Syntheses, Structures, and Ratiometric Fluorescent Sensing Properties of a Series of Lanthanide Coordination Polymers
Bin Tan, Ting-Hui Zhuang, Ever Velasco, Kai Xing, Zhao‐Feng Wu, Xiao‐Ying Huang
Abstract
The plentiful structural features and excellent fluorescence properties of lanthanide coordination polymers (Ln-CPs) have garnered much attention in recent years. Herein, 1,4-naphthalic acid (1,4-NDCH2) has been used to assemble a series of Eu-CPs formulated as [Eu2(1,4-NDC)3(DMF)(H2O)] (1-Eu), [Eu2(1,4-NDC)3(DMF)] (2-Eu), and [Eu2(1,4-NDC)3(DMF)4]·DMF (3-Eu). Single-crystal structure analyses reveal that 1-Eu and 2-Eu feature three-dimensional (3D) structures with a 3-nodal net and an oab topology, respectively, while 3-Eu exhibits a 2D network. FL measurements indicate that 2-Eu exhibits dual-emitting FL of emission generated from 1,4-NDC2– and the characteristic red emission of Eu3+, while 1-Eu and 3-Eu exhibit only characteristic emission from Eu3+ ions. The dual-emitting character of 2-Eu is not only dominated by inefficient intermolecular energy transfer from 1,4-NDC2– to Eu3+ ions but also related to its structure features. The FL properties of 1-La, 1-Y, and 2-Lu are comparatively studied to better understand the dual-emission mechanism of 2-Eu. Moreover, the dual-emitting character could make 2-Eu a reliable ratiometric FL assay for low concentrations of Fe3+, CrO42–, and nitro-containing explosive molecules. The sensing process combined with a colorimetric change from red to light purple realizes a convenient visual recognition of the analytes. The benign FL sensing properties as well as the excellent chemical stability of 2-Eu under a wide range of pH and thermal conditions make it a good candidate as a chemical FL sensor even under harsh conditions. This work is expected to give certain guidance for designing dual-emitting FL Ln-CPs toward ratiometric FL sensing applications.