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.
Material synthesis and characterization was supported by BASF SE (Ludwigshafen, Germany) and King Abdulaziz City for Science and Technology as part of a joint KACST–UC Berkeley collaboration (Center of Excellence for Nanomaterials and Clean Energy Applications). Work performed at the Advanced Light Source (beamline 7.3.3 and 11.3.1) and at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract no. DE-AC02-05CH11231. We also acknowledge the Kavli energy nanoscience institute at UC Berkeley for support of research on nanostructuring of reticular materials. Y.M. and O.T. acknowledge support from ShanghaiTech Startup Funding and Shanghai Science and Technology Committee (17ZR1418600), Y.Z. acknowledges support from a SIP fellowship. L.G. acknowledges support from the Army Research Office for the Multidisciplinary University Research Initiatives award WG11NF-15-1-0047. F.G. acknowledges the Spanish Ministry of Economy and Competitiveness for funding through the Ramón y Cajal program.