Flexible Hydrazone‐Linked Covalent Organic Frameworks With Enhanced Emission and Selective Nitroaromatic Sensing Performance

Covalent organic frameworks (COFs), with their highly ordered and extended π-conjugated architectures, offer great promise for the development of efficient solid-state luminescent materials. However, their photoluminescence is often hindered by aggregation-caused quenching (ACQ), limiting practical applications. To address this issue, we rationally designed and synthesized two novel hydrazone-linked COFs incorporating flexible vertex units into the backbone, thereby introducing structural flexibility. These COFs exhibit strong green emission in the solid state with high quantum yields approaching 20%, effectively mitigating ACQ effects. Moreover, the incorporation of abundant heteroatoms within the frameworks enables strong noncovalent interactions with electron-deficient nitroaromatic compounds, particularly 2,4,6-trinitrophenol (TNP), resulting in highly sensitive and selective fluorescence-based detection. This study demonstrates a viable strategy for enhancing the luminescent performance of COFs and expands their potential utility in chemical sensing and optoelectronic applications.