Catalyst-free solid-state cross-linking of covalent organic frameworks in confined space

A “confined space” provides a unique environment to regulate the crystallization thermodynamics and kinetics by confining the reactants in the restricted space dimensions. Solid-state crystal-to-crystal transitions in confined space are controlled by the preassembly of molecules in a crystal lattice and occur inside the lattice. Herein, we report the first case of construction of crystalline cross-linked covalent organic frameworks (CL-COFs) through solid-state cross-linking of acetylenic groups-bridged 2D COFs in spatially limited systems. Specifically, this transformation is thermally induced, yielding CL-COFs with superlative properties, including outstanding enhancement in crystallinity, specific surface area, and stability. We further demonstrate the CL-COFs as high conductivity polymers after iodine doping. This work underscores the opportunity to use lattice-constrained solid-state cross-linking to develop more versatile and feature-rich polyacetylene networks.