Porous Organic Cages Research Articles

Transition Metal Nanoparticles‐Catalyzed Organic Reactions within Porous Organic Cages

AbstractTransition metal catalysis has played an important role in modern organic chemistry. In order to develop highly efficient and sustainable methodologies, considerable efforts have been devoted to combining the benefits of homogeneous catalysis and heterogeneous catalysis. Porous organic cages (POCs) are a relatively new type of discrete molecules with permanent cavities and good solubilities. These intrinsic properties make POCs expedient catalyst support for the homogenization of heterogeneous transition metal nanoparticles (MNPs). This review mainly focuses on the recent progress of MNPs‐catalyzed reductions and coupling reactions within POCs. In most cases, the MNPs@POC complexes have exhibited outstanding reactivity, dispersibility, stability, and reusability. These pioneering contributions have enriched the methodology toolbox for advanced organic synthesis.

Construction of Porphyrin Porous Organic Cage as a Support for Single Cobalt Atoms for Photocatalytic Oxidation in Visible Light

Construction of Porphyrin Porous Organic Cage as a Support for Single Cobalt Atoms for Photocatalytic Oxidation in Visible Light

Cover Feature: Sulfur Dioxide Capture in Metal‐Organic Frameworks, Metal‐Organic Cages, and Porous Organic Cages (ChemPlusChem 6/2022)

The cover feature image illustrates sulphur dioxide adsorption on three types of porous material: metal organic frameworks (MOFs), metal organic cages (MOCs), and porous organic cages (POCs), represented by sky lanterns. Each of the materials has advantages and disadvantages as SO2 adsorbents, which are discussed in this Review article, but without doubt all of them are needed as part of the global effort to mitigate the release of this polluting gas. Cover design by Alfredo López-Olvera and Eva Martínez-Ahumada. More information can be found in the Review by E. Martínez-Ahumada, I. A. Ibarra and co-workers.

Porous Organic Cages CC3 and CC2 as Adsorbents for the Separation of Carbon Dioxide from Nitrogen and Hydrogen

Porous Organic Cages CC3 and CC2 as Adsorbents for the Separation of Carbon Dioxide from Nitrogen and Hydrogen

Room temperature all-solid-state lithium batteries based on a soluble organic cage ionic conductor

All solid-state lithium batteries (SSLBs) are poised to have higher energy density and better safety than current liquid-based Li-ion batteries, but a central requirement is effective ionic conduction pathways throughout the entire cell. Here we develop a catholyte based on an emerging class of porous materials, porous organic cages (POCs). A key feature of these Li+ conducting POCs is their solution-processibility. They can be dissolved in a cathode slurry, which allows the fabrication of solid-state cathodes using the conventional slurry coating method. These Li+ conducting cages recrystallize and grow on the surface of the cathode particles during the coating process and are therefore dispersed uniformly in the slurry-coated cathodes to form a highly effective ion-conducting network. This catholyte is shown to be compatible with cathode active materials such as LiFePO4, LiCoO2 and LiNi0.5Co0.2Mn0.3O2, and results in SSLBs with decent electrochemical performance at room temperature.

Self-assembled artificial enzyme from hybridized porous organic cages and iron oxide nanocrystals

HypothesisAlthough it is well-accepted that iron oxide nanoparticles are considered as artificial enzymes when their surface is hydrophilic, the enzyme-like properties of iron oxide nanoparticles with hydrophobic surface coating is unexplored. This work demonstrates that hydrophobic iron oxide nanocrystals coated with a layer of oleic acid could serve as artificial enzymes when their surface is covered by a layer of ionic surfactant. Furthermore, the co-assembly of iron oxide nanocrystals and porous organic cages could modulate their enzyme-like activities. ExperimentsCo-assembly of iron oxide (Fe3O4) nanocrystals with different size and porous organic cages (POCs) was performed by an emulsion-confined strategy to achieve hybridized Fe3O4/POCs co-assemblies. The peroxidase-mimic activity of these co-assemblies were assessed in the presence of 3, 3′, 5, 5′-Tetramethylbenzidine (TMB) and hydrogen peroxide. Finally, these co-assemblies were applied as sensors to detect glucose and hydrogen peroxide. FindingsCo-assembly of Fe3O4 nanocrystals and POCs resulted in the self-assembly of Fe3O4 nanoparticles into two-dimensional nanoparticle superlattices on the eight (111) facets of the octahedral POCs colloidal crystals. The unique oil-in-water (O/W) emulsion confined assembly method switches the Fe3O4 nanoparticles and POC crystals from hydrophobic to hydrophilic because of the strong hydrophobic interactions. Importantly, these co-assemblies dispersed in water showed strong peroxidase-mimic activity in water despite that their surface is covered by a bilayer of aliphatic chains. Furthermore, the intrinsic enzymatic activity of the co-assemblies is highly dependent on the size of the nanocrystals, and a higher catalytic activity is achieved from a larger sized Fe3O4 nanocrystal.

