One stone, several birds: A carboxyl-carbazole-rich fluorescent covalent organic framework for the detection of tetrabromobisphenol S, Fe³ ⁺, ascorbic acid, D/L-arginine, and the removal of tetrabromobisphenol S

Considering the efficient utilization of resources and the simultaneous detection of multiple analytes, achieving selective detection of diverse analytes on one fluorescent covalent organic framework (COF) is of great significance. Herein, a carboxyl-carbazole-rich fluorescent COF (COF-DABT) was strategically synthesized using 3,6-diamino carbazole, capable of forming halogen bonds with analytes, and 2,5-bis(4′-formylphenyl) terephthalic acid, rich in carboxyl groups, which interacts with various analytes and adjusts fluorescence performance via its electron-withdrawing properties. The introduction of carbazole imparts fluorescence to COF-DABT through the intramolecular charge transfer (ICT) effect, while enabling selective fluorescence quenching. Specifically, the ICT of carbazole can be disrupted via linear halogen bond interactions with TBBPS, resulting in selectively detection of TBBPS in a fluorescence-off mode. Furthermore, efficient enrichment of TBBPS is facilitated by halogen bonds with carbazole and hydrogen bonds with carboxyl groups on COF-DABT. Selective fluorescence quenching of COF-DABT by Fe 3 + is achieved through chelating effect around carboxyl group, as well as cation-π interaction with carbazole benzene ring. This enables high selectivity detection of Fe 3+ via a fluorescence-off mode. Additionally, Fe 3+ can be reduced by ascorbic acid through REDOX reaction, mitigating interference with TBBPS detection and facilitating fluorescence-off-on mode detection of AA. Besides, rich carboxyl groups on COF-DABT exert a negative regulatory effect on the carbazole ICT mechanism. To counter this, D/L-Arg, with a size complementary to the adjacent carboxyl groups on COF-DABT, is introduced. Hydrogen bond interactions between D/L-Arg and carboxyl groups reduce the negative regulatory effect, allowing fluorescence enhancement for highly selective detection of D/L-Arg. Through rational design and functional optimization of fluorescent COF structures, multi-mode detection methods enable simultaneous detection of different analytes, achieving the goal of "one stone, several birds."