Phenyl/Perfluorophenyl Stacking Interactions Enhance Structural Order in Two-Dimensional Covalent Organic Frameworks

A two-dimensional imine-based covalent organic framework (COF) was designed and synthesized such that phenyl and perfluorophenyl structural units can seamlessly alternate between layers of the framework. X-ray diffraction of the COF powders reveals a striking increase in crystallinity for the COF with self-complementary phenyl/perfluorophenyl interactions (FASt-COF). Whereas measured values of the Brunauer–Emmet–Teller (BET) surface areas for the nonfluorinated Base-COF and the COF employing hydrogen bonding were ∼37% and 59%, respectively, of their theoretical Connolly surface areas, the BET value for FASt-COF achieves >90% of its theoretical value (∼1700 m2/g). Transmission electron microscopy images also revealed unique micron-sized rodlike features in FASt-COF that were not present in the other materials. The results highlight a promising approach for improving surface areas and long-range order in two-dimensional COFs.