Redox-active, photoluminescent porous polymers based on spirofluorene-bridged N-heterotriangulenes and their feasibility as organic cathode materials

Novel microporous polymers were synthesized through Yamamoto polymerization of selectively brominated spirofluorene-bridged N-heterotriangulenes. Extensive characterization, including combustion analysis, ToF-SIMS, IR, and Raman spectroscopy, confirmed the elemental composition and integrity of the polymers. The amorphous polymers, observed by scanning electron microscopy as globular particles aggregating into larger structures, exhibited remarkable thermal stability (decomposition temperatures > 400 °C) and BET surface areas up to 690 m2 g-1. Dispersions of the tert-butyl-substituted polymer in different solvents displayed bathochromically shifted emission with remarkable solvatochromism. The polymer is reversibly oxidized at +3.81 V (vs. Li/Li+) in composite electrodes with carbon black and reaches specific capacities up to 26 mA h g-1 and excellent cycling stability when implemented as cathode material in lithium-ion batteries. Our results highlight the potential of spirofluorene-bridged N-heterotriangulenes as versatile building blocks for the development of functional redox-active porous polymers.

Mussel-Inspired Polymer Binders for Organic Electrodes

The development of polymer binders is necessary to meet the growing demands of modern energy storage technologies. While catechol-containing materials are proven successful in silicon anodes, their application in organic batteries remains unexplored. In this contribution, the synthesis of four polymers are described with nearly identical side chain composition but varying backbone structures. The materials are used to investigate the effect of polymer backbone structure on the binding abilities of catechol-containing materials. Comparative analysis with the commonly used polyvinylidene fluoride (PVDF) binder aims to address two critical questions: 1) Can catechol-rich polymers replace PVDF for use in organic cathodes? and 2) Does the choice of polymer backbone affect the performance of the battery?. The investigation reveals that supramolecular interactions, such as π-π stacking and coordination bonding, are pivotal features of catechol binders. Among the catechol-rich polymers, the polyacrylate binder stands out, likely attributed to its high flexibility. Additionally, introducing an oxygen atom into a catechol-rich polynorbornene enhances lithium-ion conductivity and rate performance. Overall, the findings highlight the viability of catechol-containing polymers as organic cathode binders, and that the choice of polymer backbone is a crucial factor for their use as lithium-ion battery binder materials.

A redox-active organic cage as a cathode material with improved electrochemical performance

Organic cages offer numerous opportunities for creating novel materials suitable for a wide range of applications. Among these, energy-related applications are beginning to attract attention. We report here the synthesis of a [3 + 6] trigonal prismatic cage constituted by three redox-active dibenzotetraazahexacene subunits. Cathodes formulated with the organic cage show enhanced performance compared to those formulated with the individual subunits, showing improvements in terms of electrochemical stability, lithium-ion diffusivity, and cathode capacity.

Towards Durable and High-Rate Rechargeable Aluminum Dual-ion Batteries via a Crosslinked Diphenylphenazine-based Conjugated Polymer Cathode

Rechargeable aluminum battery (RAB) is expected to be a promising energy storage technique for grid-scale energy storage. However, the development of RABs is seriously plagued by the lack of suitable cathode materials. Herein, we report two p-type conjugated polymers of L-PBPz and C-PBPz with the same building blocks of diphenylphenazine but different linkage patterns of linear and crosslinked structures as the cathode materials for Al dual-ion batteries. Compared to the linear polymer skeleton in L-PBPz, the crosslinked structure endows C-PBPz with amorphous nature and low dihedral angles of the polymer chains, which severally contribute to the fast diffusion of AlCl4 - with large size and the electron transfer during the redox reaction of diphenylphenazine. As a result, C-PBPz delivers a much better rate performance than L-PBPz. The crosslinked structure also leads to a stable cyclability with over 80000 cycles for C-PBPz. Benefiting from the fast kinetics, meanwhile, the C-PBPz cathode could realize a high redox activity of 117 mAh g-1, corresponding to an areal capacity of 2.30 mAh cm-2, even under a high mass loading of 19.7 mg cm-2 and a low content of 10 wt% conductive agent. These results might boost the development of polymer cathodes for RABs.

Versatile Nitrogen-Centered Organic Redox-Active Materials for Alkali Metal-Ion Batteries

Versatile nitrogen-centered organic redox-active molecules have gained significant attention in alkali metal-ion batteries (AMIBs) due to their low cost, low toxicity, and ease of preparation. Specially, their multiple reaction categories (anion/cation insertion types of reaction) and higher operating voltage, when compared to traditional conjugated carbonyl materials, underscore their promising prospects. However, the high solubility of nitrogen-centered redox active materials in organic electrolyte and their low electronic conductivity contribute to inferior cycling performance, sluggish reaction kinetics, and limited rate capability. This review provides a detailed overview of nitrogen-centered redox-active materials, encompassing their redox chemistry, solutions to overcome shortcomings, characterization of charge storage mechanisms, and recent progress. Additionally, prospects and directions are proposed for future investigations. It is anticipated that this review will stimulate further exploration of underlying mechanisms and interface chemistry through in situ characterization techniques, thereby promoting the practical application of nitrogen-centered redox-active materials in AMIBs.

