Two-dimensional Polymer Research Articles

Crystalline Covalent Triazine Frameworks and 2D Triazine Polymers: Synthesis and Applications.

ConspectusCovalent triazine frameworks (CTFs) are a novel class of nitrogen-rich conjugated porous organic materials constructed by robust and functional triazine linkages, which possess unique structures and excellent physicochemical properties. They have demonstrated broad application prospects in gas/molecular adsorption and separation, catalysis, energy conversion and storage, etc. In particular, crystalline CTFs with well-defined periodic molecular network structures and regular pore channels can maximize the utilization of the features of CTFs and promote a deep understanding of the structure-property relationship. However, due to the poor reversibility of the basic reaction for constructing the triazine unit and the traditional harsh synthesis conditions, it remains a considerable challenge to synthesize crystalline CTFs with diverse molecular structures, and there is still a significant lack of understanding of their polymerization mechanism, which limits their precise structural design, large-scale preparation, and practical applications. As the basic building block of bulk crystalline CTFs, two-dimensional triazine polymers (2D-TPs) which ideally have single-atom thickness have also aroused intensive interest due to their ultrathin 2D sheet morphology with structural flexibility, a fully exposed molecular plane and active sites, and excellent dispersibility and processability. However, the efficient and scalable production of high-quality 2D-TPs and the investigation of their unique properties and functions remain largely unexplored.In this Account, we summarize our recent contributions to the synthesis and application exploration of crystalline CTFs and 2D-TPs. We first introduce the design, synthesis, and polymerization mechanism of the crystalline CTFs. In order to synthesize high-quality CTFs, we have successively used a series of new synthetic methods including a solution polymerization strategy, microwave-assisted superacid-catalyzed polymerization strategy, polyphosphoric acid-catalyzed polymerization strategy, and solvent-free FeCl3-catalyzed polymerization strategy, achieving the production of highly crystalline layered CTFs from the gram level to the hundred-gram level and then to the kilogram level and realizing new CTF molecular structures. We also reveal a direct ordered 2D polymerization mechanism that provided meaningful guidance for the controllable preparation of functional CTFs. Next, we introduce the design, synthesis, and formation mechanism of 2D-TPs. We have developed effective bottom-up and top-down strategies to prepare 2D-TPs for different needs. On one hand, we have established the dynamic interface polymerization method, the monomer-dependent method, and the solvent-free salt-catalyzed polymerization strategy for the direct synthesis of ultrathin 2D-TPs with thickness down to the single-layer limit and provided important insights into the 2D polymerization mechanism. On the other hand, we have opened up the physical and chemical exfoliation of crystalline layered CTFs such as liquid sonication and ball milling exfoliation and covalent and noncovalent modification exfoliation for the large-scale production of 2D-TPs. Then, we present the application progress of crystalline CTFs and 2D-TPs in various batteries, photo/electrocatalysis, and adsorbents with an emphasis on their unique and outstanding performance and structure-property relationship. Lastly, the main challenges faced by crystalline CTFs and 2D-TPs in practical applications and future research directions are discussed in detail. We hope that this Account will provide valuable insights and practical strategies for promoting the development of functional organic framework materials and 2D polymer materials.

Self-Organized Protonic Conductive Nanochannel Arrays for Ultra-High-Density Data Storage.

While the highest-performing memristors currently available offer superior storage density and energy efficiency, their large-scale integration is hindered by the random distribution of filaments and nonuniform resistive switching in memory cells. Here, we demonstrate the self-organized synthesis of a type of two-dimensional protonic coordination polymers with high crystallinity and porosity. Hydrogen-bond networks containing proton carriers along its nanochannels enable uniform resistive switching down to the subnanoscale range. Leveraging such nanochannel arrays, we achieve logic operations of graphical gate circuits with negligible leakage and sneak path currents over areas ranging from 0.5 μm × 0.5 μm to 20 nm × 20 nm, providing the smallest building blocks to date for large-scale integration. The nonvolatile resistive switching exhibits high mobility (∼0.309 cm2 V-1 s-1), a large on/off ratio (∼103), and ultrahigh-density data storage (∼645 Tbit/in2), even within a trilayer (∼4.01 nm). An ultrahigh-precision artificial retina with integrated convolutional neural network calculations is demonstrated, enabling facial and color recognition capabilities.

Mechanically interlocked two-dimensional polymers.

