Azobenzene Functionalized Organic Covalent Frameworks: Controlled Morphologies and Photo‐Regulated Adsorption

Abstract

Covalent organic frameworks (COFs) containing azobenzene building blocks carry great potential for use in intelligent storage, separation, chemical sensing, and catalysis due to their intriguing photo‐responsiveness. However, azobenzene units are often exploited as the linkers to form the framework of COFs, thereby restricting their molecular motion and photoisomerization. Herein, a simple yet robust template‐free solvothermal strategy is reported to yield azobenzene‐dangled COFs (Azo‐COFs) with their azobenzene moieties suspending within the pores. The crystallinity, specific surface area, and morphology of Azo‐COFs can be conveniently tailored by changing the ratio of amine to aldehyde monomers. Notably, the Azo‐COFs provide sufficient free space for the reversible trans‐to‐cis isomerization of the dangled azobenzene units inside the pores, thus reversibly regulating surface wettability of Azo‐COFs. The adsorption capacity of Azo‐COFs toward organic dye molecules is increased by 3.7‐fold when irradiated with ultraviolet light, which can be ascribed to the intelligent closing/opening of molecular gates rendered by photoisomerization of azobenzene moieties. As such, the ability to photoregulate the adsorption of Azo‐COFs highlights their significance in functioning as smart porous nanomaterials for applications in cargo release, molecular sieves, ion transport, energy conversion systems, and environmental remediation.

Ultrathin Polymer Nanotubes Assembled from Side-Chain Amphiphilic Alternating Azocopolymers for the Potential of Highly-Efficient and Photo-Controllable Dye Removal

“…1−3 To address this issue, an effective strategy was to develop desirable absorbents with high adsorption rates and excellent adsorption capacity, requiring unique structural merits of large specific surface areas and abundant functional groups. 4 Hence, numerous substances, including carbon, 5,6 zeolites, 7 metal−organic frameworks, 8 covalent organic frameworks, 9,10 polymer-based nanocomposites, 11−13 ultrathin organic nanomaterials (UTONMs), 14−16 etc., have been rationally designed and fabricated to remove organic pollutants from wastewater. Among them, synthetic UTONMs have emerged attractive attention due to their architectural versatility, facile synthesis, low density, and abundant functional groups on the surface.…”

“…Organic pollutants, such as highly water-soluble, nondegradable, potentially toxic, and carcinogenic organic dyes, are the primary contaminants in wastewater from industrial production and manufacturing, posing a serious threat to ecosystems and human health. − To address this issue, an effective strategy was to develop desirable absorbents with high adsorption rates and excellent adsorption capacity, requiring unique structural merits of large specific surface areas and abundant functional groups . Hence, numerous substances, including carbon, , zeolites, metal–organic frameworks, covalent organic frameworks, , polymer-based nanocomposites, − ultrathin organic nanomaterials (UTONMs), − etc., have been rationally designed and fabricated to remove organic pollutants from wastewater. Among them, synthetic UTONMs have emerged attractive attention due to their architectural versatility, facile synthesis, low density, and abundant functional groups on the surface. − The introduction of hollow nanostructures and a decrease in the dimension and size of UTONMs are necessary to increase the specific surface area, pollutant binding sites, and subsequent adsorption performance. , Therefore, the development of ultrathin organic nanotube-based absorbents with high absorption rates and controllable adsorption capacity is inevitable, which has rarely been studied so far.…”

Ratiometric Fluorescent Detection of Chromium(III) Based on One-Dimensional Imine-Linked Covalent Organic Framework

“…Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials, have attracted considerable attention in many fields due to its low density, , high stability, , high porosity, , and designable pore structure. − The ordered pore channels and abundant charge sites of COFs make them very attractive as host materials for identification and detection of guest ions. − Moreover, The π–π stacking of the pyrene layers and anthracene layers in the Z -direction will boost the conjugation of COFs, endowing COFs with good luminescence performance . Until now, for Cr 3+ detection, COF-based ratiometric fluorescence sensors have not been reported; therefore, it is of great significance to develop various ratiometric fluorescence COF sensors.…”