Porous Organic Materials Research Articles

Spirobifluorene‐Based Porous Organic Salts: Their Porous Network Diversification and Construction of Chiral Helical Luminescent Structures

AbstractPorous organic salts (POSs) are organic porous materials assembled via charge‐assisted hydrogen bonds between strong acids and bases such as sulfonic acids and amines. To diversify the network topology of POSs and extend its functions, this study focused on using 4,4′,4′′,4′′′‐(9,9′‐spirobi[fluorene]‐2,2′,7,7′‐tetrayl)tetrabenzenesulfonic acid (spiroBPS), which is a tetrasulfonic acid comprising a square planar skeleton. The POS consisting of spiroBPS and triphenylmethylamine (TPMA) (spiroBPS/TPMA) was constructed from the two‐fold interpenetration of an orthogonal network with pts topology, which has not been reported in conventional POSs, owing to the shape of the spirobifluorene backbone. Furthermore, combining tris(4‐chlorophenyl)methylamine (TPMA‐Cl) and tris(4‐bromophenyl)methylamine (TPMA‐Br), which are bulkier than TPMA owing to the introduction of halogens at the p‐position of the phenyl groups with spiroBPS allows us to construct novel POSs (spiroBPS/TPMA‐Cl and spiroBPS/TPMA‐Br). These POSs were constructed from a chiral helical network with pth topology, which was induced by the steric hindrance between the halogens and the curved fluorene skeleton. Moreover, spiroBPS/TPMA‐Cl with pth topology exhibited circularly polarized luminescence (CPL) in the solid state, which has not been reported in hydrogen‐bonded organic frameworks (HOFs).

Spirobifluorene-Based Porous Organic Salts: Their Porous Network Diversification and Construction of Chiral Helical Luminescent Structures.

Porous organic salts (POSs) are organic porous materials assembled via charge-assisted hydrogen bonds between strong acids and bases such as sulfonic acids and amines. To diversify the network topology of POSs and extend its functions, this study focused on using 4,4',4'',4'''-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)tetrabenzenesulfonic acid (spiroBPS), which is a tetrasulfonic acid comprising a square planar skeleton. The POS consisting of spiroBPS and triphenylmethylamine (TPMA) (spiroBPS/TPMA) was constructed from the two-fold interpenetration of an orthogonal network with pts topology, which has not been reported in conventional POSs, owing to the shape of the spirobifluorene backbone. Furthermore, combining tris(4-chlorophenyl)methylamine (TPMA-Cl) and tris(4-bromophenyl)methylamine (TPMA-Br), which are bulkier than TPMA owing to the introduction of halogens at the p-position of the phenyl groups with spiroBPS allows us to construct novel POSs (spiroBPS/TPMA-Cl and spiroBPS/TPMA-Br). These POSs were constructed from a chiral helical network with pth topology, which was induced by the steric hindrance between the halogens and the curved fluorene skeleton. Moreover, spiroBPS/TPMA-Cl with pth topology exhibited circularly polarized luminescence (CPL) in the solid state, which has not been reported in hydrogen-bonded organic frameworks (HOFs).

Rational Synthesis of Functionalized Covalent Organic Frameworks via Four-Component Reaction.

The construction of function-oriented covalent organic frameworks (COFs) remains a challenge as it requires simultaneous consideration of diversified structures, robust linkage, and tailorable functionalities. Herein, we report the rational synthesis of functionalized COFs via a four-component reaction strategy. Through the four-component Debus-Radziszewski reaction, 11 N-substituted imidazole-based COFs with diversified structures were facilely constructed from readily available building blocks. By forming the N-substituted imidazole linkage, these synthesized COFs displayed ultrastability toward strong acids and base. Moreover, the four components reaction allows the rational synthesis of COFs with tailorable functionalities. As an example, the phosphonate-functionalized COF (LZU-530) was rationally constructed for the efficient adsorption of uranium(VI). The uranium(VI) uptake of LZU-530 reaches up to 95 mg·g-1 in 2 M HNO3, which is the highest uptake of the existing organic porous materials under such harsh conditions. Our results highlight the use of multicomponent reaction for the rational synthesis of robust and functionalized COFs toward targeted applications.