Mechanical bonds arise between molecules that contain interlocked subunits, such as one macrocycle threaded through another. Within polymers, these linkages will confer distinctive mechanical properties and other emergent behaviors, but polymerizations that form mechanical bonds efficiently and use simple monomeric building blocks are rare. In this work, we introduce a solid-state polymerization in which one monomer infiltrates crystals of another to form a macrocycle and mechanical bond at each repeat unit of a two-dimensional (2D) polymer. This mechanically interlocked 2D polymer is formed as a layered solid that is readily exfoliated in common organic solvents, enabling spectroscopic characterization and atomic-resolution imaging using advanced electron microscopy techniques. The 2D mechanically interlocked polymer is easily prepared on multigram scales, which, along with its solution processibility, enables the facile fabrication of composite fibers with Ultem that exhibit enhanced stiffness and strength.

Recent progress in two-dimensional polymer materials: interfacial synthesis and applications

Abstract As a new two-dimensional polymer synthetic material, two-dimensional polymers (2DPs) not only have the advantages of high specific surface area and high transparency of two-dimensional materials, but also have the advantages of high mechanical strength and easy processing of polymer materials. Therefore, 2DPs are widely used and have become one of the indispensable materials today. However, there are still challenges in preparing 2DPs using traditional methods. Among the various synthesis strategies, the interfacial synthesis methods with the advantages of simple operation and high crystallinity have become typical method for preparing 2DPs. In this review, we first summarize the types of interface synthesis methods and the latest research progress. Secondly, the 2DPs applications in optoelectronic devices, membrane separation, sensor, electrical device and batteries, etc. are introduced. Finally, we summarize and prospect the existing challenges and future research directions based on the current research status of 2DPs.

A Crystalline 3D Supramolecular Polymer Constructed by Clamparene-Based Controllable Self-Assembly and Its Application in Photothermal Conversion.

The development of well-defined three-dimensional supramolecular polymers presents significant challenges, particularly in achieving crystalline state structures. This study addresses this challenge by presenting the construction of a crystalline three-dimensional supramolecular polymer through the self-assembly of clamparene (CLP) and a naphthalene diimide derivative (NDIOH) in the solid state. The hierarchical self-assembly progresses from one-dimensional linear supramolecular polymers to two-dimensional supramolecular polymers and ultimately to a crystalline three-dimensional supramolecular polymer. Moreover, the prepared crystalline three-dimensional supramolecular polymer demonstrates effective photothermal conversion. This work advances the understanding and design of functional three-dimensional supramolecular polymers in the crystalline state.

Block Architectures in 2D Polymer Networks Fabricated via Sequential Copolymerization in a Metal-Organic Framework.

Two-dimensional (2D) polymer network monolayers with novel block architectures were fabricated via sequential copolymerization within a pillared-layer metal-organic framework (MOF) that served as the reaction template. The MOF provides a confined 2D nanospace, restricting the crosslinking copolymerization of vinyl monomers to two dimensions. Sequential crosslinking copolymerization of methyl methacrylate and styrene, regulated by the reversible addition-fragmentation chain transfer (RAFT) process, resulted in the formation of 2D block architectures with 'patchy' domains consisting of crosslinked poly(methyl methacrylate) and polystyrene segments. Atomic force microscopy revealed that the resulting block monolayers exhibited varied morphologies on substrates, attributed to their intrinsic flexibility in 2D conformation, which facilitated microphase separation of the 2D segments within monolayers, leading to the unique aggregation morphologies. The unprecedented block topology in 2D polymeric monolayers presented in this study introduces a novel strategy for designing 2D polymeric nanomaterials with flexible yet anisotropic properties.

Single-Component Coordination Polymers with Excitation Wavelength- and Temperature-Dependent Long Persistent Luminescence toward Multilevel Information Security.

Metal-organic hybrid materials with long persistent luminescence (LPL) properties have attracted a lot of attention due to their enormous potential for applications in information encryption, anticounterfeiting, and other correlation fields. However, achieving multimodal luminescence in a single component remains a significant challenge. Herein, we report two two-dimensional LPL coordination polymers: {[Zn2(BA)2(BIMB)2]·2H2O}n (1) and {[Cd(BA)(BIMB)]·3H2O}n (2) (BIMB = 1,3-bis(imidazol-1-yl)benzene; BA = butanedioic acid). Their LPL colors can be adjusted by the excitation wavelength or temperature variation in a single-component coordination polymer, achieving multimode color adjustment from green to orange or blue to yellow. X-ray single-crystal diffraction analysis and theoretical calculations demonstrate that abundant intermolecular interactions, ligand-to-ligand charge transfer (LLCT) transitions, and heavy atom effects of the central metal can realize multicolor afterglow. This work provides a convenient strategy for new pattern multicolor LPL materials and may also inspire new ideas for advanced information encryption technologies.

