Catalyst-derived hierarchy in 2D imine-based covalent organic frameworks

Identifying facile strategies for hierarchically structuring crystalline porous materials is critical for realizing diffusion length scales suitable for broad applications. Here, we elucidate synthesis-structure-function relations governing how room temperature catalytic conditions can be exploited to tune covalent organic framework (COF) growth and thereby access unique hierarchical morphologies without the need to introduce secondary templates or structure directing molecules. Specifically, we demonstrate how scandium triflate, an efficient catalyst involved in the synthesis of imine-based COFs, can be exploited as an effective growth modifier capable of selectively titrating terminal amines on 2D COF layers to facilitate anisotropic crystal growth. We systematically map a compositional pseudo-phase space and uncover key mechanistic insights governing the catalyst-derived evolution of globular COFs with sub-micron diffusion length scales into unique rosette structures. Comprised of interconnected, high-aspect-ratio crystalline porous sheets of only several unit cells in thickness, the resulting COFs offer orders of magnitude reduction in diffusion length scales and several-fold increase in external surface area, enabling rapid uptake of bulky dyes. Generally, the resulting synthesis-structure-function relations hold promise for realizing unique control over COF mesostructure, morphology, and function.