A Stable Luminescent Covalent Organic Framework Nanosheet for Sensitive Molecular Recognition

Despite rapid advances in fluorescence detectors over the past decade, the development of a highly stable, sensitive, and selective fluorescence platform for molecular recognition remains a considerable challenge. Here we report a stable carbazole-based sp2 carbon fluorescence covalent organic framework (COF) nanosheet, termed a JUC-557 nanosheet. Owing to the synergistic effect of aggregation-induced emission-and aggregation-caused quenching-based chromophores, the architecture of the JUC-577 shows high absolute quantum yields (up to 23.0%) in the solid state and when dispersed in various solvents as well as excellent sensing performance toward specific analytes, such as iodine (Ka: 2.10 x 105 M-1 and LOD: 302 ppb), 2,4,6 -trinitrotoluene (Ka: 4.38 x 105 M-1 and LOD: 129 ppb), and especially nitrobenzene (Ka: 6.18 x 106 M-1 and LOD: 5 ppb) that is superior to that of fluorescence detection materials reported so far. Furthermore, the JUC-557 nanosheet preserves strong luminescence and sensitive recognition, even under harsh conditions, and allows trace detection of various analytes via a handheld UV lamp. These findings pave the way for developing stable ultrathin COF nanomaterials for highly sensitive and selective molecular detection.