Self-Assembly of Helical Nanofibrous Chiral Covalent Organic Frameworks

Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well-defined one-handed double-helical nanofibrous morphologies were constructed via an unprecedented template-free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time-dependent experiments reveal the spontaneous transformation of initial rod-like aggregates into the double-helical microstructures. We have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor (g(lum)) up to approximate to 0.01.

Automated summary

Two chiral covalent organic frameworks (COFs) with well-defined one-handed double-helical nanofibrous morphologies were successfully constructed using a template-free method based on the diastereoselective formation of aminal linkages. Time-dependent experiments revealed the spontaneous transformation of initial rod-like aggregates into the double-helical microstructures. The helical chirality and circular dichroism signal can be easily reversed by adjusting the amount of acetic acid during synthesis. Furthermore, the helical COF nanostructures were able to induce circularly polarized luminescence with a high luminescent asymmetric factor (g(lum)) of approximately 0.01 by transferring chirality to achiral fluorescent molecular adsorbents.