Engineering Functionalization in a Supramolecular Polymer: Hierarchical Self-Organization of Triply Orthogonal Non-covalent Interactions on a Supramolecular Coordination Complex Platform

Thermal-Sensitive Supramolecular Coordination Complex Formed by Orthogonal Metal Coordination and Host-Guest Interactions for an Electrical Thermometer

Supramolecular coordination complexes (SCCs) are popular for their structural diversity and functional adaptability, which make them suitable for a wide range of applications. Photophysical and mechanical performance of SCCs are the most attractive characteristics, yet their ionically conductive behavior and potential in electrical sensing have been rarely investigated. This study reports a well-designed SCC that integrates orthogonal metal coordination and host-guest interactions to achieve sensitive electrical thermal sensing. Owing to the thermodynamic nature of the host-guest interaction, the SCC encounters thermally induced disassembly, leading to significantly enhanced ion mobility and thus allowing for the precise detection of minor temperature variation. The SCC-based thermometer is then fabricated with the assistance of 3D printing and demonstrates good accuracy and reliability in monitoring human skin temperature and real-time temperature changes of mouse during the whole anesthesia and recovery process. Our findings provide an innovative strategy for developing electrical thermometers and expand the current application scope of SCCs in electrical sensing.

Multiple non-covalent-interaction-directed supramolecular double helices: the orthogonality of hydrogen, halogen and chalcogen bonding

In this study, a benzoselenadiazole- and pyridine-bifunctionalized hydrogen-bonded arylamide foldamer was synthesized. A co-crystallization experiment with 1,4-diiodotetrafluorobenzene showed that a new type of supramolecular double helices, which were induced by three orthogonal interactions, namely, three-center hydrogen bonding (O⋯H⋯O), I⋯N halogen bonding and Se⋯N chalcogen bonding, have been constructed in the solid state. This work presents a novel instance of multiple non-covalent interactions that work together to construct supramolecular architectures.

Nested non-covalent interactions expand the functions of supramolecular polymer networks

Supramolecular polymer networks contain non-covalent cross-links that enable access to broadly tunable mechanical properties and stimuli-responsive behaviors; the incorporation of multiple unique non-covalent cross-links within such materials further expands their mechanical responses and functionality. To date, however, the design of such materials has been accomplished through discrete combinations of distinct interaction types in series, limiting materials design logic. Here we introduce the concept of leveraging "nested" supramolecular crosslinks, wherein two distinct types of non-covalent interactions exist in parallel, to control bulk material functions. To demonstrate this concept, we use polymer-linked Pd2L4 metal-organic cage (polyMOC) gels that form hollow metal-organic cage junctions through metal-ligand coordination and can exhibit well-defined host-guest binding within their cavity. In these "nested" supramolecular network junctions, the thermodynamics of host-guest interactions within the junctions affect the metal-ligand interactions that form those junctions, ultimately translating to substantial guest-dependent changes in bulk material properties that could not be achieved in traditional supramolecular networks with multiple interactions in series.

Photo-responsive metal-organic gels of rigid phenylene-1,3-di-substituted angular dienes with metal halides: gel-to-gel transformations triggered by [2 + 2] polymerization

Herein, the first report on gel-to-gel transformations via [2 + 2] photopolymerization in MOGs of metal halides and rigid dienes is presented. The MOGs and their xerogels show exceptional ability to undergo [2 + 2] polymerisation upon UV irradiation. Gel-to-gel transformations are very rare as the post-modification of gelators weakens the gel and transforms it to a sol. Such transformations change the molecular assemblies into gels with altered mechanical and chemical properties. These phenomena pave the way to synthesize new MOGs with improved rigidity that cannot be synthesized otherwise.

Recent advances in combatting bacterial infections via well-designed metallacycles/metallacages

Bacterial infections can lead to the development of large-scale outbreaks of diseases that pose a serious threat to human life and health. Also, conventional antibiotics are prone to producing resistance and allergic reactions, and their therapeutic effect is dramatically diminished when bacterial communities form biofilms. Fortunately, well-designed supramolecular coordination complexes (SCCs) have been used as antibacterials or anti-biofilms in recent years. SCCs can kill bacteria by directly engaging with the bacterial surface through electrostatic interactions or by penetrating the bacterial membrane through the auxiliary effect of cell-penetrating peptides. Furthermore, scientists have engineered fluorescent SCCs that can produce reactive oxygen species (ROS) to eliminate bacteria when exposed to laser irradiation, and they also demonstrate outstanding performance in in vivo imaging, enabling integrated diagnosis and treatment. In this review, we summarize the design strategy and applications of SCCs in antibacterials or anti-biofilms and provide an outlook on future research.

