Stable Interpenetrated Zirconium-Based Metal-Organic Framework for the Fluorescence Detection of MnO₄

In this work, a novel stable zirconium-based metal-organic framework (Zr-MOF) with the formula [Zr₆O₄(OH)₄(PVDC)₆]₄·66DMF (Zr-1, H₂PVDC = (E,E)-2,5-dimethoxy-1,4-bis[2-(4-carboxylatestyryl)]benzene; DMF = N,N-dimethylformamide) was synthesized by introducing a linear phenylenevinylene-based carboxylate ligand to react with ZrCl₄ under solvothermal conditions. According to single-crystal X-ray diffraction measurement, complex Zr-1 featured a 2-fold interpenetrated framework, in which the single coordination framework possessed a structure similar to that of the well-known Zr-MOF, UiO-66, constructed from [Zr₆O₄(OH)₄]¹²⁺ clusters and carboxylate ligands PVDC^2-. Due to the introduction of the phenylenevinylene-functionalized ligand, complex Zr-1 exhibited a unique fluorescence sensing performance toward permanganate (MnO₄^-) with different concentrations. At low concentrations, the fluorescence emission intensity of Zr-1 around 510 nm was enhanced significantly with an increase in the concentration of MnO₄^- in an aqueous suspension. However, while excess MnO₄^- was added into the suspension, the fluorescence emission intensity decreased significantly, and the single emission peak turned into five emission peaks upon the addition of MnO₄^-. Such a phenomenon has been scarcely reported in previous MOF-based fluorescence sensors. Moreover, complex Zr-1 showed high anti-interference capability for the detection of MnO₄^- both at low and high concentrations. This work may pave a new way for the development of MOF-based fluorescence sensing platforms.