Long Cycle Life for Rechargeable Lithium Battery using Organic Small Molecule Dihydrodibenzo[c,h][2,6]naphthyridine-5,11-dione as a Cathode after Isoindigo Pigment Isomerization

Sustainability and adaptability in structural design of the organic cathodes present promises for applications in alkali metal ion batteries. Nevertheless, a formidable challenge lies in their high solubility in organic electrolytes, particularly for small molecular materials, impeding cycling stability and high capacity. This study focuses on the design and synthesis of organic small molecules, the isomers of (E)-5,5'-difluoro-[3,3'-biindolinylidene]-2,2'-dione (EFID) and 3,9-difluoro-6,12-dihydrodibenzo [c, h][2,6]naphthyridine-5,11-dione (FBND). While EFID, characterized by a less π-conjugated structure, exhibits subpar cycling stability in lithium-ion batteries (LIBs), intriguingly, another isomer, FBND, demonstrates exceptional capacity and cycling stability in LIBs. FBND delivers a remarkable capacity of 175 mAh g-1 at a current density of 0.05 A g-1 and maintains excellent cycling stability over 2000 cycles, retaining 90% of its initial capacity. Furthermore, an in-depth examination of redox reactions and storage mechanisms of FBND are conducted. The potential of FBND is also explored as an anode in lithium-ion batteries (LIBs) and as a cathode in sodium-ion batteries (SIBs). The FBND framework, featuring extended π-conjugated molecules with an imide structure compared to EFID, proves to be an excellent material template to develop advanced organic small molecular cathode materials for sustainable batteries.

Porous organic materials for iodine adsorption

The nuclear industry will continue to develop rapidly and produce energy in the foreseeable future; however, it presents unique challenges regarding the disposal of released waste radionuclides because of their volatility and long half-life. The release of radioactive isotopes of iodine from uranium fission reactions is a challenge. Although various adsorbents have been explored for the uptake of iodine, there is still interest in novel adsorbents. The novel adsorbents should be synthesized using reliable and economically feasible synthetic procedures. Herein, we discussed the state-of-the-art performance of various categories of porous organic materials including covalent organic frameworks, covalent triazine frameworks, porous aromatic frameworks, porous organic cages, among other porous organic polymers for the uptake of iodine. This review discussed the synthesis of porous organic materials and their iodine adsorption capacity and reusability. Finally, the challenges and prospects for iodine capture using porous organic materials are highlighted.

Stable Hexaazatrinaphthalene-Based Planar Polymer Cathode Material for Organic Lithium-Ion Batteries

Organic materials have garnered intensive focus as a new group of electrodes for lithium-ion batteries (LIBs). However, many reported organic electrodes so far still exhibit unsatisfying cycling stability because of the dissolution in the electrolytes. Herein, a novel azo-linked hexaazatrianphthalene (HATN)-based polymer (AZO-HATN-AQ) is designed and fabricated by the polymerization of trinitrodiquinoxalino[2,3-a:2',3'-c]phenazine (HATNTN) and 2,6-diaminoanthraquinone (DAAQ). The abundant redox-active sites, extended π-conjugated planar conformation, and low energy gap endow the AZO-HATN-AQ electrode with high theoretical capacity, excellent solubility resistance, and fast Li-ion transport. In particular, the fully lithiated AZO-HATN-AQ still keeps the planar structure, contributing to the excellent cycling stability. As a result, AZO-HATN-AQ cathodes show high specific capacity (240 mAh g-1 at 0.05 A g-1), prominent rate capability (98 mAh g-1 at 8 A g-1), and outstanding cycling stability (120 mAh g-1 after 2000 cycles at 4 A g-1 with 85.7% capacity retention) simultaneously. This study demonstrates that rational structure design of the polymer electrodes is an effective approach to achieving excellent comprehensive electrochemical performance.

Hexaazatrinaphthalene-Based Covalent Triazine Framework-Supported Rhodium(III) Complex: A Recyclable Heterogeneous Catalyst for the Reductive Amination of Ketones to Primary Amines

The development of efficient and recyclable heterogeneous catalysts is an important topic. Herein, a rhodium(III) complex Cp*Rh@HATN-CTF was synthesized by the coordinative immobilization of [Cp*RhCl₂]₂ on a hexaazatrinaphthalene-based covalent triazine framework. In the presence of Cp*Rh@HATN-CTF (1 mo l% Rh), a series of primary amines could be obtained via the reductive amination of ketones in high yields. Moreover, catalytic activity of Cp*Rh@HATN-CTF is well maintained during six runs. The present catalytic system was also applied for the large scale preparation of a biologically active compound. It would facilitate the development of CTF-supported transition metal catalysts for sustainable chemistry.

