Structural and Dimensional Transformations between Covalent Organic Frameworks via Linker Exchange

Covalent organic frameworks (COFs) are porous crystalline materials with well-controlled structures and extensive potential applications. However, construction of new COFs has tremendous challenges including design and synthesis of building block monomers, selection of reaction solvent systems, and investigation of reaction time and temperature. Here, we performed the structural transformation in the three-dimensional (3D) COFs (COF-300 and COF-320) and dimensional transformation from 3D (COF-301) to 2D (TPB-DHTP-COF) via the dynamic covalent chemistry principle, and the successful realization of these exchanges was confirmed by FT-IR, 1H NMR, PXRD, and nitrogen sorption isotherm measurements. Based on the results of PXRD patterns and 1H NMR spectra, the COF-320-to-COF-300 transformation was successfully achieved, and an efficiency as high as 89% was attained. A new network structure rather than COF-320 was obtained after transformation in the opposite direction (from COF-300 to COF-320), which contains the two aldehyde building units biphenyl-4,4′-dicarbaldehyde (BPDA) and terephthaldehyde (TA) in one framework. Meanwhile, the dimensional transformation of COFs with 78% exchange efficiency for COF-301-to-TPB-DHTP-COF is also achieved. These results not only reveal the COF-to-COF transformation in 3D-to-3D and 3D-to-2D but also provide a new way for constructing new COFs that is difficult to synthesize in one step.