Breaking π-π Stacking in One-Dimensional Covalent Organic Frameworks

Covalent organic frameworks (COFs) constructed from aromatic building blocks typically incorporate specific functional groups to achieve target properties; however, the active role of intrinsic aromatic backbones remains underexplored due to their limited accessibility usually imposed by interlayer π-π stacking. Herein, we report a steric-hindrance-driven breaking of interlayer π-π stacking in one-dimensional (1D) COFs built from sterically enforced non-coplanar monomers, thereby rendering the accessibility of aromatic domains and enabling superior adsorption performance, as exemplified by I₂ uptake. Two COFs, TFPE-MDA, and TFPB-MDA, are assembled via interlayer van der Waals stacking, where the aromatic moieties orient toward the pore channels exposing the backbone π electrons; electron population analysis verifies that this packing does not perturb the π-electron distribution. Iodine-vapor adsorption measurements show high I₂ uptake capacities of 4.80 and 5.61 g·g^-1 for TFPE-MDA and TFPB-MDA, respectively. FTIR, Raman, and XPS characterizations combined with theoretical calculations confirm I···π interactions between I₂ and the accessible π electrons of aromatic moieties in the COF frameworks. This study provides a novel design strategy for high-performance COF materials by utilizing sterically enforced non-coplanar monomers for breaking the commonly observed interlayer π-π stacking, thus enabling the access and utilization of the intrinsic π electrons in COF backbones.