Pre‐Crosslinked Network‐Mediated Dual Exchange Enables Boosting Chiroptical Activity and Decoupled Two‐Level Chirality in Covalent Organic Frameworks

ABSTRACT

The construction of crystalline covalent organic frameworks (COFs) with strong and tunable chiroptical responses remains challenging due to rapid crystallization that limits effective chirality induction. Here, we report a pre‐crosslinked network‐mediated dual‐exchange strategy that enables both amplified chiroptical activity and decoupled multilevel chirality in β‐ketoenamine‐linked COFs. In this approach, monomers are first immobilized within a pre‐crosslinked amorphous imine network, which kinetically regulates subsequent framework formation. The crystallization proceeds through a dual‐exchange process involving concurrent amine and aldehyde exchange, thereby retarding reaction kinetics and prolonging the chirality induction window. As a result, the obtained COFs exhibit pronounced propeller‐like conformational chirality with dissymmetry factors (| g _abs |) up to 0.071, representing an order‐of‐magnitude enhancement over conventional systems. Furthermore, by integrating supramolecular transcription, mesoscopic helicity and molecular chirality are decoupled and independently incorporated within a single framework. Their cooperative or antagonistic interplay leads to enhanced or attenuated chiroptical responses. This work provides a general strategy for boosting chiroptical activity and programming multilevel chirality in crystalline frameworks.