A Systematic Review of MOF, COF, and Their Hybrid‐Based Composite Membranes for Gas Separation

AbstractMembrane–based gas separation has become an important research field for sustainable energy and environmental applications. Gas separation is one of the key steps in refineries and other gas‐related industries. Over the last two decades, the research on extended porous organic and inorganic materials such as zeolites, metal–organic frameworks (MOFs), covalent–organic frameworks (COFs), and their hybrids has increased continuously. These materials have garnered significant interest due to their structural flexibility and pronounced porosity, which offer excellent potential for gas adsorption and separation processes in industrial settings. As such, this review has aimed to provide an in‐depth analysis of the recent developments in MOFs, COFs, and MOF–COF hybrid‐based membranes for gas separation, highlighting their potential for practical industrial applications. It also offers a comprehensive understanding of some of the most critical and advanced materials used in gas separation compared to common polymers. In addition, membranes' concepts, efficiency, and cost‐effectiveness are discussed in detail.

A New Porphyrin-based Covalent Organic Framework with High Iodine Capture Capacity and I-doping Enhanced Conductivity.

Covalent organic frameworks (COFs) are porous organic materials with well-defined and uniform structure. The material is an excellent candidate as a solid adsorbent for iodine adsorption. In the present study, we report the synthesis of COF with porphyrin moiety, TF-TA-COF, by solvothermal reaction, which was characterized by XRD, solid-state 13 C NMR, IR, TGA, and nitrogen adsorption-desorption analysis. TF-TA-COF showed a high specific surface area of 443 m2 g-1 , and exhibited good adsorption performance for iodine vapor, with an adsorption capacity of 2.74 g g-1 . XPS and Raman spectrum indicated that a hybrid of physisorption and chemisorption took place between host COF and iodine molecules. The electric properties of iodine-loaded TF-TA-COF were also studied. After doped with iodine, the conductivity of the material increased by more than 5 orders of magnitude. The photoconductivity of I2 -doped COF was also studied and TF-TA-COF showed doping-enhanced photocurrent generation.

Atomic observation and structural evolution of covalent organic framework rotamers

Dynamic 3D covalent organic frameworks (COFs) have shown concerted structural transformation and adaptive gas adsorption due to the conformational diversity of organic linkers. However, the isolation and observation of COF rotamers constitute undergoing challenges due to their comparable free energy and subtle rotational energy barrier. Here, we report the atomic-level observation and structural evolution of COF rotamers by cryo-3D electron diffraction and synchrotron powder X-ray diffraction. Specifically, we optimize the crystallinity and morphology of COF-320 to manifest its coherent dynamic responses upon adaptive inclusion of guest molecules. We observe a significant crystal expansion of 29 vol% upon hydration and a giant swelling with volume change up to 78 vol% upon solvation. We record the structural evolution from a non-porous contracted phase to two narrow-pore intermediate phases and the fully opened expanded phase using n-butane as a stabilizing probe at ambient conditions. We uncover the rotational freedom of biphenylene giving rise to significant conformational changes on the diimine motifs from synclinal to syn-periplanar and anticlinal rotamers. We illustrate the 10-fold increment of pore volumes and 100% enhancement of methane uptake capacity of COF-320 at 100 bar and 298 K. The present findings shed light on the design of smarter organic porous materials to maximize host-guest interaction and boost gas uptake capacity through progressive structural transformation.

Chiral aggregates of rod-coil molecules inside nanopores as efficient nanoreactors for asymmetric synthesis.

An important subject of porous organic materials is their capacity to access enantioselectivity due to their high surface area, controllable pore size, and ease of functionalization. However, recyclability of enantio-separation is a challenge, mainly due to the complex procedures of recovery and refreshing from enantiomers. For the first time, we combined nanochannel technology and supramolecular chiral assembly to achieve efficient enantioselectivity. Fine-designed amphiphilic chiral rod-coil molecules 1-3 were immobilized to SBA-15 pore walls to form SA-M1-3 (abbreviation for amino-functionalized SBA-15 connected to molecules 1-3), which commenced chiral aggregation inside the channels. The experimental results indicated that the strong π-π stacking interaction between the rigid terphenyl groups, as well as hydrophilic-hydrophobic interaction of the amphiphiles, assisted in chiral arrangement in aqueous solution, and was accompanied by amplification of chirality. As a result, porous chiral channels exhibiting enhanced efficiency in asymmetric synthesis were manufactured, where enantioselectivity can be controlled by the initial structural design of amphiphiles that induce chiral aggregation behaviors. The chiral centers of SA-M1 and SA-M2 are located on hydrophobic and hydrophilic coils, respectively, while SA-M3 possesses both chiral coils. The SA-M materials proceeded with chiral aggregation and behaved efficiently for enantioselectivity. SA-M3, which contained the most chiral centers, showed the most optimal enantioselectivity with an enantiomeric excess (ee) value up to 71.75%, which occurred because of the strongly driven chiral aggregation of the hydrophobic and hydrophilic chiral coils. The covalent hybrid structures of the SA-M materials can be easily refreshed simply through washing, and exhibited excellent recyclability with negligible loss of efficiency. Therefore, the SA-M materials have the ability to provide sustainable and reliable application value for enantiomer separation.