Boosting the Productivity of Electrochemical CO2 Reduction to Multi-Carbon Products by Enhancing CO2 Diffusion through a Porous Organic Cage.

Electroreduction of CO2 into valuable fuels and feedstocks offers a promising way for CO2 utilization. However, the commercialization is limited by the low productivity. Here, we report a strategy to enhance the productivity of CO2 electroreduction by improving diffusion of CO2 to the surface of catalysts using porous organic cages (POCs) as an additive. It was noted that the Faradaic efficiency (FE) of C2+ products could reach 76.1 % with a current density of 1.7 A cm-2 when Cu-nanorod(nr)/CC3 (one of the POCs) was used, which were much higher than that using Cu-nr. Detailed studies demonstrated that the hydrophobic pores of CC3 can adsorb a large amount of CO2 for the reaction, and the diffusion of CO2 in the CC3 to the nanocatalyst surface is easier than that in the liquid electrolyte. Thus, more CO2 molecules make contact with the nanocatalysts in the presence of CC3, enhancing CO2 reduction and inhibiting generation of H2 .

Boosting the Productivity of Electrochemical CO2Reduction to Multi‐Carbon Products by Enhancing CO2Diffusion through a Porous Organic Cage

AbstractElectroreduction of CO2into valuable fuels and feedstocks offers a promising way for CO2utilization. However, the commercialization is limited by the low productivity. Here, we report a strategy to enhance the productivity of CO2electroreduction by improving diffusion of CO2to the surface of catalysts using porous organic cages (POCs) as an additive. It was noted that the Faradaic efficiency (FE) of C2+ products could reach 76.1 % with a current density of 1.7 A cm−2when Cu‐nanorod(nr)/CC3 (one of the POCs) was used, which were much higher than that using Cu‐nr. Detailed studies demonstrated that the hydrophobic pores of CC3 can adsorb a large amount of CO2for the reaction, and the diffusion of CO2in the CC3 to the nanocatalyst surface is easier than that in the liquid electrolyte. Thus, more CO2molecules make contact with the nanocatalysts in the presence of CC3, enhancing CO2reduction and inhibiting generation of H2.

N-heterocyclic carbene-stabilized metal nanoparticles within porous organic cages for catalytic application.

Tuning the surface-embellishing ligands of metal nanoparticles (NPs) is a powerful strategy to modulate their morphology and surface electronic and functional features, impacting their catalytic activity and selectivity. In this work, we report the design and synthesis of a polytriazolium organic cage PIC-T, capable of stabilizing PdNPs within its discrete cavity. The obtained material (denoted Pd@PCC-T) is highly durable and monodispersed with narrow particle-size distribution of 2.06 ± 0.02 nm, exhibiting excellent catalytic performance and recyclability in the Sonogashira coupling and tandem reaction to synthesize benzofuran derivatives. Further investigation indicates that the modulation of N-heterocyclic carbene sites embedded in the organic cage has an impact on NPs’ catalytic efficiency, thus providing a novel methodology to design superior NP catalysts.

