New strategies for the design and synthesis of novel covalent organic frameworks (COFs) and related materials

• Applicant: Dr. Alexander Schoedel
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 265423569

Covalent organic frameworks (COFs) represent a vastly emerging class of porous organic materials and have inspired the imagination of researchers due to their extra-large surface areas and very low density resulting in many potential applications. They are composed of organic molecular building blocks (MBBs) that are joined together by covalent bonds to form extended networks. After Yaghis seminal contributions on 2-D nets in 2005, COFs gained momentum since, in contrast to other well-known organic polymers, they impart desirable features such as porosity, crystallinity, low density and large surface areas among others. Most importantly, they can be designed by means of reticular chemistry from simple, high symmetry MBBs, a strategy which has already been proven fruitful in the design and synthesis of thousands of metal-organic frameworks (MOFs) over the past 20 years. In contrast to MOFs, COFs contain exclusively covalent rather than coordination bonds which generate superior performance materials in terms of thermal and chemical stability. However, the strength of the covalent bond considerably limits the synthesis of crystalline COF structures, since reversible reactions (dynamic bond formation and bond cleavage) would be required in order to obtain long range periodicity, i.e. crystallinity. Simply put, very robust materials were obtained through C-C coupling reactions as exemplified by the class of porous aromatic frameworks (PAFs) with no or very little crystallinity. On the other hand, very recently, the syntheses of large single crystal COFs were reported by introducing weak covalent bonding, which influences stability and led to non-porous materials. We propose herein to design and synthesize two newly discovered classes of covalent organic frameworks that are based upon hitherto unexplored binding motifs in the generation of extended networks. The divergent parameters of stability vs crystallinity are addressed through the development of two novel synthetic strategies to excerpt control over COF formation and yield predictable topological outcomes. In this context, we believe that well-established assembly strategies from supramolecular and coordination chemistry are uniquely suited to address this matter. This includes a recently developed stepwise assembly strategy as well as a route through hydrogen bond assisted networks, both of which are expected to generate novel classes in the realm of covalent organic frameworks and related materials.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Omar M. Yaghi