Geomimetic Interfacial Hydrothermal Synthesis of Crystalline Ionic Vinylene‐Linked Covalent Organic Frameworks

Ionic vinylene-linked covalent organic frameworks (ivCOFs) with ionic characteristics and highly conjugated structures have been promising functional materials. However, both the number of reported ionic vinylene-linked COFs and its synthetic methodologies still be limited. Herein, two new kinds of ionic vinylene-linked covalent organic frameworks (named as COF-NUC-1 and COF-NUC-2) are synthesized by novel geomimetic interfacial hydrothermal synthesis for the first time. Due to the insolubility of conjugated aldehyde monomers in water, a molecule/water interface is created, where the water-soluble N-ethyl-2,4,6-trimethylpyridinium bromide (ETMP-Br) can react with aldehyde monomers via the interface-confined Knoevenagel condensation reaction. The resultant ionic COFs show high crystallinity, high chemical stability, and hydrophilic nature. Benefiting from electron-withdrawing and redox properties of pyridinium salts, the as-fabricated memristor based on COF-NUC-1 film shows stable nonvolatile memory effects, featuring a high ON/OFF current ratio of 0.66 × 10³ and a small switch-on voltage of -0.68 V. This work expands the realm of ivCOFs and deepens the understanding of hydrothermal synthesis.