All sp2 carbon covalent organic frameworks

Covalent organic frameworks (COFs) are a class of crystalline polymers that integrate organic units into 2D and 3D skeletons to achieve ordered yet extended structures via topology-directed polymerization. Recent progress in chemistry over the past 4 years has greatly raised the ability to design the frameworks to attain fully π-conjugated all sp2 carbon structures. In this Opinion article, we summarize the chemistry to explore sp2 carbon frameworks by highlighting their design principles and synthetic strategies to show the structural scope and diversity. We scrutinize the properties and functions of sp2 carbon frameworks to elucidate their structural origins. We predict key fundamental issues for sp2 carbon frameworks and future directions from chemistry, physics, and materials perspectives.