Tetraphenylethylene-Imidazole-Based MOFs for Broad Spectrum and Chain-Length Complementary Detection of Polyfluoroalkyl Substances

This work addresses the challenge of detecting per- and polyfluoroalkyl substances (PFASs) in water by developing fluorescent metal-organic frameworks (MOFs), designated as <b>MOF1</b>, <b>MOF2</b>, and <b>MOF3</b>. These MOFs were constructed by using the d¹⁰ metal of Zn(II) and Cd(II) as nodes, 1,1,2,2-tetrakis(4-(1-imidazolyl)phenyl)ethylene (Tipe) as the primary ligand, and varied aromatic multicarboxylate coligands. <b>MOF1</b> exhibits broad spectrum recognition capability, demonstrating fluorescence quenching toward both long- and short-chain PFASs. In contrast, <b>MOF2</b> and <b>MOF3</b> display selective responses: <b>MOF2</b> shows fluorescence enhancement for long-chain PFASs, whereas <b>MOF3</b> exhibits fluorescence quenching for short-chain PFASs, thereby establishing a complementary detection system. All three MOFs possess superior sensing performance, including a low detection limit down to 0.22 ppm (corresponding to 0.43 μM), strong anti-interference ability, and good cycling stability. Mechanistic investigations reveal that fluorescence quenching results from electron transfer induced by the electron-withdrawing groups of PFASs, while the fluorescence enhancement observed in <b>MOF2</b> arises from the restricted intramolecular motion of organic ligands due to the adsorption of PFAS molecules within the framework pores.