Click postsynthesis of microporous organic network@silica composites for reversed-phase/hydrophilic interaction mixed-mode chromatography

Recently, the good physical and chemical properties, well-defined pore architectures, and designable topologies have made microporous organic networks (MONs) excellent potential candidates in high-performance liquid chromatography (HPLC). However, their superior hydrophobic structures restrict their application in the reversed-phase mode. To solve this obstacle and to expand the application of MONs in HPLC, we realized the thiol-yne "click" postsynthesis of a novel hydrophilic MON-2COOH@SiO₂-MER (MER denotes mercaptosuccinic acid) microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography. SiO₂ was initially decorated with MON-2COOH using 2,5-dibromoterephthalic acid and tetrakis(4-ethynylphenyl)methane as monomers, and MER was then grafted via thiol-yne click reaction to yield MON-2COOH@SiO₂-MER microspheres (5 μm) with a pore size of ~1.3 nm. The -COOH groups in 2,5-dibromoterephthalic acid and the post-modified MER molecules considerably improved the hydrophilicity of pristine MON and enhanced the hydrophilic interactions between the stationary phase and analytes. The retention mechanisms of the MON-2COOH@SiO₂-MER packed column were fully discussed with diverse hydrophobic and hydrophilic probes. Benefiting from the numerous -COOH recognition sites and benzene rings within MON-2COOH@SiO₂-MER, the packed column exhibited good resolution for the separation of sulfonamides, deoxynucleosides, alkaloids, and endocrine-disrupting chemicals. A column efficiency of 27,556 plates per meter was obtained for the separation of gastrodin. The separation performance of the MON-2COOH@SiO₂-MER packed column was also demonstrated by comparing with those of MON-2COOH@SiO₂, commercial C18, ZIC-HILIC, and bare SiO₂ columns. This work highlights the good potential of the thiol-yne click postsynthesis strategy to construct MON-based stationary phases for mixed-mode chromatography.

Design and Synthesis of Bisulfone-Linked Two-Dimensional Conjugated Microporous Polymers for CO2 Adsorption and Energy Storage

We have successfully synthesized two types of two-dimensional conjugated microporous polymers (CMPs), Py-BSU and TBN-BSU CMPs, by using the Sonogashira cross-coupling reaction of BSU-Br2 (2,8-Dibromothianthrene-5,5′,10,10′-Tetraoxide) with Py-T (1,3,6,8-Tetraethynylpyrene) and TBN-T (2,7,10,15-Tetraethynyldibenzo[g,p]chrysene), respectively. We characterized the chemical structure, morphology, physical properties, and potential applications of these materials using various analytical instruments. Both Py-BSU and TBN-BSU CMPs showed high thermal stability with thermal decomposition temperatures (Td10) up to 371 °C and char yields close to 48 wt%, as determined by thermogravimetric analysis (TGA). TBN-BSU CMPs exhibited a higher specific surface area and porosity of 391 m2 g−1 and 0.30 cm3 g−1, respectively, due to their large micropore and mesopore structure. These CMPs with extended π-conjugated frameworks and high surface areas are promising organic electroactive materials that can be used as electrode materials for supercapacitors (SCs) and gas adsorption. Our experimental results demonstrated that the TBN-BSU CMP electrode had better electrochemical characteristics with a longer discharge time course and a specific capacitance of 70 F g−1. Additionally, the electrode exhibited an excellent capacitance retention rate of 99.9% in the 2000-cycle stability test. The CO2 uptake capacity of TBN-BSU CMP and Py-BSU CMP were 1.60 and 1.45 mmol g−1, respectively, at 298 K and 1 bar. These results indicate that the BSU-based CMPs synthesized in this study have potential applications in electrical testing and CO2 capture.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Reactions of polyaromatic molecules in crystals under electron beam of the transmission electron microscope

Reactivity of a series of related molecules under the 80 keV electron beam have been investigated and correlated with their structures and chemical composition. Hydrogenated and halogenated derivatives of hexaazatrinaphthylene, coronene, and phthalocyanine were prepared by sublimation in vacuum to form solventless crystals then deposited onto transmission electron microscopy (TEM) grids. The transformation of the molecules in the microcrystals were triggered by an 80 keV electron beam in the TEM and studied using correlated selected area electron diffraction, conventional bright field imaging, and energy dispersive X-ray spectroscopy. The critical fluence (ē nm^-2) required to cause a disappearance of the diffraction pattern was recorded and used as a measure of the reactivity of the molecules. The same electron flux (10² ē nm^-2 s^-1) was used throughout. Fully halogenated molecules were found to be the most stable and did not change significantly under our experimental conditions, followed by fully hydrogenated molecules with critical fluences of 10⁴ ē nm^-2. Surprisingly, semi-halogenated molecules that contained an equal number of hydrogen and halogen atoms were found to be the least stable, with critical fluences an order of magnitude lower at 10³ ē nm^-2. This is attributed to elimination of H-X (where X = F or Cl), followed by polymerisation of aryne / aryl radicals within the crystal. The critical fluence for the semi-fluorinated hexaazatrinaphthylene is the lowest as the presence of water molecules in its crystal lattice significantly decreased the stability of the organic molecules under the electron beam. Semi-halogenation reduces the beam stability of organic molecules compared to the parent hydrogenated molecule, thus providing the chemical guidance for design of electron beam stable materials. Understanding of molecular reactivity in the electron beam is necessary for advancement of molecular imaging and analysis methods by the TEM, molecular materials processing, and electron beam-driven synthesis of novel materials.

