Synthesis of single-crystalline sp2-carbon-linked covalent organic frameworks through imine-to-olefin transformation

sp²-carbon-linked covalent organic frameworks (sp²c-COFs) are crystalline porous polymers with repeat organic units linked by sp² carbons, and have attracted increasing interest due to their robust skeleton and tunable semiconducting properties. Single-crystalline sp²c-COFs with well-defined structures can represent an ideal platform for investigating fundamental physics properties and device performance. However, the robust olefin bonds inhibit the reversible-reaction-based crystal self-correction, thus yielding polycrystalline or amorphous polymers. Here we report an imine-to-olefin transformation strategy to form single-crystal sp²c-COFs. The isolated single crystals display rectangular nanotube-like domains with sizes up to approximately 24 μm × 0.8 μm × 0.8 μm, and permanent pore distribution around 1.1 nm. The highly conjugated olefin linkage endows the crystals with enhanced electronic connectivity which determines a remarkable room-temperature metal-free ferromagnetism (8.6 × 10⁻³ emu g⁻¹). Our protocol is robust and generally applicable for the synthesis of single-crystalline sp²c-COFs for future spin-electron devices.