Rapid Formation of Vinylene-Linked Covalent Organic Frameworks Promoted by Dipole Moment

Abstract

Vinylene-linked covalent organic frameworks (COFs) are typically prepared via the Knoevenagel reaction under acid- or base-catalyzed solvothermal or benzoic anhydride-catalyzed solid-state conditions under reaction times spanning from 3 to 5 days. Herein, we show that the incorporation of a dipole moment into the COF building block accelerates the formation of ordered material. Under solvent-free Knoevenagel conditions, 3,8-dimethyl-4,7-phenanthroline (Phen) in combination with C3-symmetric aldehydes gives access to ordered hexagonal vinylene-linked COFs. A detailed study using triformylbenzene as counterpart evidences the formation of crystalline framework within hours. Theoretical and experimental studies indicate that the fast formation stems from favorable intermolecular interactions of the π-extended Phen building block due to the presence of a dipole moment, which also endows the material with excellent mechanical stability under ball milling. In addition, all prepared materials exhibited broad visible light absorption and narrow band gap energies of ≤2.48 eV and revealed photocatalytic activity for the degradation of dyes.