Narrow‐Pore Engineering of Vinylene‐Linked Covalent Organic Frameworks with Weak Interaction‐Triggered Multiple Responses

Abstract

AbstractVinylene‐linked covalent organic frameworks (COFs) are emerging as promising crystalline materials, but their narrow pore engineering is severely impeded by the weak reversibility of the carbon‐carbon double bond formation reaction, which has led to less exploration of their ultramicroporous structures and properties. Herein, we developed a single aromatic ring‐based tetratopic monomer, tetramethylpyrazine, which undergoes a smooth Knoevenegal condensation at its four arylmethly carbon atoms with linear aromatic dialdehyde monomers upon the self‐catalyzed activation of pyridine nitrogen‐containing monomers in the presence of an organic anhydride. This has resulted in the formation of two vinylene‐linked COFs, which both crystallized in orthorhombic lattices, and layered in AA stacking fashions along the vertical directions. They exhibit high surface areas and well‐tailored ultramicropore sizes up to 0.5 nm. The unique cross‐linking mode at two pairs of para‐positions of each pyrazine unit through carbon‐carbon double bonds afford them with π‐extended conjugation over the in‐plane backbones and substantial semiconducting characters. The resultant COFs can be well‐dispersed in water to form stable sub‐microparticles with negative charges (zeta potentials: ca. −30 mV), and exhibiting tunable aggregation behaviors through protonation/deprotonation. As a consequence, they exhibit pore‐size‐dependent colorimetric responses to various anions with different pKa values in high selectivity.