Synthesis of Vinylene-Linked Covalent Organic Frameworks by Monomer Self-Catalyzed Activation of Knoevenagel Condensation

Abstract

Reticular chemistry based on thermodynamically controlled linking modes and numerous organic building blocks has constituted versatile crystalline frameworks in molecular-level precision. However, vinylene-linked covalent organic frameworks (COFs) are still quite far from flexible tailoring in either their structures or topologies, due to the lack of monomers with sufficient activities. Herein, we establish a strategy to synthesize vinylene-linked COFs via Knoevenagel condensation between a tetratopic monomer 2,2′,6,6′-tetramethyl-4,4′-bipyridine (TMBP) and linear aromatic dialdehydes in a mixed solvent of benzoic anhydride and benzoic acid. Mechanistic investigation suggests that the condensation was promoted by a pyridine self-catalyzed benzoylation upon the cleavage of benzoic anhydride solvent molecules. The layered structures of the resultant COFs are highly crystallized into orthorhombic lattices with vertically aligned AA stacking modes, delivering high surface areas up to 1560 m 2 g −1 . The π-extended conjugated skeletons comprising para-bipyridyl units and vinylene linkages endow these COFs with substantial semiconducting properties, releasing visible-light-stimulated catalytic activity in water-splitting hydrogen evolution with a rate as high as 3230 μmol g −1 h −1 .

Design and Synthesis of a Zeolitic Organic Framework**

“…Covalent organic frameworks (COFs) [5, 6] are an emerging class of crystalline porous polymers that are assembled from organic building blocks linked by covalent bonds. Since the initiated work of Yaghi in 2005, these materials have attracted extensive attention in different fields, such as energy storage, gas separation, heterogeneous catalysis, optoelectronics, and many others [7–16] . Recently, developing three‐dimensional (3D) COF materials has been considered indispensable because of their promising advantages in interconnected pores and higher specific surface areas than two‐dimensional (2D) counterparts [17–19] .…”

Incorporating Conducting Polypyrrole into a Polyimide COF for Carbon‐Free Ultra‐High Energy Supercapacitor

“…In addition, the flakes exhibited ordered hexagonal pores under the HRTEM as expected (Figure S23, Supporting Information). [ 50,51 ]…”

“…In addition, the flakes exhibited ordered hexagonal pores under the HRTEM as expected (Figure S23, Supporting Information). [50,51] Distinct SAED patterns of COFs (at 5 nm −1 scale bar) showed the presence of diffraction of [00l] planes at a higher angle (Figure 2E-iii)). However, the lower angle reflections are merged in the smaller diameter range of the SAED, closer to the bright center of the direct TEM beam.…”

Integrating Light‐Harvesting Ruthenium(II)‐based Units into Three‐Dimensional Metal Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution

“…The higher performance of RuCOF-TPB as compared to the other two materials could be ascribed to the cumulative effect of its broader light absorption range (Figure 4a), more efficient photoinduced electron-hole separation (Figures 4c and S46), and higher hydrophilicity (Figure S47). Noteworthily, the HER activity of RuCOF-TPB is far superior to most of the reported MCOFs and COFs (Table S2), such as NiÀ BnÀ COF [25] (1805 μmol g À 1 h À 1 ), sp 2 c-COF [41] (1360 μmol g À 1 h À 1 ) and COF-DFB [42] (2120 μmol g À 1 h À 1 ). Moreover, the apparent quantum efficiency of RuCOF-TPB measuring at 420 nm was 6.95 %, which is also higher than most of the reported COF-based photocatalysts (Table S2).…”