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.

Keywords

AIE and ESIPT / antibiotic sensing / covalent organic framework / fluorescence reference / non-coplanar linkers

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