A Synthetic Route for Crystals of Woven Structures, Uniform Nanocrystals, and Thin Films of Imine Covalent Organic Frameworks

Developing synthetic
methodology to crystallize extended covalent
structures has been an important pursuit of reticular chemistry. Here,
we report a homogeneous synthetic route for imine covalent organic
frameworks (COFs) where crystallites emerge from clear solutions without
forming amorphous polyimine precipitates. The key feature of this
route is the utilization of tert-butyloxycarbonyl
group protected amine building blocks, which are deprotected in situ and gradually nucleate the crystalline framework.
We demonstrate the utility of this approach by crystallizing a woven
covalent organic framework (COF-112), in which covalent organic threads
are interlaced to form a three-dimensional woven framework. The homogeneous
imine COF synthesis also enabled the control of nucleation and crystal
growth leading to uniform nanocrystals, through microwave-assisted
reactions, and facile preparation of oriented thin films.