Preparation and application of porous organic cage capillary electrochromatographic chiral column

多孔有机笼(POCs)是一种新型的具有稳定有序三维空腔结构的多孔材料。通过2-羟基-1,3,5-均苯三甲醛与1R,2R-1,2-二苯基乙二胺发生席夫碱的缩合反应,合成了一种具有羟基功能基团的单一手性POCs材料;将其均匀涂敷在毛细管壁上制成色谱柱,利用电色谱柱成功拆分了二氢黄酮、吡喹酮、萘普生和3,5-二硝基-N-(1-苯乙基)苯甲酰胺4种手性化合物。探究了分离电压、缓冲溶液浓度及其pH值等因素对手性拆分的影响,获得了4种手性物质在POCs色谱柱上的最佳拆分条件。实验研究表明,二氢黄酮、吡喹酮、萘普生和3,5-二硝基-N-(1-苯乙基)苯甲酰胺获得优化分离效果所需的工作电压分别为13、14、14和12 kV;二氢黄酮适宜Tris-H3PO4缓冲溶液浓度为0.075 mol/L,吡喹酮、萘普生和3,5-二硝基-N-(1-苯乙基)苯甲酰胺适宜Tris-H3PO4缓冲溶液浓度为0.100 mol/L; 4种手性物质得到最佳分离效果时的pH值均为3.51。二氢黄酮、吡喹酮、萘普生和3,5-二硝基-N-(1-苯乙基)苯甲酰胺均达到基线分离,分离度分别为2.99、2.10、2.58和3.59。该POCs色谱柱还成功拆分了o,m,p-碘苯胺、o,m,p-硝基苯胺两种位置异构体。该研究表明POCs手性电色谱柱具有良好的手性识别能力,是一种优秀的手性分离材料,具有很大的电色谱手性分离应用前景。

Preparation of Novel Chiral Stationary Phases Based on the Chiral Porous Organic Cage by Thiol-ene Click Chemistry for Enantioseparation in HPLC.

Porous organic cages (POCs) are an emerging class of porous materials that have aroused considerable research interest because of their unique characteristics, including good solubility and a well-defined intrinsic cavity. However, there have so far been no reports of chiral POCs as chiral stationary phases (CSPs) for enantioseparation by high-performance liquid chromatography (HPLC). Herein, we report the first immobilization of a chiral POC, NC1-R, on thiol-functionalized silica using a mild thiol-ene click reaction to prepare novel CSPs for HPLC. Two CSPs (CSP-1 and CSP-2) with different spacers have been prepared. CSP-1, with a cationic imidazolium spacer, exhibited excellent enantioselectivity for the resolution of various racemates. Twenty-three and 12 racemic compounds or chiral drugs were well enantioseparated on the CSP-1-packed column under normal-phase and reversed-phase conditions, respectively, including alcohols, diols, esters, ethers, ketones, epoxides, organic acids, and amines. In contrast, chiral resolution using CSP-2 (without a cationic imidazolium spacer)-packed column B was inferior to that of column A, demonstrating the important role of the cationic imidazolium spacer for chiral separation. The chiral separation capability of column A was also compared with that of two most popular commercial chiral columns, Chiralpak AD-H and Chiralcel OD-H, which exhibits good chiral recognition complementarity with the two commercial chiral columns. In addition, five positional isomers dinitrobenzene, nitroaniline, chloroaniline, bromoaniline, and iodoaniline were also well separated on column A. The effects of temperature, mobile phase composition, and injected analyte mass for separation on column A were investigated. Column A also showed good stability and reproducibility after repeated injections. This work demonstrates that chiral POCs are promising chiral materials for HPLC enantioseparation.

Recent advances in adsorptive separation of ethane and ethylene by C2H6-selective MOFs and other adsorbents

• The recent developments of C 2 H 6 -selective adsorbents are overviewed. • The method for boosting adsorption uptake, selectivity and stability is discussed. • The mechanism underlying the preferential adsorption of C 2 H 6 over C 2 H 4 is briefed. • Balancing the trade-off between adsorption uptake and selectivity is challenging. • Lowering cost and enhancing stability of MOF are future research directions. C 2 H 4 is the most important and demanded chemical raw materials. Separating C 2 H 6 from C 2 H 4 using C 2 H 6 -trapping adsorbents to lower the energy consumption in the petrochemical industry is important but challenging. This review summarizes the research progresses on the development of C 2 H 6 -selective metal–organic frameworks (MOFs), covalent-organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic cages (POCs), carbon-based materials, and zeolites for C 2 H 6 /C 2 H 4 separation. The C 2 H 6 uptakes, C 2 H 6 /C 2 H 4 selectivities, stability, cost, scale-up synthesis, regeneration performance and shaping of C 2 H 6 -selective MOFs are overviewed. The strategies for enhancing C 2 H 6 uptakes, C 2 H 6 /C 2 H 4 selectivities and moisture stability on MOFs are summarized. The mechanism underlying the preferential adsorption of C 2 H 6 over C 2 H 4 on different adsorbents is also highlighted. Additionally, challenges and future developments of various C 2 H 6 -selective adsorbents are discussed.

