Deciphering Dynamic Self-Healing for Crystallinity Control in β-Ketoenamine-Linked Covalent Organic Frameworks.
Abstract
Covalent organic frameworks derived from triformylphloroglucinol (Tp-COFs) represent a prominent branch of COFs due to their high potential in separation, energy storage, and optoelectronics. However, the development of Tp-COFs is often hindered by limited crystallinity, resulting from the low reversibility of β-ketoenamine bond formation. In this study, we report an unprecedented dynamic self-healing mechanism during Tp-COF formation, arising from a reversible Michael-addition-elimination (MAE) process. Building on this insight, a modulator-mediated MAE pathway is further established for crystallinity control. As a representative example, Tp-COF-1 synthesized via this strategy (Tp-COF-1(H)) forms well-defined columnar crystals with domain sizes up to 20 µm × 2 µm, and exhibits significantly improved structural order, as evidenced by a sharper powder x-ray diffraction (PXRD) peak (full width at half maximum: 0.44° vs. 0.74°) and a higher specific surface area (1314 vs. 647 m2 g-1), compared to Tp-COF-1 synthesized by the conventional method (Tp-COF-1(O)). Moreover, optical pump-terahertz probe spectroscopy reveals a photoexcited charge-carrier mobility of 10.84 cm2 V-1 s-1 for Tp-COF-1(H), which is 1.77 times higher than that of Tp-COF-1(O). These findings identify dynamic self-healing process via MAE as a key mechanism for governing Tp-COF crystallization toward highly ordered Tp-COFs for optoelectronic applications.