A sequential flow process of CO2 capture and conversion using cost-effective porous organic polymers

A sequential flow process utilizing cost-effective porous organic materials to capture CO2 and directly convert it into fine chemicals has been achieved, which could improve the practical applicability of CO2 capture and utilization technologies.

Crystalline porous organic salts.

Crystalline porous organic salts (CPOSs), formed by the self-assembly of organic acids and organic bases through ionic bonding, possess definite structures and permanent porosity and have rapidly emerged as an important class of porous organic materials in recent years. By rationally designing and controlling tectons, acidity/basicity (pKa), and topology, stable CPOSs with permanent porosity can be efficiently constructed. The characteristics of ionic bonds, charge-separated highly polar nano-confined channels, and permanent porosity endow CPOSs with unique physicochemical properties, offering extensive research opportunities for exploring their functionalities and application scenarios. In this review, we systematically summarize the latest progress in CPOS research, describe the synthetic strategies for synthesizing CPOSs, delineate their structural characteristics, and highlight the differences between CPOSs and hydrogen-bonded organic frameworks (HOFs). Furthermore, we provide an overview of the potential applications of CPOSs in areas such as negative linear compression (NLC), proton conduction, rapid transport of CO2, selective and rapid transport of K+ ions, atmospheric water harvesting (AWH), gas sorption, molecular rotors, fluorescence modulation, room-temperature phosphorescence (RTP) and catalysis. Finally, the challenges and future perspectives of CPOSs are presented.

COFs as porous organic materials for the separation and purification of ethylene from C2 hydrocarbons.

With rapid societal development, there has been a significant increase in the demand for chemicals. Ethylene, as the most widely used basic chemical, is now subject to increasingly stringent quality and purity standards. The separation and purification of ethylene from C2 hydrocarbons via covalent organic frameworks (COFs) are a fascinating and challenging area of research. Compared with conventional separation techniques, COFs have demonstrated the capacity to efficiently separate and purify analogues while simultaneously reducing energy consumption. As a result, it is urgent to conduct a study on COF applications in separating and purifying ethylene from C2 hydrocarbons to foster greater advancement in this field. This review provides an overview of research on ethylene separation, discusses the results and effective strategies reported for the use of COFs in ethylene separation to date, and presents challenges encountered in the current development process. The aim of this review is to inspire the design of COFs for ethylene separation and facilitate further development in this emerging field.

Network topology diversification of porous organic salts.

Hydrogen-bonded organic frameworks (HOFs) are porous organic materials constructed via hydrogen bonds. HOFs have solubility in specific high-polar organic solvents. Therefore, HOFs can be returned to their components and can be reconstructed, which indicates their high recyclability. Network topologies, which are the frameworks of porous structures, control the pore sizes and shapes of HOFs. Therefore, they strongly affect the functions of porous materials. However, hydrogen bonds are usually weak interactions, and the design of the intended network topology in HOFs from their components has been challenging. Porous organic salts (POSs) are an important class of HOFs, are hierarchically constructed via strong charge-assisted hydrogen bonds between sulfonic acids and amines, and therefore are expected to have high designability of the porous structure. However, the network topology of POSs has been limited to only dia-topology. Here, we combined tetrasulfonic acid with the adamantane core (4,4',4'',4'''-(adamantane-1,3,5,7-tetrayl)tetrabenzenesulfonic acid; AdPS) and triphenylmethylamines with modified substituents in para-positions of benzene rings (TPMA-X, X = F, methyl (Me), Cl, Br, I). We changed the steric hindrance between the adamantane and substituents (X) in TPMA-X and obtained not only the common dia-topology for POSs but also rare sod-topology, and lon- and uni-topologies that are formed for the first time in HOFs. Changing template molecules under preparation helped in successfully isolating the porous structures of AdPS/TPMA-Me with dia-, lon-, and sod-topologies which exhibited different gas adsorption properties. Therefore, for the first time, we demonstrated that the steric design of HOF components facilitated the formation, diversification, and control of the network topologies and functions of HOFs.

