The sensing and anti-counterfeiting performance of novel tripodal cauldron-like lanthanide compounds: from molecule...

Rapid, sensitive, and selective detection of explosives and pesticides is vital for environmental and human health. Herein, three tripodal cauldron-like compounds, [NH₂(CH₃)₂]₆[Ln₃L₃(OAc)₃]·4H₂O·DMA·3CH₃CN (L-Ln, Ln = Tb, Eu and Gd; DMA = N,N-dimethylacetamide), have been synthesized and characterized based on H₄L, where a flexible diethylene oxide group is terminated by two 2,6-pyridinedicarboxylic acid (DPA) moieties. In these complexes, Ln^III contained macrocycle is protected by folded alkyl ether chains of H₄L. Benefiting from its bright green emission and excellent water stability, L-Tb enables rapid and sensitive detection of 4-nitrotoluene (4-NT) and paraquat (PQ) in aqueous media. For portability, a luminescent film (L-Tb@PMMA) was prepared to render stronger luminescence, mechanical robustness, and enhanced sensing capability. To further expand its practical applications, L-Tb@SA was developed using sodium alginate (SA) as the matrix. Leveraging its excellent hydrophilicity, L-Tb@SA exhibited enhanced sensing performance, characterized by an exceptionally fast response time (<20 s) and low detection limits (LOD) for 4-NT of 50 nM and PQ of 24 nM, respectively. L-Tb@SA film also enabled efficient detection and high recovery of 4-NT in Yellow River water and PQ in soil samples. The sensing mechanisms were elucidated through a combination of experimental and theoretical approaches. Moreover, L-Ln based security inks (Ln = Eu, Tb) exhibited reversible 'on-off' luminescence switching in response to 'NH₃-HCl' vapors, underscoring their potential for information encryption and anti-counterfeiting applications. These results demonstrate the strong potential of lanthanide-based materials for practical use in environmental monitoring and anti-counterfeiting.