A Stable Zn II Metal–Organic Framework with a Benzothiadiazole Carboxylate Ligand as Fluorescent Sensor for Zr 4 + , H 2 PO 4 – , and VB1 in Living Cells

A new N/O polydentate ligand with benzothiadiazole units (4-(7-(1H-pyrazol-4-yl)benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid, H₂PZBTB) has been used to synthesize a stable zinc(II) metal-organic framework (MOF) under solvothermal conditions with the formula {[Zn₂(PZBTB)₂(H₂O)₂]·0.5DMF}_n (JXUST-60, where JXUST denotes Jiangxi University of Science and Technology; DMF = dimethylformamide). JXUST-60 possesses a two-dimensional (2D) planar architecture, while interlayer interactions via π-π stacking result in the formation of a three-dimensional (3D) packing structure. JXUST-60 maintains structural integrity after being immersed in water and aqueous solutions with pH = 3-13 for 24 h. Fluorescence sensing experiments demonstrate that JXUST-60 can function as a turn-on MOF sensor for Zr⁴⁺, dihydrogen phosphate (H₂PO₄^-), and vitamin B1 (VB1) through naked-eye recognition, with low detection limits of 0.06, 0.13, and 0.09 μM, respectively. It is worth noting that JXUST-60 is a rare sensor that recognizes VB1 through the turn-on effect and is the only Zn^II MOF fluorescence sensor capable of recognizing Zr⁴⁺ to date. In addition, the cyclic test demonstrates that JXUST-60 is a reusable sensor material. More importantly, JXUST-60 has good biocompatibility and low cytotoxicity to sense VB1 in living cells.