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.
Although π‐conjugated two dimensional (2D) covalent organic frameworks (COFs) have been extensively reported, developing fully π‐conjugated 3D COFs is still an extremely difficult problem due to the lack of fully π‐conjugated 3D linkers. We synthesize a fully conjugated 3D COF (BUCT‐COF‐1) by designing a saddle‐shaped building block of aldehyde‐substituted cyclooctatetrathiophene (COThP)‐CHO. As a consequence of the fully conjugated 3D network, BUCT‐COF‐1 demonstrates ultrahigh Hall electron mobility up to ≈3.0 cm2 V−1 s−1 at room temperature, which is one order of magnitude higher than the current π‐conjugated 2D COFs. Temperature‐dependent conductivity measurements reveal that the charge carriers in BUCT‐ COF‐1 exhibit the band‐like transport mechanism, which is entirely different from the hopping transport phenomena observed in common organic materials. The findings indicate that fully conjugated 3D COFs can achieve electron delocalization and charge‐transport pathways within the whole 3D skeleton, which may open up a new frontier in the design of organic semiconducting materials.
Although π‐conjugated two dimensional (2D) covalent organic frameworks (COFs) have been extensively reported, developing fully π‐conjugated 3D COFs is still an extremely difficult problem due to the lack of fully π‐conjugated 3D linkers. We synthesize a fully conjugated 3D COF (BUCT‐COF‐1) by designing a saddle‐shaped building block of aldehyde‐substituted cyclooctatetrathiophene (COThP)‐CHO. As a consequence of the fully conjugated 3D network, BUCT‐COF‐1 demonstrates ultrahigh Hall electron mobility up to ≈3.0 cm2 V−1 s−1 at room temperature, which is one order of magnitude higher than the current π‐conjugated 2D COFs. Temperature‐dependent conductivity measurements reveal that the charge carriers in BUCT‐ COF‐1 exhibit the band‐like transport mechanism, which is entirely different from the hopping transport phenomena observed in common organic materials. The findings indicate that fully conjugated 3D COFs can achieve electron delocalization and charge‐transport pathways within the whole 3D skeleton, which may open up a new frontier in the design of organic semiconducting materials.
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