Enhancing the Toughness and Strength of Polymers Using Mechanically Interlocked Hydrogen Bonds

The energy dissipative features of hydrogen bonds under conditions of mechanical strain have provided an ongoing incentive to explore hydrogen bonding units for the purpose of controlling and customizing the mechanical properties of polymeric materials. However, there remains a need for hydrogen bond units that (1) possess directionality, (2) provide selectivity, (3) dissipate energy effectively, and (4) can be incorporated readily into polymeric materials to regulate their mechanical properties. Here, we report mechanically interlocked hydrogen bond units that incorporate multiple hydrogen bonds within a [2]catenane structure. The conformational flexibility and associated spatial folding characteristics of the [2]catenane units allow for molecular scale motion under external stress, while the interlocked structure serves as a pivot that maintains the directionality and selectivity of the resultant hydrogen bonding units. When incorporated into polymers, these interlocked hydrogen bond motifs serve to strengthen and toughen the resulting materials. This study not only presents a novel hydrogen bond unit for creating polymeric materials with improved mechanical properties but also underscores the unique opportunities that mechanically interlocked hydrogen bond structures may provide across a diverse range of applications.

Fluorophore-based host-guest assembly complexes for imaging and therapy

Recently, supramolecular chemistry with its unique properties has received considerable attention in many fields. Supramolecular fluorescent systems constructed on the basis of macrocyclic hosts are not only effective in overcoming the limitations of imaging and diagnostic reagents, but also in enhancing their performances. This paper summarizes the recent advances in supramolecular fluorescent systems based on host-guest interactions and their application in bioimaging and therapy as well as the challenges and prospects in developing novel supramolecular fluorescent systems.

Automated and Efficient Generation of General Molecular Aggregate Structures

Modeling intermolecular interactions of complex non-covalent structures is important in many areas of chemistry. To facilitate the generation of reasonable dimer, oligomer, and general aggregate geometries, we introduce an automated computational interaction site screening (aISS) workflow. This easy-to-use tool combines a genetic algorithm employing the intermolecular force-field xTB-IFF for initial search steps with the general force-field GFN-FF and the semi-empirical GFN2-xTB method for geometry optimizations. Compared with the alternative CREST program, aISS yields similar results but with computer time savings of 1-3 orders of magnitude. This allows for the treatment of systems with thousands of atoms composed of elements up to radon, e.g., metal-organic complexes, or even polyhedra and zeolite cut-outs which were not accessible before. Moreover, aISS can identify reactive sites and provides options like site-directed (user-guided) screening.

Graphene/Polymer Nanocomposites: Preparation, Mechanical Properties, and Application

Although polymers are very important and vastly used materials, their physical properties are limited. Therefore, they are reinforced with fillers to relieve diverse restrictions and expand their application areas. The exceptional properties of graphene make it an interesting material with huge potential for application in various industries and devices. The interfacial interaction between graphene and the polymer matrix improved the uniform graphene dispersion in the polymer matrix, enhancing the general nanocomposite performance. Therefore, graphene functionalization is essential to enhance the interfacial interaction, maintain excellent properties, and obstruct graphene agglomeration. Many studies have reported that graphene/polymer nanocomposites have exceptional properties that enable diverse applications. The use of graphene/polymer nanocomposites is expected to increase sustainably and to transform from a basic to an advanced material to offer optimum solutions to industry and consumers.

Metallacycle-cored fluorescent supramolecular polymer networks for the detection of acidic environments

Despite the challenges, supramolecular polymers (SPs) have received significant attention. In this study, pH-responsive fluorescent SPs were prepared by a bottom-up strategy. The rhombohedral metallacycle-cored supramolecular coordination complex (SCC) was first prepared by metal-ligand coordination between the 120° pyridinedione boron difluoride and the 60° crown ether-based platinum, which then interacted with ammonium salt-containing covalent polymers to form SP networks. These networks can potentially be used for the detection of organic acid solutions and inorganic acid vapours.