Molecular and Morphological Engineering of Organic Electrode Materials for Electrochemical Energy Storage

Organic electrode materials (OEMs) can deliver remarkable battery performance for metal-ion batteries (MIBs) due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental costs. Therefore, OEMs are promising, green alternatives to the traditional inorganic electrode materials used in state-of-the-art lithium-ion batteries. Before OEMs can be widely applied, some inherent issues, such as their low intrinsic electronic conductivity, significant solubility in electrolytes, and large volume change, must be addressed. In this review, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to address these challenges by using molecular and morphological engineering are thoroughly summarized and discussed. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, can enhance the electrochemical performance, including its specific capacity (such as the voltage output and the charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (including 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance their electron/ion diffusion kinetics and stabilize their electrode structure. In summary, molecular and morphological engineering can offer practical paths for developing advanced OEMs that can be applied in next-generation rechargeable MIBs.

Graphical abstract

Synthetic Control of Electronic Property and Porosity in Anthraquinone-Based Conjugated Polymer Cathodes for High-Rate and Long-Cycle-Life Na-Organic Batteries

Redox-active carbonyl-containing compounds have received extensive attention as cathode materials for sodium-ion batteries (SIBs) because of their excellent attributes, including elemental sustainability, high theoretical capacity, diverse structures, and tunable properties. However, the storage of Na⁺ in most carbonyl-based cathode materials is plagued by the low capacity, unsatisfying rate performance, and short cycling life. Herein, we develop a series of anthraquinone-based conjugated polymer cathodes consisting of anthraquinone and benzene with different linking patterns. It reveals that the linkage sites on benzene ring could affect the electronic structures of the resulting polymers and thus their charge-storage capabilities. The 1,2,4,5-linkage on benzene leads to a high surface area, a narrow band gap, and the lowest unoccupied molecular orbital for the resulting polymer PBAQ-3. As a cathode for SIBs, it delivers a high capacity of around 200 mAh g^-1 and excellent rate performance (105 mAh g^-1 at 200 C) as well as stable cycling with a capacity retention of 95.8% after 1000 cycles at 0.05 A g^-1 and 83.1% after 40000 cycles at 3 A g^-1. Our findings highlight the influence of linking patterns of the building blocks on the electrochemical performance of organic electrodes.

π-Conjugated Hexaazatrinaphthylene-Based Azo Polymer Cathode Material Synthesized by a Reductive Homocoupling Reaction for Organic Lithium-Ion Batteries

A novel hexaazatrinaphthylene-based (HATN) azo polymer (PAH) was synthesized from a newly designed tri-nitro compound trinitrodiquinoxalino[2,3-a:2',3'-c]phenazine (HATNTN) through a Zn-induced reductive homocoupling reaction and used as a cathode material for lithium-ion batteries (LIBs). The integration of redox-active HATN units and azo linkages can improve the specific capacity, rate performance, and cycling stability of the PAH cathode. The control LIBs were assembled from HATNTN, in which HATNTN can be electrochemically reduced to an HATN-based azo polymer. Compared with the HATNTN cathode, the PAH cathode delivers higher specific capacities with much-improved cycling stability (97 mA h g^-1 capacity retention after 1500 cycles at 500 mA g^-1, which is around 28 times that of the HATNTN cathode) and considerably better rate performance (118 mA h g^-1 at 2000 mA g^-1, which is around 90 times that of the HATNTN cathode), simultaneously. This work provides a chemical polymerization strategy to construct extended π-conjugated azo polymers with multiple redox centers from nitro compounds for developing high-performance LIBs.