Flexible Solid Electrolytes from Two-Dimensional Metal Carbide, Polymer, and Ionic Covalent Organic Frameworks

Flexible Solid Electrolytes from Two-Dimensional Metal Carbide, Polymer, and Ionic Covalent Organic Frameworks

A novel silver(I) two-dimensional coordination polymer of thiophosphoric triamide ligand with two different coordination modes: Experimental, theoretical and molecular docking study

A novel silver(I) two-dimensional coordination polymer of thiophosphoric triamide ligand with two different coordination modes: Experimental, theoretical and molecular docking study

(Invited) Design, Synthesis and Applications of Two-Dimensional π-Conjugated Polymers

π-Electron conjugation in graphene gives rise to unusual electronic properties including massless charge carriers. In principle, some of these properties could be harvested in organic two-dimensional (2D) conjugated polymers which would open up the design space and tunability that are not available to inorganic 2D materials.[1] I will present our progress in synthesis of such structures as atomically thin layers on metallic surface,[2] and as bulk layered structures (2D Covalent Organic Frameworks),[3-5] via dynamic solution polymerization. I will discuss the structure-optoelectronic properties relationships in these materials and the perspectives for their applications in semiconducting devices.[1] DF Perepichka, F Rosei, Science 2009, 323, 216.[2] G Galeotti et al, Nat. Mater. 2020, 19, 874. D Dettmann et al, ACS Nano 2024, 18, 849.[3] T Jadhav et al, Angew. Chem. Int. Ed. 2019, 58, 13753. T Jadhav et al, J. Am. Chem. Soc. 2020, 142, 8862.[4] V Lakshmi et al. J. Am. Chem. Soc. 2020, 142, 2155. E Hamzehpoor et al., in preparation.[5] E Hamzehpoor et al. J. Am. Chem. Soc. 2021, 143, 13274. E Hamzehpoor et al. Nat. Chem. 2023, 15, 83.

(Invited) Mesoscale Ordered Two-Dimensional Semiconductor Polymers with Tunable Dirac Cones and Flat Bands

Dirac cones, present in the band structure of graphene, are responsible of its remarkable charge-transport properties. However, they are not exclusive to graphene but require that the material presents specific symmetry and delocalized electrons. Efforts have been devoted to identifying 2D materials beyond graphene that offer a greater degree of tunability and a non-zero band gap while retaining high carrier mobility [1].On-surface synthesis represents an opportunity to manipulate the electronic band structure of the material by varying the molecular building blocks (e.g. by the change of constituent atoms and symmetry). By using a class of heteroatom substituted triangulene monomers we synthesized mesoscale ordered 2D π-conjugated polymers on Au(111) with semiconducting properties arranged in a kagome lattice showing Dirac cone structures and flat bands, theoretically predicted [2-3]. We demonstrate that it is possible to tune the Dirac cone structures and flat bands energy positions by changing the bridging atoms in the triangulene monomers [4]. These results overcome the major barriers to the application of 2D π-conjugated polymers due small domain size and high defect density attained so far.Although the 2D polymers have been obtained on a metal surface, they can be detached and transferred to other substrates to be used in devices.

Topology of Gemini-shaped Hexagonal Heterojunction for Efficient Stereoconvergent Transformation via Dynamic Kinetic Resolution.

Despite recent advances in the combination of kinetic resolution and racemization for efficient stereoconvergent transformation, the poor stability and limited reaction activities of the products restrict their wide application in industrial production. To overcome these problems, Gemini-shaped hexagons with para-heterojunctions for one-dimensional and two-dimensional supramolecular polymers were designed via hydrogen-bonding adhesion by racemization catalyst 1 and kinetic resolution 2 in this work. The polymers from the assembly of Gemini-shaped hexagons exhibit rapid catalytic behaviour with efficient selectivity for the desired configuration in the synthesis of tertiary alcohols with contiguous stereocenters through dynamic kinetic resolution for the nanoscale heterojunctions of dissimilar catalysts. Among them, the developed 2D polymers gave outstanding enantioselectivities and diastereoselectivities (>99 % ee, 20 : 1 dr) through the cooperation of adjacent dissimilar catalysts. The heterojunctions varying dimensions and distances of dissimilar catalysts provide new insight for increasing the enantioselectivity of chiral organocatalysts.

