Emissive covalent organic frameworks with abundant interaction sites for hydrazine sensing†

Covalent organic frameworks (COFs) possess versatile advantages, including their lightweight nature, exceptional stability, and having a well-defined π structure, rending them highly promising for fluorescence sensors. One of the most important factors for sensing is the presence of interaction sites, which previous research has not considered extensively. In this study, we present the synthesis of two emissive hydrazone-linked COFs (EH-COFs) under solvothermal conditions. The hydrazone linkages, which contain –NH single bond groups on the walls, reduce aggregation-caused fluorescence quenching, resulting in enhanced emission activity. Furthermore, the abundance of interaction sites (nitrogen and oxygen atoms) on the walls enables efficient interaction with guest molecules. Owing to these advantages, EH-COFs exhibited elevated sensitivity and selectivity, with low detection limits, for hydrazine sensing, ranking them among the top-performing fluorescence probes reported to date.