A New Squaraine‐Linked Triazinyl‐Based Covalent Organic Frameworks: Preparation, Characterization and Application for Sensitive and Selective Determination of Fe 3+ Cations

Ketazine-Linked Crystalline Porous Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a class of crystalline porous materials with well-defined π arrays and ordered channels, which can be predesigned with a topology diagram and prepared via a polycondensation reaction. Over the past decade, various types of π building units with different functional groups have been developed. Among them, aldehyde is one of the most widely used monomers that form COFs with azine, hydrazine, imine, squaranine, and C═C linkages. In contrast, its closest analogue, i.e., ketone, despite its broad structural diversity, has not yet been investigated for the design and synthesis of COFs. Herein we report the first examples of ketazine-linked COFs by developing ketones as monomers to enable polycondensation with hydrazine under solvothermal conditions. We observed that a careful screening of reaction conditions including solvent, catalyst, concentration, reaction temperature, and reaction time leads to the finding of optimal polymerization systems to produce highly crystalline and porous ketazine-linked COFs. Surprisingly, the ketazine linkage enables π conjugation between knot and linker sites and renders the resultant materials able to emit a strong blue fluorescence, highlighting the π electronic features of this new family of COFs. Our findings of ketones as monomers and ketazine as linkage bring unprecedented structures, functions, and applications to the field of COFs.

Interlayer Interactions and Macroscopic Property Calculations of Squaric-Acid-Linked Zwitterionic Covalent Organic Frameworks: Structures, Photocatalytic Carrier Transport, and a DFT Study

Squaric-acid-linked zwitterionic covalent organic frameworks (Z-COFs), assembled through interlayer interactions, are emerging as potential materials in the field of photocatalysis. However, the study of their interlayer interactions has been largely overlooked. To address this, this work systematically calculated interlayer interactions via density functional theory (DFT) and analyzed the differences in interlayer interactions of different structures of Z-COFs through interlayer slippage, planarity, and an independent gradient model based on the Hirshfeld partition (IGMH). Furthermore, it revealed the relationship between the interactions and the macroscopic photocatalytic carrier transport performance of the material. The results indicated that both preventing interlayer slippage and enhancing planarity can enhance the interlayer interactions of Z-COFs, thereby improving their macroscopic carrier transport performance in photocatalysis.

Recent Progress of Covalent Organic Frameworks Applied in Electrochemical Sensors

As an emerging porous crystalline organic material, the covalent organic frameworks (COFs) are given more and more attention in many fields, such as gas storage and separation, catalysis, energy storage and conversion, luminescent devices, drug delivery, pollutant adsorption and removal, analysis and detection due to their special advantages of high crystallinity, flexible designability, controllable porosities and topologies, intrinsic chemical and thermal stability. In recent years, the COFs are applied in analytical chemistry, for instance, chromatography, solid-phase microextraction, luminescent and colorimetric sensing, surface-enhanced Raman scattering and electroanalytical chemistry. The COFs decorated electrodes show high performance for detecting trace substances with remarkable selectivity and sensitivity, such as heavy metal ions, glucose, hydrogen peroxide, drugs, antibiotics, explosives, phenolic compounds, pesticides, disease metabolites and so on. This review mainly summarized the application of COF based electrochemical sensor according to different target analytes.

Highly stable β-ketoenamine-based covalent organic frameworks (COFs): synthesis and optoelectrical applications

Covalent organic frameworks (COFs) are one class of porous materials with permanent porosity and regular channels, and have a covalent bond structure. Due to their interesting characteristics, COFs have exhibited diverse potential applications in many fields. However, some applications require the frameworks to possess high structural stability, excellent crystallinity, and suitable pore size. COFs based on β-ketoenamine and imines are prepared through the irreversible enol-to-keto tautomerization. These materials have high crystallinity and exhibit high stability in boiling water, with strong resistance to acids and bases, resulting in various possible applications. In this review, we first summarize the preparation methods for COFs based on β-ketoenamine, in the form of powders, films and foams. Then, the effects of different synthetic methods on the crystallinity and pore structure of COFs based on β-ketoenamine are analyzed and compared. The relationship between structures and different applications including fluorescence sensors, energy storage, photocatalysis, electrocatalysis, batteries and proton conduction are carefully summarized. Finally, the potential applications, large-scale industrial preparation and challenges in the future are presented.

A novel 2D mesoporous phosphazene-anthraquinone-based covalent organic polymer: synthesis, characterization and supercapacitor applications

A novel phosphazene anthraquinone-based covalent organic polymer (HD-1) was successfully designed and synthesized through a simple polymerization reaction. The as-prepared material was used as an electrode active material for a supercapacitor.