A Crystalline Three-Dimensional Covalent Organic Framework with Flexible Building Blocks

Abstract

The construction of three-dimensional covalent organic frameworks (3D COFs) has proven to be very challenging, as their synthetic driving force mainly comes from the formation of covalent bonds. To facilitate the synthesis, rigid building blocks are always the first choice for designing 3D COFs. In principle, it should be very appealing to construct 3D COFs from flexible building blocks, but there are some obstacles blocking the development of such systems, especially for the designed synthesis and structure determination. Herein, we reported a novel highly crystalline 3D COF (FCOF-5) with flexible C–O single bonds in the building block backbone. By merging 17 continuous rotation electron diffraction data sets, we successfully determined the crystal structure of FCOF-5 to be a 6-fold interpenetrated pts topology. Interestingly, FCOF-5 is flexible and can undergo reversible expansion/contraction upon vapor adsorption/desorption, indicating a breathing motion. Moreover, a smart soft polymer composite film with FCOF-5 was fabricated, which can show a reversible vapor-triggered shape transformation. Therefore, 3D COFs constructed from flexible building blocks can exhibit interesting breathing behavior, and finally, a totally new type of soft porous crystals made of pure organic framework was announced.

Covalent organic frameworks: Design and applications in electrochemical energy storage devices

“…48,150,151 For instance, MD simulation can predict accurate COF structures whose simulated PXRD patterns can be analyzed in conjunction with experimentally observed patterns to investigate a particular stacking arrangement in COF systems. 65,130,[152][153][154][155] It has been well known that the stacking arrangement is a critical factor that can impact ion mobility and electronic conductivity in COFs. 46,118 However, it should be noted that the results obtained from computational modeling methods are often sensitive to the level of theory employed in characterizing the properties of COF.…”

Tunable Cage-Based Three-Dimensional Covalent Organic Frameworks

“…Due to the unique study field and limited research methods, very few flexible building blocks have been identified to date for constructing dynamic 3D COFs, such as macrocycle γ-cyclodextrin (γ-CD), 38 bicyclooxacalixarenes, 39 and so on. 40 Generally, these building blocks feature flexible C-O single bonds which provide more possibilities for structural diversity. Meanwhile, dynamic behaviors of these 3D COFs have been identified in response to external stimuli, such as solvent or vapor.…”

Ionic Covalent Organic Frameworks for Energy Devices

“…Porosity combined with their stable covalent bonds makes COFs ideal materials for ion conduction. [ 47–51 ] In addition, the variety of COF structures and their superior electrochemical stability has led COFs to become versatile platforms for an array of engineering applications. This is aided by the functionalizability of COF backbones, which can afford COF platforms for energy devices [ 52–58 ] and a diversity of other applications, such as molecular sorption and separation, [ 59–65 ] molecular sensing, [ 66,67 ] catalysis, [ 68–73 ] optoelectronics, [ 74–78 ] piezoelectrics, [ 79 ] and low‐ k dielectric materials [ 80,81 ]…”

“…Porosity combined with their stable covalent bonds makes COFs ideal materials for ion conduction. [47][48][49][50][51] In addition, the variety of COF structures and their superior electrochemical stability has led COFs to become versatile Covalent organic frameworks (COFs) are a class of porous crystalline materials whose facile preparation, functionality, and modularity have led to their becoming powerful platforms for the development of molecular devices in many fields of (bio)engineering, such as energy storage, environmental remediation, drug delivery, and catalysis. In particular, ionic COFs (iCOFs) are highly useful for constructing energy devices, as their ionic functional groups can transport ions efficiently, and the nonlabile and highly ordered all-covalent pore structures of their backbones provide ideal pathways for long-term ionic transport under harsh electrochemical conditions.…”