Unraveling the orientation of an enzyme adsorbed onto a metal-organic framework.

Bio-conversion of lignocellulosic biomass to bioethanol fuel is a highly desirable yet challenging objective because of the low catalytic activity and high cost of β-glucosidase (BGL). Recently, ZIF-8, an emerging organic porous material, has been proposed as a promising candidate for enzyme immobilization to improve associated activity and stability. However, the underlying interaction mechanism of binding BGL on the ZIF-8 surface is yet to be clarified. Here, the adsorption of BGL onto ZIF-8 is explored for the first time by molecular dynamics simulations. The results show that BGL adsorbs on the ZIF-8 surface with a "back-on" orientation. The adsorption free energy analysis shows that the adsorption process is enthalpy driven. In addition, the electrostatic interaction between negatively charged residues and Zn2+ on the surface of ZIF-8 is found to play a decisive role in surface binding, which accounts for 98% of the total interaction energy. The secondary structure of BGL is not affected despite the strong adsorption, suggesting the good biocompatibility of ZIF-8. This study not only provides a reliable theoretical insight into understanding the interaction mechanism between BGL and ZIF-8, but also helps the rational design of ZIF-8-based materials for bio-related applications.

Metal-Free Heterogeneous Asymmetric Hydrogenation of Olefins Promoted by Chiral Frustrated Lewis Pair Framework.

The development of metal-free and recyclable catalysts for significant yet challenging transformations of naturally abundant feedstocks has long been sought after. In this work, we contribute a general strategy of combining the rationally designed crystalline covalent organic framework (COF) with a newly developed chiral frustrated Lewis pair (CFLP) to afford chiral frustrated Lewis pair framework (CFLPF), which can efficiently promote the asymmetric olefin hydrogenation in a heterogeneous manner, outperforming the homogeneous CFLP counterpart. Notably, the metal-free CFLPF exhibits superior activity/enantioselectivity in addition to excellent stability/recyclability. A series of in situ spectroscopic studies, kinetic isotope effect measurements, and density-functional theory computational calculations were also performed to gain an insightful understanding of the superior asymmetric hydrogenation catalysis performances of CFLPF. Our work not only increases the versatility of catalysts for asymmetric catalysis but also broadens the reactivity of porous organic materials with the addition of frustrated Lewis pair (FLP) chemistry, thereby suggesting a new approach for practical and substantial transformations through the advancement of novel catalysts from both concept and design perspectives.

Dual functional porous organic polymer: Reversible iodine capture and selective sensing of picric acid

The development of porous organic materials for removing radiotoxic iodine from nuclear plant waste is significantly relevant to environmental remediation as well as the detection of trace amounts of nitroexplosive picric acid for environmental safety is challenging. To achieve reversible iodine adsorption by the porous material, we have synthesized a highly stable porous organic polymer POF-1 by Schiff base condensation of tris(4-aminophenyl)methane and 2,2′-bithiophene-5,5′-dicarbaxaldehyde under microwave irradiation. POF-1 showed high affinity towards iodine adsorption due to electron-rich sulfur and nitrogen atoms in the porous structure which interact with iodine and form polyiodide ions by electrostatic interactions. POF-1 showed a remarkable iodine uptake capacity of 4.25 g g−1 in the vapor phase and could efficiently remove iodine from an iodine-cyclohexane solution with an adsorption efficiency of 141.0 mg/L. The iodine adsorption follows Langmuir's isothermal model i.e. monolayer adsorption and Pseudo second-order kinetics. POF-1 exhibited good recyclability towards reversible iodine capture even after five cycles. Furthermore, the luminescence characteristic of POF-1 has been employed for the selective detection of picric acid with high sensitivity with a detection limit of 8 μM among a range of nitroaromatic. The Fluorescence quenching mechanism is mainly attributed to photo-induced electron transfer and the inner filter effect.