Output Enhancement of Triboelectric Nanogenerators Based on Hierarchically Regular Cadmium Coordination Polymers for Photocycloaddition

Exploiting the well-arranged and tunable frameworks of crystalline materials, we herein report coordination polymers (CPs) with modulated hierarchical structures as triboelectric materials to construct and extend the application scope of triboelectric nanogenerators (TENGs). Different lengths and shapes of bridging ligands [4,4'-bpa = 1,2-bis(4-pyridyl)ethane, 4,4'-bpe = 1,2-bis(4-pyridyl)ethene, and 4,4'-bpp = 1,3-di(2-pyridyl)propane for 1, 2, and 3, respectively] were used to construct Cd-CP-based hierarchical frameworks. These compounds were used as triboelectric materials, and their electronic structure contributions were determined by the output of the corresponding TENGs. The results indicated that 2-TENG with the 4,4'-bpe ligand had the highest output, attributed to the improvement in the electron activity due to the π-conjugation group in the bridging ligand, which was further verified by density functional theory calculations. Furthermore, 2@PVDF (PVDF = polyvinylidene fluoride) composite films with different concentrations of Cd-CP were prepared. Detailed electrical characterizations revealed that the arrangement of 12% active constituents of Cd-CP-2 effectively enhanced the output performance of 2@PVDF-TENG, which could light up an ultraviolet lamp plate to successfully execute the [2 + 2] photocycloaddition.

Self-assembled Pt(II) metallacycles enable precise cancer combination chemotherapy

Coadministration of drug molecules in adequate combinations for cancer treatment reduces the doses of each constituent, overcomes resistance mechanisms, and reduces the influence of tumor heterogeneity. Here we utilize coordination-driven self-assembly to prepare platinum(II) metallacycles comprising two drug molecules with distinct anticancer mechanisms in precise ratios. Nanoformulations fabricated by encapsulating the metallacycles into amphiphilic diblock copolymers efficiently enter cancer cells and release the active drug molecules at the exact loading ratio in the reductive cancer microenvironments, leading to a synergistic anticancer effect and therefore a favorable treatment outcome. This study provides a promising supramolecular methodology for the precise organization and delivery of bioactive molecules for inducing synergistic biological effects that maximize therapeutic efficacy.

Combination chemotherapy, which involves the simultaneous use of multiple anticancer drugs in adequate combinations to disrupt multiple mechanisms associated with tumor growth, has shown advantages in enhanced therapeutic efficacy and lower systemic toxicity relative to monotherapy. Herein, we employed coordination-driven self-assembly to construct discrete Pt(II) metallacycles as monodisperse, modular platforms for combining camptothecin and combretastatin A4, two chemotherapy agents with a disparate mechanism of action, in precise arrangements for combination chemotherapy. Formulation of the drug-loaded metallacycles with folic acid–functionalized amphiphilic diblock copolymers furnished nanoparticles with good solubility and stability in physiological conditions. Folic acids on the surface of the nanoparticles promote their internalization into cancer cells. The intracellular reductive environment of cancer cells induces the release of the drug molecules at an exact 1:1 ratio, leading to a synergistic anticancer efficacy. In vivo studies on tumor-bearing mice demonstrated the favorable therapeutic outcome and minimal side effects of the combination chemotherapy approach based on a self-assembled metallacycle.

Crown Ether-Based Supramolecular Polymers: From Synthesis to Self-Assembly

Supramolecular polymers not only possess many advantages of traditional polymers, but also have many unique characteristics. Supramolecular polymers can be constructed by self-assembly of various noncovalent interactions. Host-guest interaction, as one important type of noncovalent interactions, has been widely applied to construct supramolecular polymers. From the perspective of classification of the recognition system motifs, host-guest recognition motifs mainly include crown ether, cyclodextrin, calixarene, cucurbituril, and pillararene-based host-guest recognition pairs. Crown ethers, as the first-generation macrocyclic hosts, have played a very important part in the development of supramolecular chemistry. Due to the easy modification of crown ethers, various crown ether derivatives have been prepared by attaching some functional groups to the edges of crown ethers, which endowed them with some interesting properties and made them ideal candidates for the fabrication of supramolecular polymers. This review gives a review of the preparation of crown ether-based supramolecular polymers (CSPs) and summarizes crown ether-based recognition pairs, organization methods, topological structures, stimuli-responsiveness, and functional characteristics.