Macroscale Conjugated Microporous Polymers: Controlling Versatile Functionalities Over Several Dimensions

Since discovered in 2007, conjugated microporous polymers (CMPs) have been developed for numerous applications including gas adsorption, sensing, organic and photoredox catalysis, energy storage, etc. While featuring abundant micropores, the structural rigidity derived from CMPs' stable π-conjugated skeleton leads to insolubility and thus poor processability, which severely limits their applicability, e.g., in CMP-based devices. Hence, the development of CMPs whose structure can not only be controlled on the micro- but also on the macroscale have attracted tremendous interest. In conventional synthesis procedures, CMPs are obtained as powders, but in recent years various bottom-up synthesis strategies have been developed, which yield CMPs as thin films on substrates or as hybrid materials, allowing to span length scales from individual conjugated monomers to micro-/macrostructures. This review surveys recent advances on the construction of CMPs into macroscale structures, including membranes, films, aerogels, sponges, and other architectures. The focus is to describe the underlying fabrication techniques and the implications which follow from the macroscale morphologies, involving new chemistry and physics in such materials for applications like molecular separation/filtration/adsorption, energy storage and conversion, photothermal transformation, sensing, or catalysis.

Controllable Synthesis of 1, 3, 5-tris (1H-benzo[d]imidazole-2-yl) Benzene-Based MOFs

The growing interest in metal–organic frameworks (MOFs) in both industrial and scientific circles has increased in the last twenty years, owing to their crystallinity, structural versatility, and controlled porosity. In this study, we present three novel MOFs obtained from the 1, 3, 5-tris (1H-benzo[d]imidazole-2-yl) benzene (TIBM) organic linker. The formed TIBM crystal powders were characterized by scanning electron microscopy (SEM) to estimate the morphology of the particles, powder X-ray diffraction (XRD) to confirm the crystal structure, Brunauer–Emmett–Teller (BET) method for structural analysis, and thermogravimetric measurements to examine the thermal stability. The TIBM-Cu MOF showed excellent CO2 (3.60 mmol/g) adsorption capacity at 1 bar and 298 K, because of the open Cu site, compared to TIBM-Cr (1.6 mmol/g) and TIBM-Al (2.1 mmol/g). Additionally, due to the high porosity (0.3–1.5 nm), TIBM-Cu MOF showed a considerable CO2/N2 selectivity (53) compared to TIBM-Al (35) and TIBM-Cr (10).

Tailored amino/hydroxyl bifunctional microporous organic network for efficient stir bar sorptive extraction of parabens and flavors from cosmetic and food samples

As an effective sample pretreatment approach, stir bar sorptive extraction (SBSE) has shown great prospects in static microextraction and selective enrichment. In this work, bifunctional microporous organic network (B-MON) with the coexistence of amino and hydroxyl groups was firstly designed and synthesized as a novel coating for efficient SBSE of parabens and flavors in combination with high-performance liquid chromatography coupled with photodiode array detection (HPLC-PDA). Linked by covalent bonds to form an extension of the aromatic ring skeleton, B-MON was a tailored adsorbent featured by porous structure and abundant hydrogen bonding sites for analytes with benzene/naphthalene rings and OH/COOH groups. The extraction and desorption parameters were evaluated in detail. Under the optimized conditions, the proposed B-MON-SBSE-HPLC-PDA method offered good linearity (0.10-100 μg L^-1) with correlation coefficients R² ≥ 0.995, low limits of detection (0.010-0.035 μg L^-1) and limits of quantification (0.035-0.115 μg L^-1), and favorable enrichment factors (40-49). Furthermore, the developed method has been applied to the analysis of parabens and flavors in cosmetic and food samples with recoveries ranging from 80.4 to 109.6%. This method was also feasible to extract the analytes with benzene/naphthalene rings and OH/COOH groups, such as the plant growth regulators and non-steroidal anti-inflammatory drugs. The present study provided a new way to synthesize bifunctional MONs for SBSE of trace analytes in complex samples.

Triazine-Based Conjugated Microporous Polymers for Efficient Hydrogen Production

Developing visible-light-active porous organic polymers with high photocatalytic efficiency is highly desirable. Here, two triazine-based conjugated microporous polymers were synthesized. The structures were controllably adjusted to explore the structure-photocatalytic activity relationship. T-CMP-1 containing more triazine units exhibited a hydrogen evolution rate of 3214.3 μmol h^-1 g^-1, much higher than that of T-CMP-2 (242.1 μmol h^-1 g^-1). The increasing contents of triazine units bring better hydrogen evolution efficiency.

Rational design of bifunctional conjugated microporous polymers

Conjugated microporous polymers (CMPs) are an emerging class of porous organic polymers that combine π-conjugated skeletons with permanent micropores. Since their first report in 2007, the enormous exploration of linkage types, building units, and synthetic methods for CMPs have facilitated their potential applications in various areas, from gas separations to energy storage. Owning to their unique construction, CMPs offer the opportunity for the precise design of conjugated skeletons and pore environment engineering, which allow the construction of functional porous materials at the molecular level. The capability to chemically alter CMPs to targeted applications allows for the fine adaptation of functionalities for the ever-changing environments and necessities. Bifunctional CMPs are a branch of functionalized CMPs that have caught the interest of researchers because of their inherent synergistic systems that can expand their applications and optimize their performance. This review discusses the rational design and synthesis of bifunctional CMPs and summarizes their advanced applications. To conclude, our own perspective on the research prospects of these types of materials is outlined.

