Dual Role of Ligand for Porphyrin-Based Covalent Organic Framework Exfoliation and Turn-Up Fluorescence Sensing

Covalent organic nanosheets (CONs) have been attracting widespread attention; however, their fabrication remains challenging owing to their uncontrollable thickness, multilayer structure, and low yield. Herein, we report a ligand that simultaneously achieves porphyrin covalent organic framework (COF) exfoliation and “turn-up” fluorescence sensing. By introducing aniline as the axial ligand and coordinating it to porphyrin COF, uniform nanosheets with 6–10 layers were obtained that exhibited 28 times greater fluorescence for aniline than the pristine COF owing to a synergistic effect. This work not only paves the way to utilize COF to realize highly efficient turn-up fluorescent sensing of aniline but also provides a strategy to make thin-layer nanosheets.