Luminescent iron phthalocyanine organic polymer nanosheets with space-separated dual-active sites for the detection and photocatalytic reduction of Cr(Ⅵ) from wastewater

Cr(Ⅵ) residues in livestock and poultry wastewater are a rising concern for human health and biotic environments. For the removal of Cr(Ⅵ), its simultaneous reduction and adsorption represents a sustainable and efficient strategy. Herein, iron nodes on covalently bonded two-dimensional phthalocyanine organic polymer (PcOP-Fe) nanosheets with space-separated dual-active sites are developed for the simultaneous detection and removal of Cr(VI) from wastewater. In the FeN4 structure of PcOP-Fe nanosheets, Fe acts as an electron capture center, effectively facilitating the accumulation of photogenerated electrons and transferring them to Cr(VI), thereby achieving its photocatalytic reduction. Meanwhile, pyrrolic nitrogen provides excellent adsorption sites, enabling the adsorption of Cr(III) or Cr(0). Fe accumulates the photogenerated electrons from pyrrole N and transfer them to Cr(Ⅵ). The formation of N-Cr(Ⅲ) bonds causes a space-separation between Cr(Ⅵ) and Cr(III). In addition, PcOP-Fe can be used for a Cr(Ⅵ) detection agent. The photoluminescence intensity decreases linearly with increasing Cr(Ⅵ) concentration from 80 μM to 2 mM, with a limit of detection of 0.18 μM. The PcOP-Fe nanosheets exhibit good Cr(Ⅵ) detection and reduction performance in livestock and poultry wastewater, suggesting their suitability for practical sensing applications. Thus, the PcOP-Fe nanosheets with space-separated dual-active sites are promising for the simultaneous detection and removal of Cr(Ⅵ) in water treatment processes.

Synthesis and structure of a non-van-der-Waals two-dimensional coordination polymer with superconductivity

Two-dimensional conjugated coordination polymers exhibit remarkable charge transport properties, with copper-based benzenehexathiol (Cu-BHT) being a rare superconductor. However, the atomic structure of Cu-BHT has remained unresolved, hindering a deeper understanding of the superconductivity in such materials. Here, we show the synthesis of single crystals of Cu3BHT with high crystallinity, revealing a quasi-two-dimensional kagome structure with non-van der Waals interlayer Cu-S covalent bonds. These crystals exhibit intrinsic metallic behavior, with conductivity reaching 103 S/cm at 300 K and 104 S/cm at 2 K. Notably, superconductivity in Cu3BHT crystals is observed at 0.25 K, attributed to enhanced electron-electron interactions and electron-phonon coupling in the non-van der Waals structure. The discovery of this clear correlation between atomic-level crystal structure and electrical properties provides a crucial foundation for advancing superconductor coordination polymers, with potential to revolutionize future quantum devices.

Folding behaviors of two-dimensional flexible polymers.

Unlike one-dimensional polymers, the theoretical framework on the behaviors of two-dimensional (2D) polymers is far from completeness. In this study, we model single-layer flexible 2D polymers of different sizes and examine their scaling behaviors in solution, represented by Rg ∼ Lν, where Rg is the radius of gyration and L is the side length of a 2D polymer. We find that the scaling exponent ν is 0.96 for a good solvent and 0.64 for under poor solvent condition. Interestingly, we observe a previously unnoticed phenomenon: under intermediate solvent conditions, the 2D polymer folds to maintain a flat structure, and as L becomes larger, multiple folded structures emerge. We introduce a shape parameter Q to diagram the relationship of folded structures with the polymer size and solvent condition. Theoretically, we explain the folding transitions by the competition between bending and solvophobic free energies.