The Synthesis of Hexaazatrinaphthylene-Based 2D Conjugated Copper Metal-Organic Framework for Highly Selective and Stable Electroreduction of CO2 to Methane

2D conjugated MOFs have attracted significant interests in recent years owing to their special structural features and promising physical and chemical properties. These intriguing attributes, to a large extent, stem from the nature of incorporated ligands. The available ligands for the construction of 2D conjugated MOFs are still limited, especially those that have heteroatoms included and exposed to the pores. In this work, we designed and synthesized a highly symmetric hexaazatrinaphthylene (HATNA)-based ligand with two different coordination sites. Through selective coordination, a highly crystalline and porous 2D conjugated copper metal-organic framework was constructed. Due to the synergic effects of HATNA and copper catecholate node, this HATNA-based 2D conjugated MOF can mediate the electrocatalytic reduction of CO₂ to methane with high selectivity of 78 % at high current density of 8.2 milliamperes per square centimetre (mA cm^-2 ) for long durability over 12 hours.

Pyrrole-Based Conjugated Microporous Polymers as Efficient Heterogeneous Catalysts for Knoevenagel Condensation

Conjugated microporous polymers (CMPs) with robust architectures, facilely tunable pore sizes and large specific surface areas have emerged as an important class of porous materials due to their demonstrated prospects in various fields, e.g. gas storage/separation and heterogeneous catalysis. Herein, two new pyrrole-based CMPs with large specific surface areas and good stabilities were successfully prepared by one-step oxidative self-polycondensation of 1,2,4,5-tetra (pyrrol-2-ly)benzene or 1,3,5-tri (pyrrol-2-ly)benzene, respectively. Interestingly, both CMPs showed very high catalytic activity toward Knoevenagel condensation reaction, which was attributed to the inherent pore channels, high specific surface areas and abundant nitrogen sites within CMPs. Additionally, both CMPs displayed excellent recyclability with negligible degradation after 10 cycles. This work provides new possibilities into designing novel nitrogen-rich high-performance heterogeneous catalysts.

Regular Polymeric Microspheres with Highly Developed Internal Structure and Remarkable Thermal Stability

In this study, the synthesis and characterization of permanently porous polymeric microspheres was presented. The microspheres were obtained via suspension polymerization using diverse functional monomers, such as 4,4′-bis(methacryloyloxymethylphenyl)sulphone, 1,4-bis(methacryloyloxymethyl)benzene, 4,4′-bis(methacryloyloxymethylphenyl)methane, N-vinylpyrrolidone, ethylene glycol dimethacrylate, and divinylbenzene as a co-monomer. As porogenic solvents, toluene and chlorobenzene were applied. The main aim of the research was to synthesize polymers having a highly developed internal structure and a good thermal stability. The synthesized materials were characterized by ATR-FTIR, scanning electron microscopy, a size distribution analysis, a low-temperature nitrogen adsorption–desorption method, differential scanning calorimetry, and thermogravimetry coupled with FTIR and inverse gas chromatography. It was found that, depending on the functional monomer, regular microspheres with a specific surface area in the range of 418–746 m²/g can be successfully synthesized. Moreover, all the synthesized copolymers showed a good thermal stability. In helium, they exhibited 5% mass losses at temperatures over 300 °C, whereas in air these values were only slightly lower. In addition, the presence of miscellaneous functional groups promoted diverse kinds of interactions. Therefore, the microspheres can be possibly use in many adsorption techniques including high temperature processes.

Redox Donor-Acceptor Conjugated Microporous Polymers as Ultralong-Lived Organic Anodes for Rechargeable Air Batteries

Herein, we explore a new redox donor-acceptor conjugated microporous polymer (AQ-CMP) by utilizing anthraquinone and benzene as linkers via C-C linkages and demonstrate the first use of CMP as ultralong-lived anodes for rechargeable air batteries. AQ-CMP features an interconnected octupole network, which affords not only favorable electronic structure for enhanced electron transport and n-doping activity compared to linear counterpart, but also high density of active sites for maximizing the formula-weight-based redox capability. This coupled with highly cross-linked and porous structure endows AQ-CMP with a specific capacity of 202 mAh g^-1 (96 % of theoretical capacity) at 2 Ag^-1 and ≈100 % capacity retention over 60000 charge/discharge cycles. The assembled CMP-air full cell shows a stable and high capacity with full capacity recovery after only refreshing cathodes, while the decoupled electrolyte and cathode design boosts the discharge voltage and voltage efficiency to ≈1 V and 87.5 %.

