A Three-Dimensional sp2 Carbon-Conjugated Covalent Organic Framework

A first example of an sp2 carbon-conjugated three-dimensional (3D) covalent organic framework (COF) (BUCT-COF-4) is synthesized via the Knoevenagel condensation of the saddle-shaped aldehyde-substituted cyclooctatetrathiophene and 1,4-phenylenediacetonitrile. Ascribed to the extended π-conjugation and long-range ordered structures, BUCT-COF-4 displays high Hall electron mobility of 1.97 cm2 V–1 s–1 at room temperature. After it is doped with iodine, the material not only exhibits an enhanced electron mobility up to 2.62 cm2 V–1 s–1 in ambient air but also presents an unexpected metal-free ferromagnetic phase transition arising from the formation of aligned spins unidirectional across the whole sp2 carbon-conjugated 3D framework. This is the first report of a ferromagnetic phenomenon in 3D COF materials, which would broaden promising applications and open a new frontier in COF materials.本研究首次合成了一种sp²碳共轭三维共价有机框架（covalent organic framework, COF）材料BUCT-COF-4，该材料通过鞍形醛基取代环八四噻吩与1,4-苯二乙腈的克诺文格尔缩合反应合成。得益于拓展的π共轭体系与长程有序结构，BUCT-COF-4在室温下展现出高达1.97 cm² V⁻¹ s⁻¹的霍尔电子迁移率。经碘掺杂后，该材料不仅在常温空气中的电子迁移率提升至2.62 cm² V⁻¹ s⁻¹，还呈现出意外发现的无金属铁磁相变——该相变源于整个sp²碳共轭三维框架内形成的单向排列自旋。这是首次在三维共价有机框架材料中报道铁磁现象，该成果有望拓展该类材料的应用前景，并为共价有机框架材料的研究开辟全新前沿领域。