Tetraphenylethylene-based covalent organic frameworks as fluorescent chemosensor for rapid sensitive recognition and selective “turn-on” fluorescence detection of trace-level Al³⁺ ion

Tetraphenylethylene-based covalent organic framework (COF-DHTA) was prepared and then well characterized. COF-DHTA processes regular pore structure and high thermal stability. COF-DHTA suspension in DMF displays moderate fluorescence emission in DMF suspension and a highly selective fluorescence “turn-on” response towards Al³⁺ ions. The fluorescence intensity of COF-DHTA suspension at the emission peak 352 nm exhibits a good linear relationship with the concentration of the added Al³⁺ ions with a very low detection limit of 0.927 μmol/L. The selective and sensitive fluorescence enhancement recognition and detection for Al³⁺ ions can be attributed to the coordination of Al³⁺ ions with N and O atoms on the COF-DHTA and the suppression of photoinduced electron transfer (PET). The results of the N₂ adsorption experiment, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation verified the coordination interaction between Al³⁺ ion and the N and O chelating sites on COF-DHTA. This work may pave the way to reasonable design fluorescent COF chemosensors for the recognition and detection of specific metal ions.