Self-Healing Metallacycle-Cored Supramolecular Polymers Based on a Metal-Salen Complex Constructed by Orthogonal Metal Coordination and Host-Guest Interaction with Amino Acid Sensing

A platinum(II) metallacycle-cored supramolecular network based on a metal-salen complex was successfully constructed by two orthogonal noncovalent interactions (host-guest interactions and metal coordination interactions). The obtained metallo-supramolecular polymer could further form gels when the concentration of metallacycle 1 was 160.0 mM. This gel exhibited multiple stimuli-responsive gel-sol phase transitions under different stimuli, such as temperature, competitive guests, etc. Moreover, it exhibited good self-healing properties and could be used as a turn-off sensor for thiol-containing amino acids.

Pillar[5]-bis-trithiacrown: Influence of Host-Guest Interactions on the Formation of Coordination Networks

A pillar[5]-bis-trithiacrown (L) capable of metal binding and organic guest threading simultaneously has been employed, and the influence of dinitrile guests [CN(CH₂)_nCN (n = 2-6: abbreviated C2-C6)] on the coordination behaviors has been investigated. When the ditopic ligand L was reacted with HgCl₂ in the presence of the C2-C6 guests, the shorter guests C2 and C3 afforded a two-dimensional coordination polymer [Hg₇Cl₁₄(C2@L)₂]_n (1) and a one-dimensional coordination polymer [(Hg₃Cl₆)₂(C3@L)₂]_n (2), respectively. In 1 and 2, each dinitrile guest threads into the pillararene cavity to form a C2@L or C3@L unit via the host-guest interaction. Further linking of these units by exocyclic Hg-S bonds and anion coordination lead to the formation of coordination products with different dimensionalities. While the use of the longer guests C4-C6 under the same reactions yielded a discrete dimercury(II) complex 3, [Hg₂Cl₄(CH₃CN@L)] which contains one acetonitrile solvent molecule because the longer dinitriles do not serve as effective guests. In the NMR and UV-vis studies, the association constants (log K_1:1) for the host-guest interactions of L with the dinitrile guests are C2 (4.75) > C3 (4.17) ≫ C4 (2.85) > C5 (2.45) > C6 (too small), indicating that the shorter guests C2 or C3 interact more strongly than longer ones due to the confined interior space of L. Taken collectively, the C2 and C3 guests with proper size-matching promote the formation of coordination polymers and vice versa, suggesting that the guest size could be a controlling factor.

Stimuli-responsive polymer-based systems for diagnostic applications

Stimuli-responsive polymers exhibit properties that make them ideal candidates for biosensing and molecular diagnostics. Through rational design of polymer composition combined with new polymer functionalization and synthetic strategies, polymers with myriad responsivities, e.g., responses to temperature, pH, biomolecules, CO2, light, and electricity can be achieved. When these polymers are specifically designed to respond to biomarkers, stimuli-responsive devices/probes, capable of recognizing and transducing analyte signals, can be used to diagnose and treat disease. In this review, we highlight recent state-of-the-art examples of stimuli-responsive polymer-based systems for biosensing and bioimaging.

Nanosheets and Hydrogels Formed by 2 nm Metal-Organic Cages with Electrostatic Interaction

We report the mechanism of hydrogel formation in dilute aqueous solutions (>15 mg/mL) by 2 nm metal-organic cages (MOCs). Experiments and all-atom simulations confirm that with the addition of small electrolytes, the MOCs self-assemble into 2D nanosheets via counterion-mediated attraction because of their unique molecular structure and charge distribution as well as σ-π interactions. The stiff nanosheets are difficult to bend into 3-D hollow, spherical blackberry type structures, as observed in many other macroion systems. Instead, they stay in solution and their very large excluded volumes lead to gelation at low (∼1.5 wt %) MOC concentrations, with additional help from hydrophobic and partial π-π interactions similar to the gelation of graphene oxides.

