Regulating Keto–Enol Tautomerism of β-Ketoenamine Covalent–Organic Frameworks for Photocatalytic Oxidative Coupling of Amines

Abstract

Covalent–organic frameworks (COFs), as promising metal-free porous catalysts, have become a hot research topic in the field of (photo)­catalysis. Herein, a series of β-ketoenamine COFs are synthesized using different amino and aldehyde monomers, and these COFs exhibit diverse characteristics in terms of crystallinity, chemical structure, microscopic morphology, and optoelectronic properties. TpBD-(CH3)2 synthesized from 2,4,6-triformylphloroglucinol and o-tolidine exhibits an extended π-conjugated structure and higher crystallinity as well as a more suitable redox potential, which greatly enhances the photocatalytic activity of benzylamine oxidation. Besides, the increased number of hydroxyl groups on the trialdehyde-based monomer contributes to more ketoamines in the TpTAB skeleton, which is favorable for photocatalysis. Meanwhile, β-ketoenamine COFs can rapidly increase their own temperature through internal structural evolution under light irradiation, thus boosting photocatalytic oxidative coupling of amines with high efficiency. This work could provide some guidance for the rational design of functional β-ketoenamine COFs for advanced photocatalytic organic transformations.

Designing Local Electron Delocalization in 2D Covalent Organic Frameworks for Enhanced Sunlight-Driven Photocatalytic Activity

“…A possible reaction pathway is proposed in Figure C based on the above results and literature reports . Under visible light irradiation, the electrons in the LUMO of TPBD- CN -COF are excited and migrate to the HOMO.…”

Ion-transporting channel-embedded MOF-in-COF structures as composite quasi-solid electrolytes with highly enhanced electrochemical properties

“…3b. 47,48 This structure is further conrmed in the C 1s XPS spectrum of MC which shows the presence of C]O and C-O bonds at 289.5 eV and 286.2 eV, respectively, as shown in Fig. S6.…”

Continuous Scavenging of Long-Lived Reactive Radicals for Enhancing the Photocatalytic Reduction Efficiency of Conjugated Polymers

“…Combining the band gaps from the DRS test, we obtained the valence and conduction band positions of the different polymers, as shown in Figure f. The band structures obtained through M-S and DRS testing show some discrepancies compared to those obtained from DFT simulations, which may be due to the gap between the inherent disordered structure of conjugated polymers and the limited structural units chosen for DFT simulation testing. − However, a consistent conclusion can be drawn that both DFT computational simulations and experimental tests indicate that the introduction of alkynyl groups can effectively reduce the band gap. Additionally, the conduction bands of all polymers are higher than the redox potential of Cr­(VI)/Cr­(III), which is −0.13 V vs NHE. , This suggests that all polymer photocatalysts have the ability to convert Cr­(VI) to Cr­(III).…”