo benzoic acids (2-bromo benzoic acid, 3-bromo benzoic acid and 4-bromo benzoic acid) as ligand, respectively. The UV spectra showed that the absorption ability of Tb(m-BrBA)3 was the strongest. However, the fluorescent intensity of Tb(o-BrBA)3 was the weakest. The effect of the molecular structure, the energy level of Tb3+ and energy transfer efficiency from ligands to Tb3+ were discussed to explain the experimental results. The results indicated that, due to the large atomic radius of bromine, the steric effect caused by the different substitution bromine on the benzene ring might strongly affect the bond length formed by the coordination atoms and Tb3+. The longer the bond length was, the lower the efficiency of energy transfer was, and the weaker the fluorescent intensity was.