Covalent Organic Frameworks (COFs): Characteristics and Applications for Lithium-Ion Batteries (LIBs) and Sodium Ion Batteries (SIBs)

Covalent organic frameworks (COFs) belong to a family of porous organic materials that form 2D or 3D tuned structures via a covalent bond formation between organic blocks. COFs exhibit a remarkable array of characteristics that make them highly promising materials for various applications. COFs are characterized by their chemical and physical stability, their highly porous structure, and their easy structural tunability. They emerged as promising candidates for electrode materials in advanced energy storage devices such as sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). COFs can be precisely customized for each application via pore engineering and framework functionalization as well as the pre- and post-synthesis. Research has been conducted to examine the effect of various functional groups, active redox sites, pore size, and interlayer distances on the performance of COFs as electrode materials. Herein, this review reports the most recent advances in using COFs as electrode materials in both LIBs and SIBs. It also discusses the synthesis of COFs, structural engineering, and pore engineering. The main advantages and challenges that arise with the application of COFs in rechargeable batteries are presented. This review concluded that COFs do have the potential as anode materials in both LIBs and SIBs by virtue of their crystalline structure and high porosity that enable efficient ion diffusion and storage. COFs provided enhanced battery electrochemical performance, improved energy density, and prolonged cycle life.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

AbstractNanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function‐oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF‐based anticancer nanomedicines and bringing COFs closer to clinical trials.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy.

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Engineering Photocatalytic Porous Organic Materials for Directing Redox versus Energy Transfer Processes

Two organic materials containing phenanthroline and triazine fragments, but connected in different ways, are presented. The imine‐based material Phen–Tz–covalent organic framework (COF) preferentially shows photocatalytic activity through an energy transfer pathway as observed for olefin photoisomerization. However, an analogous covalent triazine framework (Phen–CTF) behaves as a powerful photoredox catalyst able to activate CX (X=Br, Cl) bonds. The analysis of this phenomenon by means of theoretical calculations enables the rationalization of the different photocatalytic behavior observed. Phen–CTF behaves as a donor–acceptor material resulting in efficient charge separation upon excitation, while the imine groups present in Phen–Tz–COF hamper charge separation contributing to the rapid recombination between electrons and holes. This justifies a better activation via electron transfer in Phen–CTF and via energy transfer in Phen–Tz–COF.

Azide Thermolysis Frameworks: Self‐inflating, Porous, and Lightweight Materials

AbstractPorous organic materials have received increasing attention due to their potential applications, such as gas storage, gas separation, and catalysis. In this work, we present a series of aromatic, polyazide‐containing building blocks that enable the formation of a new class of amorphous porous organic materials. The azide precursors are obtained in moderate to good yields following an easy synthesis procedure. By thermal decomposition, self‐inflating porous structures named Azide Thermolysis Frameworks (ATFs) can be obtained. Modified thermogravimetric analysis is used to determine the onset temperature at which the azides decompose and the frameworks are formed. The frameworks are further investigated via infrared (IR) spectroscopy, elemental analysis, scanning electron microscopy (SEM), and gas adsorption measurements. Specific surface areas and pore sizes are determined by nitrogen adsorption measurements at 77 K using the Brunauer–Emmett–Teller method (BET) to give surface areas of up to 677 m2/g for the ATF resulting from the thermolysis of TPB‐Azide at 450 °C, which can compete with early Covalent Organic Frameworks (COFs). The specific surface area can be tuned by varying the thermolysis temperature.

Chemical conversion of imine- into quinoline-linked covalent organic frameworks for photocatalytic oxidation

Post-synthetic modification is an important strategy for improving and enhancing the properties and functions of covalent organic frameworks (COFs). Two imine-linked COFs are converted into the quinolone-linked COFs by converting the dynamic imine linkages in the COFs into more robust quinolone ring via aza-Diels-Alder cycloaddition reaction. The prepared quinolone-linked COFs not only maintain good crystallinity and porosity, but also possess expanded conjugate planes, enhanced light absorption and excellent stability. The quinolone-linked COFs present remarkable performance of photocatalytic oxidation reactions, including oxidation of phenylboric acids, coupling of benzylamine, and oxidation of thioethers. This work is helpful for preparing organic porous photocatalytic materials with high performance and long life.