Optimizing the Stability of Imine-linked 3D Covalent Organic Frameworks through Room Temperature Growth

Covalent Organic Frameworks (COFs) are a class of crystalline porous polymers with well-defined molecular structures derived from their rigid starting materials. The overall mechanism for the formation of COFs is not readily understood at this point and there are many challenges such as the long-term stability of the material that prevent the approach from being broadly incorporated into applications. This material has the potential to be used in desalination to address the increasing issue of water scarcity. To establish 3D COFs as a viable scaffold material in water treatment, fundamental synthetic challenges must be overcome. In the case of two imine-linked systems, COF-300 and COF-320, the porous network can distort and collapse under aqueous conditions, decreasing the accessible surface area. Moreover, a facile method to orthogonally functionalize 3D COFs has not yet been established. In our studies, I have identified multi-step synthetic methods that preferentially generate the porous form of COF-300 via an intermediate state. Here I describe our multi-stage synthetic approach and methods that yield highly stable 3D COFs. This study also examines the early stages of the 3D COF growth through room temperature studies. I have discovered that room temperature samples prepared for various amounts of time are able to nucleate the crystalline porous material structure. The regrowth of these samples at high temperature then continues the growth of these seeds into highly crystalline material. By leveraging this novel mechanistic understanding, a porous COF-300 material was formed that remained stable for over three months. This room temperature methodology was successful for the COF-320 system as well