Photochemical [2 + 2] polymerization of metal-organic gels of a rigid and angular diene with silver-salts of diverse anions: selective dye-sorption and luminescence by xerogels

Two similar types of dienes, one rigid and the other flexible, were explored for their gel formation abilities with Ag(i) salts. The rigid and angular dienes have shown an exceptional ability for gel formation with silver salts of nitrate, triflate, tetrafluoro borate and hexafluorophosphate. These metal-organic gels (MOGs) and their xerogels are found to have an excellent ability to undergo the photochemical [2 + 2] polymerization reaction upon irradiation. The reactions were monitored, and the products were characterized via1H NMR and MALDI-TOF analyses. Further, the solid-state luminescence behaviour and the selective dye-sorption of the gels have been explored before and after the photo-polymerization reaction.

Fluorescent Supramolecular Polymers Formed by Crown Ether-Based Host-Guest Interaction

Inspired by the vast array of assemblies present in nature, supramolecular chemistry has attracted significant attention on account of its diverse supra-structures, which include micelles, vesicles, and fibers, in addition to its extensive applications in luminescent materials, sensors, bioimaging, and drug delivery over the past decades. Supramolecular polymers, which represent a combination of supramolecular chemistry and polymer science, are constructed by non-covalent interactions, such as host-guest interactions, hydrogen bonding, hydrophobic or hydrophilic interactions, metal-ligand interactions, π-π stacking, and electrostatic interactions. To date, numerous host-guest recognition systems have been reported, including crown ethers, cyclodextrins, calixarenes, cucurbituril, pillararenes, and other macrocyclic hosts. Among them, crown ethers, as the first generation of macrocyclic hosts, provide a promising and facile alternative route to supramolecular polymers. In addition, the incorporation of fluorophores into supramolecular polymers could endow them with multiple properties and functions, thereby presenting potential advantages in the context of smart materials. Thus, this review focuses on the fabrication strategies, interesting properties, and potential applications of fluorescent supramolecular polymers based on crown ethers. Typical examples are presented and discussed in terms of three different types of building blocks, namely covalently bonded low-molecular-weight compounds, polymers modified by hosts or guests, and supramolecular coordination complexes.

Recent developments in the construction and applications of platinum-based metallacycles and metallacages via coordination

Coordination-driven suprastructures have attracted much interest due to their unique properties. Among these structures, platinum-based architectures have been broadly studied due to their facile preparation. The resultant two- or three-dimensional (2D or 3D) systems have many advantages over their precursors, such as improved emission tuning, sensitivity as sensors, and capture and release of guests, and they have been applied in biomedical diagnosis as well as in catalysis. Herein, we review the recent results related to platinum-based coordination-driven self-assembly (CDSA), and the text is organized to emphasizes both the synthesis of new metallacycles and metallacages and their various applications.

A Self-Cross-Linking Supramolecular Polymer Network Enabled by Crown-Ether-Based Molecular Recognition

Supramolecular polymers based on host-guest molecular recognition have emerged as promising platforms for the development of smart materials. However, the studies on them are primarily conducted in solution and/or in the gel state. In contrast, little is known about dynamic properties and applications of supramolecular polymers in bulk. Herein, we present a self-cross-linking supramolecular polymer network (SPN) as a model system to understand the bulk properties controlled by noncovalent interactions. Specifically, the SPN monomer is composed of two benzo-21-crown-7 (B21C7) host units and two dialkylammonium salt guest moieties on a four-arm core, wherein complementary host-guest complexation drives the formation of the SPN with [2]pseudorotaxane linkages between B21C7 and ammonium motifs. The dynamic and reversible behaviors of the linkages are evaluated by measurement of viscoelasticity. The results indicate that the host-guest molecular recognition becomes highly dynamic at elevated temperature. Moreover, the relatively high activation energy of the SPN manifests itself as a new type of thermoplastic material with network topology freezing glass transition. Finally, we demonstrate how these findings provide insights into the malleability and processability of the SPN by simple demos. The fundamental understanding gained from the research on this SPN in bulk will facilitate the advancement and application of supramolecular materials.

Morphology transformation of pillararene-based supramolecular nanostructures

In this feature article, the construction methods and the factors that influence the morphological transformation of pillararene-based supramolecular nanostructures are reviewed.

