Terbium organic framework with dual sensing pathways for 2,4-dinitrotoluene detection

Accurate determination of 2,4-dinitrotoluene (DNT) is vital for environmental protection and public health. Although fluorescent methods for DNT detection offer the advantages of simplicity, rapid response, and low cost, they often suffer from limited sensitivity and selectivity due to sole reliance on the inner filter effect. In this work, a novel terbium organic framework (denoted as Tb-BCA) was synthesized using a carefully designed ligand, 2',5'-biphenyl-[1,1':4',1''-terphenyl]-4,4''-carboxylic acid (BCA). Tb-BCA exhibited strong green emission at 545 nm arising from the ⁵D₄→⁷F₅ transition of Tb³⁺, efficiently sensitized by the BCA ligand. The π-π stacking between DNT and the BCA ligand, together with the coordination of DNT to the central Tb³⁺, enhanced the sensing performance by improving molecular capture efficiency and inducing electron density perturbation, thereby intensifying the inner filter effect quenching response. The extended π-system further provides a hydrophobic microenvironment that preferentially enriches hydrophobic nitroaromatic compounds, contributing to improved selective recognition, with an enrichment factor of up to 207. Benefiting from these characteristics, the fluorescence intensity of Tb-BCA was quenched by up to 86.4% at 10 μM DNT. The response exhibited a linear relationship with the logarithm of DNT concentration over the range of 0.1-20 μM (R² = 0.99), with a limit of detection of 11.2 nM. The proposed method was successfully applied to wastewater monitoring by fabricating a thin-film sensing probe, yielding satisfactory results. This study provides a new strategy for enhancing the sensing performance of fluorescent probes through molecular-level regulation of the coordination environment.