Aqueous synthesis of three-dimensional helical covalent organic frameworks with hierarchical chirality

Analogous to the multilevel structure of proteins, hierarchical chiral materials have attracted much attention due to their excellent optical activity. Among them, covalent organic frameworks (COFs) with two-dimensional (2D) or three-dimensional (3D) topologies have become ideal platforms for integrating hierarchical chirality due to their modular and tunable building block. However, limited by the inherent complexity of the structure of 3D COFs, studies on their hierarchical chirality, especially helical geometry chirality, are still scarce. Herein, we report a strategy to obtain helical 3D COFs using chiral surfactants as templates in aqueous phase. The weak interactions including hydrogen bonds and electrostatic interactions between surfactants and precursors simultaneously facilitated helical curl and self-correcting crystallization of the ribbon-like precursors, resulting in the synthesis of 3D helical hierarchical chiral COFs. Notably, the chiral centers of the surfactants provide a guiding mechanism that contributes to the COFs achieving a high enantiomerically purity up to 85 %.