Conjugated Microporous Polymers Doped with Rare Earth Ions: Synthesis, Characterization and Energy Transfer

In order to study the energy transfer between the conjugated polymer and rare-earth ions, a series of conjugated microporous polymers (CMPs) CMP-COOH@M (M=Eu³⁺ , Tb³⁺ , La³⁺ , and Sm³⁺ ) with different kinds of rare-earth ions was synthesized, in which the conjugated networks can effectively improve the luminescence of rare-earth ions due to the effective energy transfer from the CMP network to the rare-earth ions centers. The absolute quantum yield of CMP-COOH (Φ_FL ) is 29.1 %, while the Φ_FL value of CMP-COOH@Eu, CMP-COOH@Tb, CMP-COOH@La, and CMP-COOH@Sm is 9.4, 8.6, 14.3, and 9.1 %, respectively. This result indicates that the quantum efficiency of CMPs network is 1/2-1/3 of the original one due to the coordination of rare earth ions, that is, rare-earth ions can be recognized as fine modulators to adjust the emission color of CMPs in a controlled manner through controlling the species of rare-earth ions.

Electroactive Covalent Organic Frameworks: Design, Synthesis, and Applications

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with tailorable compositions, porosities, functionalities, and intrinsic chemical stability. The incorporation of electroactive moieties in the structure transforms COFs into electroactive materials with great potential for energy-related applications. Herein, the recent advances in the design and use of electroactive COFs as capacitors, batteries, conductors, fuel cells, water-splitting, and electrocatalysis are addressed. Their remarkable performance is discussed and compared with other porous materials; hence, perspectives in the development of electroactive COFs are presented.

Construction of Thiazolo[5,4-d]thiazole-based Two-Dimensional Network for Efficient Photocatalytic CO2 Reduction

The efficient conversion of CO₂ to chemical fuels driven by solar energy is still a challenging research area in photosynthesis, in which the conversion efficiency greatly relies on photocatalytic coenzyme NADH regeneration. Herein, a photocatalyst/biocatalyst synergetic system based on a conjugated microporous polymer (CMP) was prepared for sustainable and highly selective photocatalytic reduction of CO₂ to methanol. Two thiazolo[5,4-d]thiazole-linked CMPs (TZTZ-TA and TZTZ-TP) were designed and synthesized as photocatalysts. Slight skeleton modification led to a great difference in their photocatalytic performance. Triazine-based TZTZ-TA exhibited an unprecedentedly high NADH regeneration efficiency of 82.0% yield within 5 min. Furthermore, the in situ photocatalytic NADH regeneration system could integrate with three consecutive enzymes for efficient conversion of CO₂ into methanol. This CMP-enzyme hybrid system provides a new avenue for accomplishing the liquid sunshine from CO₂.

Molecular Expansion for Constructing Porous Organic Polymers with High Surface Areas and Well-Defined Nanopores

Construction of porous organic polymers (POPs) with high surface areas, well-defined nanopores, and excellent stability remains extremely challenging because of the unmanageable reaction process. Until now, only a few reported POPs have Brunauer-Emmett-Teller (BET) surface areas (S_BET ) exceeding 3000 m²  g^-1 . Herein, we demonstrate a molecular expansion strategy to integrate high surface areas, large nanopore sizes, and outstanding stability into POPs. A series of hyper-crosslinked conjugated polymers (HCCPs) with exceptional porosity are synthesized through this strategy. Specially, HCCP-6 and HCCP-11 exhibit the highest surface areas (S_BET >3000 m²  g^-1 ) and excellent total pore volumes (up to 3.98 cm³  g^-1 ) among these HCCPs. They present decent total CH₄ storage capacities of 491 and 421 mg g^-1 at 80 bar and 298 K, respectively. Meanwhile, they are highly stable in harsh environments. The facile and general molecular expansion strategy would lead to improved synthetic routes of POPs for desired functions.

Exploiting Polythiophenyl-Triazine-Based Conjugated Microporous Polymer with Superior Lithium-Storage Performance

Conjugated microporous polymers (CMPs) have been heralded as promising energy-storage materials with advantages such as chemical flexibility, porous structure, and environmentally friendliness. Herein, a novel conjugated microporous polymer was synthesized by integrating triazine, thiophene, and benzothiadiazole into a polymer skeleton, and the Li⁺ -storage performance for the as-synthesized polymer anode in Li-ion batteries (LIBs) was investigated. Benefiting from the inherent large surface area, plentiful redox-active units, and hierarchical porous structure, the polymer anode delivered a high Li⁺ storage capacity up to 1599 mAh g^-1 at a current rate of 50 mA g^-1 with an excellent rate behavior (363 mAh g^-1 at 5 A g^-1 ) and a long-term cyclability of 326 mAh g^-1 over 1500 cycles at 5 A g^-1 , implying that the newly developed polymer anode offers a great prospect for next-generation LIBs.

