Luminescent properties of multi-stimuli-responsive Ln-BPDC-Phen Lanthanide complexes

Abstract

Stimuli-responsive smart luminescent materials have attracted more and more attention recently. A series of lanthanide organic complexes, [Ln2(BPDC)3(Phen)2(DMF)2]·5H2O (Ln: lanthanide = Eu, Tb, EuxTb1−x, H2BPDC = 2,2′-Bipyridine-5,5′-dicarboxylic acid, H2Phen = 1,10-phenanthroline, DMF = N,N-dimethylformamide), were synthesized and characterized to be iso-structural. The complexes demonstrate selective and significant response to Fe3+ ions, leading to fast and accurate measuring of Fe3+ ions. Interestingly, the complexes exhibit diverse luminescent response to two isomers 2, 6-pyridine dicarboxylic acid (DPA) and 3, 5-pyridine dicarboxylic acid (H2PDC). The green emission due to Tb3+ ions is enhanced by DPA upon excitation of 280 nm, which is ascribed to the absorption of DPA. Whilst it is quenched by DPA with the excitation of the ligands (339 nm). However, H2PDC quenches both the green and red emissions regardless of the excitation wavelength. The reason is that DPA provides more possibilities of the ligand exchange with the complex due to the suitable position of the carboxylic acid functional groups on the pyridine ring than H2PDC. Simultaneously, the luminescent response of the complex to DPA enables emission color tunability, which allows the complex to recognize and measure DPA/H2PDC isomers visually and easily. Moreover, the complex exhibits a wide-range (110–360 K) temperature sensing with high Sr = 3.92 %K−1 at 180 K. The multi-stimuli-response of the complexes makes them potential applicants for multi-functional sensing materials.