On the scaling of the osmotic pressure of two-dimensional polymers in the transition from the semidilute to the melt regimes

On the scaling of the osmotic pressure of two-dimensional polymers in the transition from the semidilute to the melt regimes

Fabrication of two novel two-dimensional copper-based coordination polymers regulated by the “V”-shaped second auxiliary ligands as high-efficiency urease inhibitors

Two novel copper-based coordination polymers (Cu-CPs) had been presented based on mixed ligands. The synthetic Cu-CP-1 and Cu-CP-2 were derived from a combination of two distinct forms of “V”-shaped bis-pyridine-bis-amide ligands and 1,2,4-benzenetricarboxylic acid (1,2,4-H3BTC). Distinct grid windows were seen in the simplified two-dimensional (2D) layers of the Cu-CPs due to the variable length of ligand regulation. These Cu-CPs had the potential to act as urease inhibitors (UIs), and the mechanisms responsible for their inhibition were extensively studied. The results indicated that both Cu-CPs exhibited significant urease inhibitory activities with urease inhibition rates of 88.02 % and 88.87 % at 100 µM and semi-inhibitory levels of IC50 of 0.92 ± 0.05 µM and 0.87 ± 0.03 µM, respectively. Furthermore, the inhibitory activities of the Cu-CPs were higher than those of the standard thiourea. An investigation of the enzyme kinetics of the Cu-CPs using Lineweaver–Burk (L–B) plots at various inhibitor doses demonstrated their non-competitive inhibitory nature, enhancing our comprehension of the possible mechanism by which these Cu-CPs exert urease inhibition. Furthermore, molecular docking was used to verify the interactions between Cu-CPs and the urease active site. The findings of the urease inhibition studies were good, and the impact of Cu-CP complexes on urease inhibition was examined using density functional theory (DFT) simulations.

Strategic Advancement in Inner Filter Effect Controllable Detection of Tetracyclines and Nitroaromatics in Real-World Matrices by Two-Dimensional Coordination Polymer

Strategic Advancement in Inner Filter Effect Controllable Detection of Tetracyclines and Nitroaromatics in Real-World Matrices by Two-Dimensional Coordination Polymer

Prediction of metal-free Stoner and Mott-Hubbard magnetism in triangulene-based two-dimensional polymers.

Ferromagnetism and antiferromagnetism require robust long-range magnetic ordering, which typically involves strongly interacting spins localized at transition metal atoms. However, in metal-free systems, the spin orbitals are largely delocalized, and weak coupling between the spins in the lattice hampers long-range ordering. Metal-free magnetism is of fundamental interest to physical sciences, unlocking unprecedented dimensions for strongly correlated materials and biocompatible magnets. Here, we present a strategy to achieve strong coupling between spin centers of planar radical monomers in π-conjugated two-dimensional (2D) polymers and rationally control the orderings. If the π-states in these triangulene-based 2D polymers are half-occupied, then we predict that they are antiferromagnetic Mott-Hubbard insulators. Incorporating a boron or nitrogen heteroatom per monomer results in Stoner ferromagnetism and half-metallicity, with the Fermi level located at spin-polarized Dirac points. An unprecedented antiferromagnetic half-semiconductor is observed in a binary boron-nitrogen-centered 2D polymer. Our findings pioneer Stoner and Mott-Hubbard magnetism emerging in the electronic π-system of crystalline-conjugated 2D polymers.

Highly Anion-Conductive Viologen-Based Two-Dimensional Polymer Membranes as Nanopower Generators.

Two-dimensional polymers (2DPs) and their layer-stacked 2D covalent organic frameworks (2D COFs) membranes hold great potential for harvesting sustainable osmotic energy. The nascent research has yet to simultaneously achieve high ionic flux and selectivity, primarily due to inefficient ion transport dynamics. This is directly related to ultrasmall pore size (<3 nm), much smaller than the duple Debye length in the diluted electrolyte (6-20 nm), as well as low charge density (<4.5 mC m-2). Here, we introduce a π-conjugated viologen-based 2DP (V2DP) membrane possessing a large pore size of 4.5 nm, strategically enhancing the overlapping of the electric double layer, coupled with an exceptional positive surface charge density (~6 mC m-2). These characteristics enable the membrane to facilitate high anion flux while maintaining ideal selectivity. Notably, V2DP membranes realize an impressive current density of 5.5×103 A m-2, surpassing benchmarks set by previously reported nanofluidic membranes. In the practical application scenario involving the mixing of artificial seawater and river water, the V2DP membranes exhibit a considerable ion transference number of 0.70 towards Cl-, contributing to an outstanding power density of ~55 W m-2. Theoretical calculations reveal the important role of the large quantity of anion transport sites, which act as binding sites evenly located in the positively charged N-containing pyridine rings. These binding sites enable kinematic coupling and decoupling between anions and the V2DP skeleton, establishing a continuous Cl- ion transport pathway. This work demonstrates the great promise of large-area ultrathin 2DP membranes featuring highly organized charged ion transport networks when applied for osmotic energy conversion.