Locking Covalent Organic Frameworks with Hydrogen Bonds: General and Remarkable Effects on Crystalline Structure, Physical Properties, and Photochemical Activity

Abstract

A series of two-dimensional covalent organic frameworks (2D COFs) locked with intralayer hydrogen-bonding (H-bonding) interactions were synthesized. The H-bonding interaction sites were located on the edge units of the imine-linked tetragonal porphyrin COFs, and the contents of the H-bonding sites in the COFs were synthetically tuned using a three-component condensation system. The intralayer H-bonding interactions suppress the torsion of the edge units and lock the tetragonal sheets in a planar conformation. This planarization enhances the interlayer interactions and triggers extended π-cloud delocalization over the 2D sheets. Upon AA stacking, the resulting COFs with layered 2D sheets amplify these effects and strongly affect the physical properties of the material, including improving their crystallinity, enhancing their porosity, increasing their light-harvesting capability, reducing their band gap, and enhancing their photocatalytic activity toward the generation of singlet oxygen. These remarkable effects on the structure and properties of the material were observed for both freebase and metalloporphyin COFs. These results imply that exploration of supramolecular ensembles would open a new approach to the structural and functional design of COFs.

From Discrete Molecular Cages to a Network of Cages Exhibiting Enhanced CO2 Adsorption Capacity

“…[12] It is interesting that addition of hydroxy groups does not lead to at otally different structure,w hich may allow for the introduction of some other functional groups without altering the [3+ +6] cage configuration. In the crystal stacking of NC1, neighboring cages adopt the columnar packing with ab ite angle of 608 8 ( Figure S16), which is analogous to the so-called window-towindow crystal stacking fashion [6] originated from the chiral interactions between two opposite enantiomers via the "mixand-match" strategy.T hus,i nterconnected one-dimensional (1D) tubular channel is generated running through the intrinsic cage voids,w hich is similar to that observed in the NDI-D [15] and racemic TCC1 cage (Figures S15, 16). [14] Tw odifferent types of imine units can be found in the molecular structure of NC1.…”

Covalent organic frameworks based on Schiff-base chemistry: synthesis, properties and potential applications

“…23,24 On the other hand, the use of an irreversible enol to-keto tautomerization following the Schiff-base reaction is also an effective strategy toward the enhancement of chemical stability of the crystalline framework. Thus, the chemical stability and crystallinity in 2D-COFs enhance by introducing -OH functionalities adjacent to the Schiffbase centres (CQN) to form an intramolecular O-HÁ Á ÁNQC hydrogen bond.…”

“…23,24 The H-bonding interactions also play an important role in the construction of the layered framework in 2D-COFs. Thus, stability, crystallinity and porosity can be tuned by using this modification.…”

Kovalente organische Netzwerke und Käfigverbindungen: Design und Anwendungen von polymeren und diskreten organischen Gerüsten

“…[198] Derartige Tandemansätze kçnnten in Zukunft die Bandbreite an zugänglichen COF-Vorstufen mit limitierten Lçslichkeiten und Stabilitäten erweitern. [199] Deutlich kürzere Reaktionszeiten bei tieferen Te mperaturen wurden in mikrowellenunterstützten [200][201][202] oder sonochemischen [203] Synthesen sowie organischen Te rracotta-Prozessen [204] erreicht. [199] Deutlich kürzere Reaktionszeiten bei tieferen Te mperaturen wurden in mikrowellenunterstützten [200][201][202] oder sonochemischen [203] Synthesen sowie organischen Te rracotta-Prozessen [204] erreicht.…”