Mixed‐matrix gas separation membranes for sustainable future: A mini review

AbstractMixed‐matrix membranes (MMMs), merging the advantages of polymers and inorganic fillers, has become a preferable choice as future gas separation membrane. Owing to hierarchical structures, MMMs are suitable for high‐performance gas separation capability. Research on extended porous organic/inorganic materials also known as fillers of intrinsic nanopores (FINS) such as porous organic frameworks (POFs), Zeolites, metal–organic frameworks (MOFs), porous organic cages (POCs) and analogous metal–organic polyhedral (MOPs) have bloomed over the last two decades. MOFs and POFs have been proposed as good adsorbent and promising filler components for industrial gas separations, due to their prominent porosity and structural flexibility and also for MMMs with good performance in terms of permeance and selectivity. They are compatible for providing additional molecular transport channels as well as having good size‐sieving property. This review briefly outlines the innovative trends in MMMs, highlighted with different porous fillers as well as suitable polymers followed by their synthesis and their suitable application in gas separations. Finally, a state of art and challenges in the direction of actual application of MMMs in different industries are outlined in terms of inter relation and regarding the future direction and potential growth opportunities of MMMs an elaborate discussion is provided.

Design Elements for Enhanced Hydrogen Isotope Separations in Barely Porous Organic Cages.

Barely porous organic cages (POCs) successfully separate hydrogen isotopes (H2/D2) at temperatures below 100 K. Identifying the mechanisms that control the separation process is key to the design of next-generation hydrogen separation materials. Here, ab initio molecular dynamics (AIMD) simulations are used to elucidate the mechanisms that control D2 and H2 separation in barely POCs with varying functionalization. The temperature and pore size dependence were identified, including the selective capture of D2 in three different CC3 structures (RCC3, CC3-S, and 6ET-RCC3). The temperature versus capture trend was reversed for the 6ET-RCC3 structure, identifying that the D2 and H2 escape mechanisms are unique in highly functionalized systems. Analysis of calculated isotope velocities identified effective pore sizes that extend beyond the pore opening distances, resulting in increased capture in minimally functionalized CC3-S and RCC3. In a highly functionalized POC, 6ET-RCC3, higher velocities of the H isotopes were calculated moving through the restricted pore compared to the rest of the system, identifying a unique molecular behavior in the barely nanoporous pore openings. By using AIMD, mechanisms of H2 and D2 separation were identified, allowing for the targeted design of future novel materials for hydrogen isotope separation.

Sulfur Dioxide Capture in Metal-Organic Frameworks, Metal-Organic Cages, and Porous Organic Cages.

Capture, storage and subsequent controlled release or transformation of sulfur dioxide (SO2 ) in mild conditions is still a challenge in the material science field. Recent advances in the use of porous materials have demonstrated good SO2 capture, particularly in metal-organic frameworks (MOFs), metal-organic cages (MOCs), and porous organic cages (POCs). The striking feature of these porous materials is the high SO2 uptake capacity in reversible settings. A partially fluorinated MIL-101(Cr) is stand-alone material with the highest SO2 uptake in chemically stable MOFs. Likewise, metal-free adsorbents like POCs exhibits a reversible SO2 uptake behavior. The SO2 adsorption characteristics of these three structurally and functionally unique adsorbent systems are highly dependent on the binding sites and mode of binding of SO2 molecules. This Review has highlighted the preferential binding sites in these materials to give a full perspective on the field. We anticipate that it will offer valuable information on the progress made towards improving SO2 capture by hybrid systems.

Accelerating Solvent Selection for Type II Porous Liquids.

