Robust Mesoporous Functional Hydrogen-Bonded Organic Framework for Hypochlorite Detection

Although tremendous progress has been achieved in the field of hydrogen-bonded organic frameworks (HOFs), the low stability, small/none pores, and difficult functionality severely obstruct their development. Herein, a novel robust mesoporous HOF (HOF-FAFU-1) decorated with a high density of free hydroxy moieties has been designed and readily synthesized in the de novo synthesis. In HOF-FAFU-1, the planar building blocks are connected to each other by typical intermolecular carboxylate dimers to form two-dimensional (2D) layers with sql topology, which are further connected to their adjacent layers by face-to-face π-π interactions to obtain a three-dimensional (3D) open mesoporous framework. Owing to the high density of intermolecular hydrogen bonding and strong π-π interactions, HOF-FAFU-1 is very stable, allowing it to retain its structure in aqueous solutions with a pH range of 1-9. Benefiting from the decorated hydroxy moieties, HOF-FAFU-1 was exploited as a fluorescent sensor for hypochlorite detection in water media by a turn-off mode, which cannot be realized by its nonhydroxy groups anchoring counterpart (HOF-TCBP). The proposed sensing system is highly efficient, validated by a very broad linear range (0-0.45 mM), fast response (15 s), and small limit of detection (LOD) (1.32 μM). The fluorescent quenching of HOF-FAFU-1 toward hypochlorite was also investigated, mainly being ascribed to the transformation of building blocks from the fluorescent reduced state to the nonfluorescent oxidative state. This work not only demonstrates that HOFs integrated with high stability and large pores as well as high density of functional groups can be simultaneously realized by judicious design of building blocks but also conceptually elucidates that such HOFs can effectively extend the application fields of HOFs.