Emissive Covalent Organic Frameworks: Fluorescence Improvement via a Controllable Vertex Strategy and Chemical Sensing

Creating highly emissive covalent organic frameworks (COFs) has traditionally been difficult, owing to strong π–π interactions between adjacent layers, resulting in aggregation-caused quenching properties. In this article, we report the use of a vertex strategy to create emissive COFs with enhanced fluorescence performances. This strategy involved introducing different vertex units into the COF structure. These vertex units including different N atoms possessed p orbital lone pairs of electrons, which formed p−π conjugation between the linkages and the walls of the COFs. The p−π conjugation from the linkages to the walls effectively suppressed the fluorescence quenching effect in COFs, leading to the development of COFs with strong emission properties. The designed emissive COFs were evaluated for their ability to detect 2,4,6-trinitrophenol, a specific type of nitro-explosive, in water. These COFs demonstrated high sensitivity and selectivity for 2,4,6-trinitrophenol detection compared to other nitro-explosives. In summary, the controllable vertex strategy is a promising method for designing emissive COFs and enhancing their fluorescence properties, paving the way for the development of luminescent materials with diverse applications.