UC Berkeley

The reticular synthesis of covalent organic frameworks (COFs), extended porous two-dimensional (2D) or three-dimensional (3D) networks held together by strong, highly directional chemical bonds, has thus far been restricted to small, shape-persistent, molecular building blocks. Here, we demonstrate the growth of crystalline 2D COFs from a polydisperse macromolecule derived from single-layer graphene, bottom-up synthesized quasi-one-dimensional (1D) graphene nanoribbons (GNRs). X-ray scattering and transmission electron microscopy reveal that 2D sheets of GNR-COFs self-assembled at a liquid-liquid interface stack parallel to the layer boundary and exhibit an orthotropic crystal packing. Liquid-phase exfoliation of multilayer GNR-COF crystals gives access to large-area (>105 nm2) bilayer and trilayer cGNR-COF films. The functional integration of extended 1D materials into crystalline COFs greatly expands the structural complexity and the scope of mechanical and physical materials properties accessible through a deterministic reticular bottom-up approach.