Vinylene-Linking of Polycyclic Aromatic Hydrocarbons to π-Extended Two-Dimensional Covalent Organic Framework Photocatalyst for HO Synthesis.

Polycyclic aromatic hydrocarbons (PAHs) hold the predominant role either as individual molecules or building blocks in the field of organic semiconductors or nanocarbons. Connecting PAHs via sp-carbon bridges to form high-crystalline π-extended structures is highly desired not only for enlarging the regimes of two-dimensional materials but also for achieving exceptional properties/functions. In this work, we developed 5,10-dimethyl-4,9-diazapyrene as a key monomer, whose two methyl groups at the positions adjacent to nitrogen atoms, can helpfully increase the solubility, and serve as the active connection sites. In the presence of organic acids, this monomer enables smoothly conducting Knoevenagel condensation to form two vinylene-linked PAH-cored COFs, which show high-crystalline honeycomb structures with large surface areas up to 1238 m g. Owing to the direct connection mode of PAH building blocks with vinylene, the as-prepared COFs possess spatially extended π-conjugation and substantial semiconducting properties. Consequently, their visible-light photocatalysis with exceptional activity and durability was manifested to generate HO up to 3820 μmol g h in pure water, and even 17080 μmol g h using benzyl alcohol as a hole sacrificial agent.