Type II porous liquids, comprising intrinsically porous molecules dissolved in a liquid solvent, potentially combine the adsorption properties of porous adsorbents with the handling advantages of liquids. Previously, discovery of appropriate solvents to make porous liquids had been limited to direct experimental tests. We demonstrate an efficient screening approach for this task that uses COSMO-RS calculations, predictions of solvent pKa values from a machine-learning model, and several other features and apply this approach to select solvents from a library of more than 11,000 compounds. This method is shown to give qualitative agreement with experimental observations for two molecular cages, CC13 and TG-TFB-CHEDA, identifying solvents with higher solubility for these molecules than had previously been known. Ultimately, the algorithm streamlines the downselection of suitable solvents for porous organic cages to enable more rapid discovery of Type II porous liquids.

An Ultrathin Functional Layer Based on Porous Organic Cages for Selective Ion Sieving and Lithium-Sulfur Batteries.

Thin films with effective ion sieving ability are highly desired in energy storage and conversion devices, including batteries and fuel cells. However, it remains challenging to design and fabricate cost-effective and easy-to-process ultrathin films for this purpose. Here, we report a 300 nm-thick functional layer based on porous organic cages (POCs), a new class of porous molecular materials, for fast and selective ion transport. This solution processable material allows for the design of thin films with controllable thickness and tunable porosity by tailoring cage chemistry for selective ion separation. In the prototype, the functional layer assembled by CC3 can selectively sieve Li+ ions and efficiently suppress undesired polysulfides with minimal sacrifice for the system's total energy density. Separators modified with POC thin films enable batteries with good cycle performance and rate capability and offer an attractive path toward the development of future high-energy-density energy storage devices.

Enhanced Biological Imaging via Aggregation-Induced Emission Active Porous Organic Cages.

Porous organic cages (POCs) have many advantages, including superior microenvironments, good monodispersity, and shape homogeneity, excellent molecular solubility, high chemical stability, and intriguing host-guest chemistry. These properties enable POCs to overcome the limitations of extended porous networks such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). However, the applications of POCs in bioimaging remain limited due to the problems associated with their rigid and hydrophobic structures, thus leading to strong aggregation-caused quenching (ACQ) in aqueous biological media. To address this challenge, we report the preparation of aggregation-induced emission (AIE)-active POCs capable of stimuli responsiveness for enhanced bioimaging. We rationally design a hydrophilic, structurally flexible tetraphenylethylene (TPE)-based POC that is almost entirely soluble in aqueous solutions. This POC's conformationally flexible superstructure allows the dynamic rotation of the TPE-based phenyl rings, thus endowing impressive AIE characteristics for responses to environmental changes such as temperature and viscosity. We employ these notable features in the bioimaging of living cells and obtain good performance, demonstrating that the present AIE-active POCs are suitable candidates for further biological applications.

Sensitive and selective sensor based on porphyrin porous organic cage fluorescence towards copper ion

In present work, a fluorescent porphyrin organic cage sensor PTC-1(2H) for sensitively and selectively detecting divalent copper ion has been introduced. PTC-1(2H) contains the three metal-free units connected by chiral cyclohexanediamine, exhibiting a red-light emission with a broad band at the maximum 641 nm. Among the addition of various metal ions, the emission of PTC-1(2H) has been exclusively and seriously quenched by the addition of divalent copper ions, exhibiting a low limit of detection value of 6.3 nM. A crystal structure of cage with copper ion confirms the complexation of porphyrin N4 cavity and metal ions, revealing the optimized bind position. The special cage structure exhibits the better sensing property than monomeric compound. In addition, a photothermal conversion performance of PTC-1(Cu) has been discovered. These results further enrich the chemistry of porous organic cages.

Racemic Porous Organic Cage Crystal with Selective Gas Adsorption Behaviors

AbstractA mixture containing the reactions solution between 3,3′′,5,5′′‐tetraformyl‐4,4′′‐[1,1′:4′,1′′‐terphenyl]diol (TTD) and two enantiomers of cyclohexanediamine, respectively, affords porous racemic molecular crystal (1). Two kinds of homochiral [3+6] porous organic cage molecules 1 have been clearly disclosed by single crystal X‐ray diffraction analysis, forming one‐dimensional porous supramolecular channels with the narrowest size of 3.5 Å. The intercrossing channels of 1 enable the permanent porosity as well as the selective gas adsorption of acetylene and carbon dioxide over methane.