A Luminescent Metal-Organic Framework with Boosted Picric Acid Fluorescence Detection Performance via a Complementary Capture-Quench Mechanism

The strong explosiveness, toxicity and environmental pollution of picric acid make its sensitive detection important. Recently, LMOF materials are showing great potential toward efficient detection of PA. However, hindered by the weak connections between LMOFs and analytes, a feasible fluorescence selectivity and sensitivity to desired compounds by constructed LMOFs remain challenging. Herein, we propose a new strategy by using the innate adsorption ability of MOFs. We choose NDC−Zn, a highly stable LMOF with unique pore structures. The topology of ligands can capture PAs specifically inside the pores and the selectivities are further elevated. PET effects are boosted due to longer and closer contact between ligands and trapped PAs, thus higher sensitivity is also achieved. Besides, a fluorescence enhancement at a visible wavelength was found as the concentration of PA increased, suggesting a potential application of naked-eye recognition for PA. NDC−Zn exhibited an outstanding detection sensitivity for PA with a quenching constant of 49657 M⁻¹, as well as distinctive fluorescence quenching among 9 nitro explosives. From DFT calculations, the fluorescence quenching mechanisms such as PET and the complexation between H₂NDC and PA were supported.