Engineering orthogonality in the construction of an alternating rhomboidal copolymer with high fidelity via integrative self-sorting

An alternating rhomboidal copolymer was prepared through the combination of orthogonal self-assembly between metal-coordination and host-guest chemistry as well as integrative self-sorting strategy associated with molecular size and steric effect.

Self-Healing Heterometallic Supramolecular Polymers Constructed by Hierarchical Assembly of Triply Orthogonal Interactions with Tunable Photophysical Properties

Here, we present a method for the building of new bicyclic heterometallic cross-linked supramolecular polymers by hierarchical unification of three types of orthogonal noncovalent interactions, including platinum(II)-pyridine coordination-driven self-assembly, zinc-terpyridine complex, and host-guest interactions. The platinum-pyridine coordination provides the primary driving force to form discrete rhomboidal metallacycles. The assembly does not interfere with the zinc-terpyridine complexes, which link the discrete metallacycles into linear supramolecular polymers, and the conjugation length is extended upon the formation of the zinc-terpyridine complexes, which red-shifts the absorption and emission spectra. Finally, host-guest interactions via bis-ammonium salt binding to the benzo-21-crown-7 (B21C7) groups on the platinum acceptors afford the cross-linked supramolecular polymers. By continuous increase of the concentration of the supramolecular polymer to a relatively high level, supramolecular polymer gel is obtained, which exhibits self-healing properties and reversible gel-sol transitions stimulated by various external stimuli, including temperature, K⁺, and cyclen. Moreover, the photophysical properties of the supramolecular polymers could be effectively tuned by varying the substituents of the precursor ligands.

Topological Characterization of Coordination-Driven Self-assembly Complexes: Applications of Ion Mobility-Mass Spectrometry

Coordination-driven self-assembly (CDSA) is increasingly used to synthesize coordination complexes containing metal-centered electron acceptors and typically nitrogen-containing electron donors. Characterization of the structures obtained from CDSA via crystallographic or spectroscopic means is limited due to difficulties in forming single crystals for X-ray studies and overlapping precursor and product signals in NMR. Here, we employ ion mobility-mass spectrometry (IM-MS), which provides a direct measure of size and shape of the CDSA complexes, to study the intact reaction products of a rhomboid-shaped complex. This approach negates the need for product isolation and crystallization and allows for tracking of the product distribution as a function of time. A potential challenge of IM-MS is that the size/shape of the observed CDSA complexes can vary with internal energy; however, we show that proper tuning of the instrument reduces the effects of collisional activation thereby allowing for retention of ion conformations that reflect solution-phase ion structures. Graphical Abstract.

Endo- and Exo-Functionalized Tetraphenylethylene M12L24 Nanospheres: Fluorescence Emission inside a Confined Space

The intrinsic relationship between the properties of green fluorescent protein (GFP) and its encapsulated small molecular light machine has spurred many biomimicking studies, aiming at revealing the detailed mechanism and further promoting its wide applications in different disciplines. However, how to build a similar confined microenvironment to mimic the cavity of a β-barrel and the fluorescence turn-on process is a fundamental challenge for both chemists and biologists. Herein, two distinct exo- and endo-functionalized tetraphenylethylene (TPE)-based M12L24 nanospheres with precise distribution of anchored TPE moieties and unique photophysical properties were constructed by means of a coordination-driven self-assembly strategy. Under dilute conditions, the nanospheres fluoresce more strongly than the corresponding TPE subcomponents. Meanwhile, the endo-functionalized sphere is able to induce a higher local concentration and more restrained motion of the enclosed 24 TPE units compared with exo-functionalized counterpart and thus induces much stronger emission due to the restriction of the rotation of the pendant TPE units. The biomimetic methodology developed here represents a promising way to understand and construct artificial GFP materials on the platforms of supramolecular coordination complexes.

