Construction of a Hollow Spherical Covalent Organic Framework with Olefin and Imine Dual Linkages Based on Orthogonal Reactions

Covalent organic frameworks (COFs) have widespread applications in many fields. However, successful attempts to construct COFs through the formation of two types of covalent bonds remain limited and challengeable. Here, we report the first example of a COF with olefin and imine dual linkages, which was enabled by orthogonal Schiff base reaction and the Knoevenagel condensation. The obtained COF-FD1 exhibits good stability and high selectivity in the fluorescence sensing of Fe3+ ions. Remarkably, this COF features a relatively rare hollow spherical morphology, and a time-dependent study of the continuous transformation from initial solid spherical to hollow spherical structures reveals an Ostwald ripening mechanism. This research not only demonstrates a new approach for the design and synthesis of COFs with dual linkages but also may bring about the possibility of constructing COFs with hollow structures.