Vinylene‐Linked Covalent Organic Frameworks With Multi‐Intramolecular Coupling‐Promoted Photocatalytic CO 2 ‐to‐CO Conversion

Abstract

ABSTRACT Covalent organic frameworks (COFs) offer significant potential for solar energy conversion, but their sluggish intrinsic charge‐transfer kinetics inherently restrict the activation of stable CO 2 . Herein, we developed a new electron‐deficient monomer 6,6′‐dimethyl‐3,3′‐bipyridazine (DPz), which can undergo Knoevenagel condensation with triformyl polyphenylenes to construct a new type of π‐conjugated COFs. Their in‐plane backbones are patterned with a repeated donor‐π‐acceptor–acceptor‐π‐donor (D‐π‐A–A‐π‐D) moiety by vinylene‐linking of a bipyridazine core with two (bi‐)phenyl terminals, which are vertically packed into a hexagonal lattice in an AA‐stacking mode, yielding high specific surface areas and well‐defined nanochannels. The quadrupolar structure strengthened by bipyridazine as the dual acceptors, endowed these COFs with exceptional semiconducting performance. In particular, analysis of femtosecond transient absorption (fs‐TA) spectra revealed outstanding intramolecular charge transfer. Meanwhile, the substantial 1,2‐diazine units might dominate either the highest occupied molecular orbital or lowest unoccupied molecular orbital energy levels of these COFs, thereby promoting hybrid orbital‐coupled electron transfer, as also evaluated by theoretical calculations. Accordingly, the neat as‐prepared COFs exhibit promising photoinduced charge‐transfer dynamics. Using [Ru(bpy) 3 ]Cl 2 as a photosensitizer, the system achieved CO production rates of up to 1594 µmol g − 1 h − 1 , with a selectivity of more than 97%, among the highest values for all COF‐based photocatalysts reported to date.