Spontaneous Formation of a Cross-Linked Supramolecular Polymer Both in the Solid State and in Solution, Driven by Platinum(II) Metallacycle-Based Host-Guest Interactions

The recent progress in platinum(II) coordination-driven supramolecular polymers has had a substantial effect on the design of functional soft materials. However, the prospect of realizing polymerization induced by platinum(II) metallacycle-based host-guest interactions has received little attention until recently. Here we report the realization of supramolecular polymerization driven by platinum(II) metallacycle-based host-guest interactions both in the solid state and in solution. On the basis of the disclosed polymerization mechanism, we present a new strategy for the preparation of platinum(II) metallacycle-based supramolecular polymers.

Soft Materials with Diverse Suprastructures via the Self-Assembly of Metal-Organic Complexes

Inspired by assemblies in the natural world, researchers have prepared diverse suprastructures with distinct spatial arrangements by artificial self-assembly, including micelles, vesicles, ribbons, films, fibers, and tubes. The field of assembly is undergoing a transition from single-component to multicomponent assembly and single-step to multistep processing. Control over the size, shape, and composition of these building blocks has enabled the formation of suprastructures with substantial structural diversity. More importantly, harnessing noncovalent interactions to create suprastructures in a controlled manner will lead to a better understanding of the formation of complex self-organized patterns. However, for the construction of multiscale self-assemblies with controllable shapes and functions, the selection of a suitable protocol remains challenging. Coordination-driven self-assembly provides a bottom-up approach to construct various metal-organic complexes (MOCs), which could be further used as building blocks with controllable shapes and sizes. Despite the tremendous progress made in the design of MOC-based supramolecular materials, most of these MOCs have dimensions of only several nanometers, and investigations of these structures rely on the characterization of their crystal structure. However, most of the functional suprastructures in living organisms have dimensions ranging from microns to centimeters and have the form of soft materials. Thus, obtaining MOC-based highly ordered materials of larger size remains a challenge. This Account focuses on our recent advances in the construction of soft suprastructure materials with MOCs. A series of functionalized MOCs was first constructed through coordination-driven self-assembly. Then, further self-assembly of the as-prepared MOCs gave rise to the formation of higher-order structures. By changing the functional groups in the acceptors and donors in the MOCs, different suprastructures, including nanospheres, nanodiamonds, nanorods, nanofibers, membranes, films, and gels, were prepared. These studies suggest that using MOCs as building blocks is a highly efficient strategy to achieve complex architectures and functional materials for the development of desired MOC-based soft materials with high precision and fidelity.

Formation of an interlocked double-chain from an organic-inorganic [2]rotaxane

Here we show that a structure containing a polymeric interlocking daisy chain is obtained from the reaction of an inorganic-organic [2]rotaxane [HB{CrIII7NiII(μ-F)8(O2CtBu)16}], where B is an organic thread terminated with a bi-pyridyl unit, with an oxo-centered metal carboxylate triangle [FeIII2CoII(μ3-O)(O2CtBu)6(HO2CtBu)3].

Ring-opening supramolecular polymerization controlled by orthogonal non-covalent interactions

The π–π interaction has been successfully utilized to orthogonally regulate the supramolecular polymerization driven by quadruple hydrogen bonding.

A ureido-pyrimidone based aspartic acid derivative: synthesis and pH-responsive self-assembly in water

The pH-responsive UPy-aspartic acid aggregates can act as templates for the controlled synthesis of silver nanostructures.

Recent developments in the construction of metallacycle/metallacage-cored supramolecular polymers via hierarchical self-assembly

Supramolecular polymers have received considerable attention during the last few decades due to their scientific value in polymer chemistry and profound implications for future developments of advanced materials. Discrete supramolecular coordination complexes (SCCs) with well-defined size, shape, and geometry have been widely employed to construct hierarchical systems by coordination-driven self-assembly with the spontaneous formation of metal-ligand bonds, which results in the formation of well-defined two-dimensional (2D) metallacycles or three-dimensional (3D) metallacages with high functionalities. The incorporation of discrete SCCs into supramolecular polymers by the orthogonal combination of metal-ligand coordination and other noncovalent interactions or covalent bonding could further facilitate the construction of novel supramolecular polymers with hierarchical architectures and multiple functions including controllable uptake and release of guest molecules, providing a flexible platform for the development of smart materials. In this review, the recent progress in metallacycle/metallacage-cored supramolecular polymers that were constructed by the combination of metal-ligand interactions and other orthogonal interactions (including hydrophobic or hydrophilic interactions, hydrogen bonding, van der Waals forces, π-π stacking, electrostatic interactions, host-guest interactions and covalent bonding) has been discussed. In addition, the potential applications of metallacycle/metallacage-cored supramolecular polymers in the areas of light emitting, sensing, bio-imaging, delivery and release, etc., are also presented.

