Large Multichannel Architectures in Three-Dimensional Covalent Organic Frameworks for Efficient Guest Diffusion

Abstract

Guest diffusion in bulk covalent organic frameworks (COFs) is fundamentally limited by misaligned layers in two-dimensional (2D) frameworks and discontinuous 1D channels in 2D and 3D COFs across crystallite boundaries. Here, we report new triptycene-based 3D COFs, HKU-2-PEGn (HKU: The University of Hong Kong; n = 2 or 4), featuring orthogonally interconnected channels and tunable polyethylene glycol (PEG) functionality that mitigate the diffusion limitations. These COFs contain channels up to 4.8 nm in width and a total of 67 channels larger than 5 & Aring; (13 crystallographically unique) distributed along multiple crystallographic directions, facilitating channel connectivity between randomly oriented crystallites. Lithium-ion (Li+) transport in bulk samples of these COFs exhibits high diffusion coefficients across a wide range of Li+ concentrations, comparable to those of commercial liquid electrolytes, demonstrating that large, multichannel crystalline architectures effectively mitigate the diffusion anisotropy inherent to low-dimensional channels in COFs.