Constructing a three-in-one light-responsive covalent organic framework with enhanced performance through post-synthetic modification: Versatile fluorescence sensing, colorimetric detection, and adsorption of mesotrione

Covalent organic frameworks (COFs) have been widely investigated owing to their tunable structures and multifunctionality, with pore engineering further enhancing their physicochemical properties. Herein, a hydroxyl-functionalized COF (PyTFPB-OH) was synthesized via solvothermal condensation of 5′-(4-formyl-3-hydroxyphenyl)-3,3″-dihydroxy-[1,1′:3′,1″-terphenyl]-4,4″-dicarbaldehyde (TFPB-OH) and 4,4′,4″,4″‘-(pyrene-1,3,6,8-tetrayl)tetraaniline (Py), followed by post-synthetic modification (PSM) under mild conditions to incorporate azo units, yielding PyTFPB-azo. Comprehensive characterization confirmed the successful PSM, with the introduced azo units significantly enhancing multifunctionality. In terms of detection, the modified COF retained intrinsic fluorescence while exhibiting enhanced oxidase-like activity, enabling dual-mode detection of the herbicide mesotrione (MST) through fluorescence (LOD of 0.168 μM) and colorimetry (LOD of 0.038 μM) modalities. Importantly, the inherent synergy between these two detection modalities allowed for self-calibration, improving the accuracy and reliability of MST quantification. Furthermore, photoinduced trans -to- cis isomerization of azo units under 365 nm irradiation modulated pore environments, increasing MST adsorption efficiency through strengthened substrate interactions. Overall, this work establishes a multifunctional platform combining sensing and adsorption capabilities, alongside an effective PSM strategy to optimize metal-free COF-based nanozyme design.