Amide-functionalized lanthanide metal–organic frameworks: smart double ratiometric fluorescence sensing of thiodiglycolic acid and tunable luminescence

Abstract

Lanthanide metal–organic frameworks (Ln-MOFs) have excellent optical properties and structural diversities, providing a unique platform for the development of sensing and optical materials. Herein, two series of Ln-MOFs, [Ln(L)(DMF)(H₂O)]·DMF (Ln-DMF, DMF = N,N-dimethylformamide), and [Ln(L)(DMA)(H₂O)]·DMA (Ln-DMA, DMA = N,N-dimethylacetamide) (Ln = Eu, Gd, Tb, H₃L = C₆H₃(CONH)₃(C₆H₄)₃(COOH)₃), were fabricated using the same H₃L ligand under solvothermal conditions, giving 3D supramolecular and 2D layered structures, respectively. The good water and acid–base stabilities of Tb-DMF and Tb-DMA provide prerequisites for their fluorescence sensing applications. Tb-DMF and Tb-DMA were used as double ratiometric fluorescence sensors for detecting thiodiglycolic acid (TDGA) with low LODs, excellent anti-interference, and visualization. Moreover, these sensors were applied to the detection of TDGA in real urine samples with satisfactory recoveries (96.34–110.75%). Then, two portable smartphone-based platforms were used to monitor TDGA with high precision. Moreover, the practicability and availability of smartphones in the TDGA sensing process were further improved by establishing logic gates. By adjusting the molar ratios of Eu³⁺, Gd³⁺, and Tb³⁺ ions, nine bi-metallic doped Eu_xTb_1−x-DMA (x = 0.10–0.90) and one tri-metallic doped Gd_0.95Eu_0.03Tb_0.02-DMA near white-light MOFs with a quantum yield of 25.73% were obtained. This study provides a strategy for the construction of multifunctional materials with double ratiometric fluorescence sensing and tunable luminescence.