Advances in Conjugated Microporous Polymers

Conjugated microporous polymers (CMPs) are a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. Since their discovery in 2007, CMPs have become established as an important subclass of porous materials. A wide range of synthetic building blocks and network-forming reactions offers an enormous variety of CMPs with different properties and structures. This has allowed CMPs to be developed for gas adsorption and separations, chemical adsorption and encapsulation, heterogeneous catalysis, photoredox catalysis, light emittance, sensing, energy storage, biological applications, and solar fuels production. Here we review the progress of CMP research since its beginnings and offer an outlook for where these materials might be headed in the future. We also compare the prospect for CMPs against the growing range of conjugated crystalline covalent organic frameworks (COFs).

Nitrogen-Linked Hexaazatrinaphthylene Polymer as Cathode Material in Lithium-Ion Battery

Nitrogen-linked hexaazatrinaphthylene polymer (N² -HATN) as organic cathode material with low HOMO-LOMO gap was synthesized and was observed to possess reversible high capacity and unexpected long-term cycling stability. The pre-treated N² -HATN and pRGO combination demonstrated good structure compatibility and the resultant cathode exhibited a constant increment of capacity during the redox cycles. The initial capacity at 0.05 A g^-1 was 406 mA h^-1  g^-1 , and increased to 630 mA h^-1  g^-1 after 70 cycles. At 0.5 A g^-1 discharging rate, the capacity increased from an initial value of 186 mA h^-1  g^-1 to 588 mA h^-1  g^-1 after 1600 cycles. The pseudocapacitance-type behavior is postulated to be attributed to the structure compatibility between the active material and pRGO.

Exceptionally Stable Microporous Organic Frameworks with Rigid Building Units for Efficient Small Gas Adsorption and Separation

Three microporous organic frameworks (hereafter denoted as MPOF-Ads) based on a rigid adamantane core have been successfully synthesized via Sonogashira-Hagihara polycondensation coupling in high yields, 83.7-94.6%. The obtained amorphous MPOF-Ads networks have high Brunauer-Emmett-Teller surface areas (up to 737.3 m² g^-1), narrow pore size distribution (0.95-1.06 nm), and superior thermal (the initial decomposition temperature T_5% under an N₂ atmosphere can reach 410 °C) and chemical stability (no apparent degradation in common organic solvents or strong acid/base solutions after 7 days). At 273 K and 1.0 bar, these MPOF-Ads networks present good uptake capacities for small gas molecules (13.9 wt % CO₂ and 1.66 wt % CH₄) for which the presence of high surface area, predominant microporosity, and narrow pore size distribution are beneficial. In addition, the as-prepared MPOF-Ads networks possess moderate isosteric heats for CO₂ (Q_st = 19.5-30.3 kJ mol^-1) and show desired CO₂/N₂ and CO₂/CH₄ selectivity (36.3-38.4 and 4.1-4.3 based on Henry's law and 17.88-24.92 and 4.24-5.70 based on ideal adsorbed solution theory, respectively). With the demonstrated properties, the synthesized MPOF-Ads networks display potential for small gas storage and separation that can be used in harsh environments because of their superior physical and chemical stability.

A conjugated microporous polymer as a recyclable heterogeneous ligand for highly efficient regioselective hydrosilylation of allenes

Pyridines containing adjacent C[triple bond, length as m-dash]C bonds were utilized as ligand units and integrated into the skeleton of conjugated microporous polymers. The resultant Pd-CMP-1 was first applied as a highly efficient heterogeneous catalytic system for Pd-catalyzed allene hydrosilylation towards a wide range of allenes to produce branched allylsilanes with high regioselectivity. The ligand units of the polymer, along with the confinement effect of the porous structure, jointly regulated the regioselectivity. The parts-per-million (ppm) levels of Pd, coordinated with the recyclable heterogeneous ligand, show promise for industrial applications. This work opens a new front of using CMP as an intriguing platform for developing highly efficient catalysts to control the regioselectivities in allene hydrosilylation.

Covalent Organic Frameworks: Design, Synthesis, and Functions

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure-function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.

Stable, Dual Redox Unit Organic Electrodes

The development of organic materials for electrochemical energy storage has attracted great attention because of their high natural abundance and relatively low toxicity. The bulk of these studies focus on small molecules, polymers, or porous/framework-type materials that employ one type of redox moiety. Here, we report the synthesis and testing of organic materials that incorporate two distinct types of redox units: triptycene-based quinones and perylene diimides. We examine this "dual redox" concept through the synthesis of both frameworks and small molecule model compounds with the redox units positioned at the vertices and connection points. Such a design increases the theoretical capacity of the material. It also imparts high stability because both examples are relatively rigid and highly insoluble in the electrolyte. Lithium-ion batteries consisting of the framework and the small molecule have an excellent cycling retention of 75 and 77%, respectively, over 500 cycles at 1 C. Our work emphasizes the advantages of using multiple redox units in the design of the cathodic materials and redox-active triptycene linkages to achieve high cycling stability.