Linker‐regulated Imine‐based Covalent Organic Frameworks Enable Dual‐Mode Fluorescence Emission as Stable Internal Reference Signal

ABSTRACT Energy dissipation caused by π–π stacking and bond rotation has long hindered the practical application of imine‐based covalent organic frameworks (COFs) in the optical field. In this study, we constructed a class of COFs with dual‐mode fluorescence emission, overcoming the intrinsically low fluorescence efficiency limitations of imine‐based COFs. The non‐coplanar linker molecules endow the novel COFs with aggregation‐induced emission effects. Furthermore, the enol‐keto tautomerism generated during COFs synthesis not only restricted bond rotation but also induced excited‐state intramolecular proton transfer, further enhancing fluorescence output. Through the combined action of these two luminescent modes, the obtained imine‐based COF‐2 and COF‐3 exhibited high quantum yields of reaching 10.7% and 13.1%, respectively. The broad photoexcitation range and intense fluorescence emission provide a stable internal reference during detection, reducing signal interference from environmental variations. Combined with the sensitized luminescence produced by rare earth ions on antibiotics, a new ratiometric probe can be constructed to detect trace amounts of antibiotics in water. This work presents a new strategy for designing fluorescent imine‐based COFs, promoting their potential application in the field of luminescent sensing.