A Fully Conjugated 3D Covalent Organic Framework Exhibiting Band-like Transport with Ultrahigh Electron Mobility

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.