Effects of water molecules on luminescence in europium and terbium coordination polymers with p-fluorobenzoic acid as ligand

Our previous experimental observations show that the crystal structure of lanthanide luminescent complexes synthesized in aqueous solution usually contains a large number of coordination water molecules or free water molecules. In order to probe the influence of water molecules on luminescent processes of lanthanide complexes, the photoluminescence properties of Ln-FBA (Ln = Eu and Tb, FBA = p-fluorobenzoic acid) coordination polymers at different ambient temperatures, in different solvents and aqueous DMSO solutions with different volume concentrations were systematically investigated. The experiment results show that the presence of water molecules can promote the energy transfer from FBA ligand to Ln3+, but at the same time, can cause luminescent non-radiation quenching of lanthanide ions. In addition, the variation of emission intensity ratio of 615 nm/591 nm peaks of Eu3+ with increasing the volume concentration of H2O can be potentially used for the quantitatively detection of water traces in organic solvents. In order to suppress the non-radiation quenching caused by the water molecules, Ln-FBA (Ln = Eu and Tb) coordination polymers were embedded into the PVP matrix to prepare Ln-FBA@PVP hybrid materials. The photoluminescence investigation indicates that PVP can not only block the quenching effect of water molecules on luminescence, but also effectively sensitize Eu3+ and Tb3+ luminescence. These experimental conclusions are useful for probing the influence of water molecules on luminescent processes of lanthanide complexes, quantitatively detecting water traces in organic solvents and enhancing the photoluminescence intensity in lanthanide complexes.