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

Abstract

AbstractA new imine‐linked covalent organic framework (COFDHA‐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 COFDHA‐TAPB to restrict intramolecular rotations. Hydrogen bonds are also formed between different layers of COFDHA‐TAPB, which further restricts supramolecular rotation by narrowing the layer spacing. Moreover, the COFDHA‐TAPB exhibits a hollow sphere structure, which also reduces ACQ and intramolecular rotation. Therefore, COFDHA‐TAPB has a strong emission peak at 408 nm, which is used for nitrofurazone detection. The detection linear range is 0.33 µm–0.197 mm (0.066–39 µg mL−1), and the detection limit is 0.11 µm (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.