Microphase separation of a quadruple hydrogen bonding supramolecular polymer: effect of the steric hindrance of the ureido-pyrimidone on their viscoelasticity

Supramolecular polymers based on 2-ureido-4[1H]-pyrimidone (UPy) units with extremely high dimerization constants and adjustable properties have received significant attention. In this work, we attempt to discuss the relationship between the micro-phase separation and the viscoelastic properties of the supramolecular polymers. For this reason, polymers with different UPy moieties structures and different UPy moieties contents were prepared and studied. It was found that the UPy moiety with little hindrance at the six-position of the pyrimidone could self-assemble into a nano-fiber structure and the degree of the micro-phase separation increased with the content of the UPy moiety. With the enlargement of the steric hindrance of the six-position of the pyrimidone, the nano-fiber structure gradually disappeared, meaning the degree of the micro-phase separation decreased astonishingly. More importantly, with the degree of the micro-phase separation increased, the storage modulus or the elasticity modulus increased exponentially and the T_m and the loss modulus area increased linearly. These results would lead a new way to study and develop novel polymeric materials.

The supramolecular polymers based on 2-ureido-4[1H]-pyrimidone (UPy) with different structure were prepared and the effects of microtopography on the viscoelasticity were investigated.

Metallacycle-Cored Supramolecular Polymers: Fluorescence Tuning by Variation of Substituents

Herein, we present a method for the preparation of supramolecular polymers with tunable fluorescence via the combination of metal-ligand coordination and phenanthrene-21-crown-7 (P21C7)-based host-guest interactions. A suite of rhomboidal metallacycles with different substituents were prepared via the coordination-driven self-assembly of a P21C7-based 60° diplatinum(II) acceptor and 120° dipyridyl donors. Upon variation of the substituents on the dipyridyl donors, the metallacycles exhibit emission wavelengths spanning the visible region (λmax = 427-593 nm). Metallacycle-cored supramolecular polymers were obtained via host-guest interactions between bis-ammonium salts and P21C7. The supramolecular polymers exhibit emission wavelengths similar to those of the individual metallacycles and higher fluorescent efficiency in solution and thin films. Utilizing a yellow-emitting supramolecular polymer thin film with high quantum yield (0.22), a white-light-emitting LED was fabricated by painting the thin film onto an ultraviolet LED. This study presents an efficient approach for tuning the properties of fluorescent supramolecular polymers and the potential of the metallacycle-cored supramolecular polymers as a platform for the fabrication of light-emitting materials with good processability and tunability.

Assembly of Metallacages into Soft Suprastructures with Dimensions of up to Micrometers and the Formation of Composite Materials

This work provides a platform for the rapid generation of superstructure assemblies with a wide range of lengths that can be used to access a variety of metal-organic complex-based soft superstructures. Metallacage-based microneedles that are nanometers in diameter and millimeters in length were generated in dichloromethane and ethyl acetate; their size could be controlled by adjusting the ratio of the two solvents. Interestingly, microflower structures could be formed by further assembly of the microneedles during solvent evaporation. Our study establishes a feasible method designed to broaden the range of suprastructures with emissions from blue and green to red through the co-assembly of lysine-modified perylene. Similar to the co-assembly of lysine-modified perylene with microflowers, chlorophyll-a and vitamin B₁₂ were introduced into the microflowers during the assembly process, which may be exploited in studies of energy capture and nerve repair in the future.

Preparation of cross-linked supramolecular polymers based on benzo-21-crown-7/secondary ammonium salt host-guest interactions

We found that TC7 not only self-assembles into one-dimensional supramolecular aggregates in chloroform, but also forms cross-linked supramolecular polymers via host-guest complexation between benzo-21-crown-7 and secondary ammonium salts. Compared with one-dimensional linear supramolecular polymers, soft and long viscous fibers were pulled out from a concentrated solution of cross-linked supramolecular polymers as a result of higher viscosity and lower diffusion coefficients.