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 MOF1, MOF2, and MOF3. 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. MOF1 exhibits broad spectrum recognition capability, demonstrating fluorescence quenching toward both long- and short-chain PFASs. In contrast, MOF2 and MOF3 display selective responses: MOF2 shows fluorescence enhancement for long-chain PFASs, whereas MOF3 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 MOF2 arises from the restricted intramolecular motion of organic ligands due to the adsorption of PFAS molecules within the framework pores.