Tessellated multiporous two-dimensional covalent organic frameworks

In the past decade, covalent organic frameworks (COFs) have emerged as a new class of highly ordered crystalline organic porous polymers. They have attracted tremendous research interest because of their unique structures and potential applications in gas storage and separation, energy storage, catalysis and optoelectronic materials development. Although the skeletons and pore structures of COFs are customizable through judicious selection of chemical building blocks, COF materials have been mainly limited to uniform pore structures with homogeneous pore environments. Two-dimensional COFs with complex multipore structures are largely unexplored, perhaps owing to the challenges that are inherent in designing selective syntheses. Simple tessellation has been remarkably successful in the preparation of regular 2D COFs, but building multiporous systems requires the aid of mathematical design. In this Perspective, we discuss four different approaches to tessellated 2D COFS with a focus on the mathematical rules for their application. A comparison of these strategies should provide guidance to those designing new applications of COF materials. Covalent organic frameworks (COFs) have potential applications in, for example, gas storage and separation. The pore sizes in these materials are tunable by selection of the building blocks, and materials with multiple pore sizes are desirable. This Perspective considers synthetic approaches to 2D COFs that rely on tessellation to prepare such multiporous materials.