Luminescent lanthanide complexes based on 4,5-di(3,5-dicarboxylphenoxy)phthalic acid as enhanced fluorescence probes for highly selective detection of lead(ii) ions in water

Abstract

Six novel lanthanide complexes ([Nd₂(L)(H₂O)₆]_n·4.58n(H₂O) (1), [Ln(H₃L)(H₂O)]_n·0.5n(H₂O), Ln = Sm (2), Eu (3), Gd (4), Tb (5), Eu_0.18Gd_0.62Tb_0.20 (6)) have been hydrothermally synthesized based on the ligand 4,5-di(3,5-dicarboxylphenoxy)phthalic acid (H₆L). Single crystal X-ray diffraction reveals that complexes 1–6 are 2D structures, where 2–6 are isomorphic. Complexes 3 and 5 exhibit the characteristic fluorescence of Eu(III) and Tb(III) ions respectively, while complex 4 shows blue-green light emission based on the ligand. In particular, the ternary Eu/Gd/Tb complex 6 shows white light emission with a CIE (Commission International del'Eclairage) chromaticity coordinate of (0.330, 0.339) and hence close to pure white light emission. Moreover, complexes 3 and 5 display specific fluorescence-enhanced detection performance for Pb²⁺ ions: The interaction between Pb²⁺ ions and the ligand enhances the charge transfer efficiency between the ligand and the Eu(III) and Tb(III) ions and thus leads to fluorescence enhancement of complexes 3 and 5. More importantly, complex 3 exhibits the lowest detection limit of 4.72 nM for Pb²⁺ ions among the existing complex fluorescent probes. In addition, both complexes 3 and 5 show good performance for recycling and for the detection of Pb²⁺ in real water samples.