Interlocked 2D Covalent Organic Frameworks from Overcrowded Nodes

A challenging aspect in the synthesis of covalent organic frameworks (COFs) that goes beyond the framework's structure and topology is interpenetration, where two or more independent frameworks are mechanically interlocked with each other. Such interpenetrated or interlocked frameworks are commonly found in three-dimensional (3D) COFs with large pores. However, interlocked two-dimensional (2D) COFs are rarely seen in the literature, as 2D COF layers typically crystallize in stacks that maximize stabilization through π-stacking. The few interlocked 2D COFs described to date have been derived from monomers with aryl groups arranged perpendicularly. Herein, we report an interlocked 2D COF derived from a new class of monomers constituted of sterically overcrowded polycyclic aromatic hydrocarbons. The formation of such an interlocked structure is ascribed to the presence and the bulkiness of the substituents that directly interfere with interlayer π-stacking. The microscopy, gas sorption, spectroscopic, and charge transport characterization are consistent with the absence of π-stacking, as imposed by the interlocked architecture. This work evidences how the use of overcrowded aromatic systems as monomers can generate mechanically interlocked 2D COFs, offering new avenues for the design of COFs with unconventional topologies.