Designing Fluorescent Covalent Organic Frameworks by Controlling Layer Spacing, Size of Aromatic Linker and Side Chains for Detection of Nitrofurazone

Abstract A new imine‐linked covalent organic framework (COF DHA‐TAPB ) with strong fluorescence is designed by using 2,5‐dihydroxybenzaldehyde (DHA) and 1,3,5‐tri(4‐aminophenyl)benzene (TAPB) as monomers. The TAPB has a suitable aromatic skeleton in which slight distortion between phenyl groups reduces aggregation‐caused quenching (ACQ). The hydroxyl group side chains of DHA form hydrogen bond with the imine bonds of COF DHA‐TAPB to restrict intramolecular rotations. Hydrogen bonds are also formed between different layers of COF DHA‐TAPB , which further restricts supramolecular rotation by narrowing the layer spacing. Moreover, the COF DHA‐TAPB exhibits a hollow sphere structure, which also reduces ACQ and intramolecular rotation. Therefore, COF DHA‐TAPB has a strong emission peak at 408 nm, which is used for nitrofurazone detection. The detection linear range is 0.33 µ m –0.197 m m (0.066–39 µg mL −1 ), and the detection limit is 0.11 µ m (0.022 µg mL −1 ). This work also provides an important guideline to design strongly fluorescent covalent organic framework by controlling layer spacing, aromatic linkers sizes and side chains of monomers for sensors.