3D Cage COFs: A Dynamic Three-Dimensional Covalent Organic Framework with High-Connectivity Organic Cage Nodes

Abstract

Three-dimensional (3D) covalent organic frameworks (COFs) are rare because there is a limited choice of organic building blocks that offer multiple reactive sites in a polyhedral geometry. Here, we synthesized an organic cage molecule (<b>Cage-6-NH</b>_<b>2</b>) that was used as a triangular prism node to yield the first cage-based 3D COF, <b>3D-CageCOF-1</b>. This COF adopts an unreported 2-fold interpenetrated <b>acs</b> topology and exhibits reversible dynamic behavior, switching between a small-pore (<b>sp</b>) structure and a large-pore (<b>lp</b>) structure. It also shows high CO₂ uptake and captures water at low humidity (<40%). This demonstrates the potential for expanding the structural complexity of 3D COFs by using organic cages as the building units.