Tunable Adhesion from Stoichiometry-Controlled and Sequence-Defined Supramolecular Polymers Emerges Hierarchically from Cyanostar-Stabilized Anion-Anion Linkages

Supramolecular polymerization and bulk properties relationship in ester-functionalized N-annulated perylenediimides

The synthesis of a series of N-annulated perylenediimides (NPDIs) 1-4 with an ester group and an alkyl spacer of different length in the peripheral chains was carried out, and the influence of the side chain architecture on the self-assembly, both in solution and in the solid state, was investigated. Solution studies evidenced that the carbonyl group plays a key role in the supramolecular organization of these derivatives, changing from an H-type isodesmic polymerization (4) to a J-type cooperative process as the spacer length decreases (1-3). On the other hand, bulk assays revealed an odd-even effect that correlates with the length of the alkyl spacer. Whereas the odd-spaced derivatives (2 and 4) organize in a disordered columnar hexagonal fashion, the even-spaced ones (1 and 3) show the formation of multiple crystalline (and liquid crystalline) structures. The results presented herein highlight the importance of side chain functionalization in the design of building blocks for in-solution and bulk purposes.

Small Ionic-Liquid-Based Molecule Drives Strong Adhesives

Nature has inspired scientists to fabricate adhesive materials for applications in many burgeoning areas. However, it is still a significant challenge to develop small-molecule adhesives with high-strength, low-temperature and recyclable properties, although these merits are of great interest in various aspects. Herein, we report a series of strong adhesives based on low-molecular-weight molecular solids driven by the terminal modification of ionic liquids (ILs) and subsequent supramolecular self-assembly. The emergence of high strength and liquid-to-solid transitions for these supramolecular aggregates relies on modifying IL with a high melting point motif and enriching the types of noncovalent interactions in the original ILs. Using this strategy, we demonstrate that our IL-based molecular solids can efficiently obtain a high adhesion strength (up to 8.95 MPa). Importantly, we elucidate the mechanism underlying the reversible and strong adhesion enabled by monomer-to-polymer transitions. These fundamental findings provide guidance for the design of high-performance supramolecular adhesive materials.

Electronically and geometrically complementary perylenediimides for kinetically controlled supramolecular copolymers

The synthesis of 3,4,9,10-benzo[d,e]isoquinolino[1,8-g,h]quinoline-tetracarboxylic diimide (BQQDI) 1 endowed with peripheral trialkoxybenzamide fragments is reported and its self-assembling features investigated. The peripheral benzamide moieties generate metastable monomeric species that afford a kinetically controlled supramolecular polymerization. The electron-withdrawing character of 1 in comparison with previously reported PDIs 2, together with the similar geometry, makes this dye an optimal candidate to perform seeded supramolecular copolymerization yielding four different supramolecular block copolymers. Whilst heteropolymers poly-1-co-2a, poly-2a-co-1 and poly-1-co-2b present an H-type arrangement of the monomeric units, heteropolymer poly-2b-co-1, prepared by seeding the chiral, metastable monomers of 2b with achiral seeds of 1, produces chiral, J-type aggregates. Interestingly, the monosignated CD signal of pristine poly-2b changes to a bisignated CD signal most probably due to the formation of columnar domains around the seeds of 1 which implies the blocky nature of the supramolecular copolymers formed.

Chemical Design of Supramolecular Reversible Adhesives for Promising Applications

Supramolecular reversible adhesives have garnered significant attention due to their potential applications in various fields. These adhesives exhibit remarkable properties such as reversible adhesion, self-healing, and high flexibility. This concept aims to present a comprehensive overview of the current research progress in developing supramolecular reversible adhesives. Firstly, the fundamentals of supramolecular chemistry and the principles underlying the design and synthesis of reversible adhesive systems are discussed. Next, the concept focuses on characterizing the reversible adhesion strength of supramolecular adhesive systems that have been developed. The adhesion performance of supramolecular reversible adhesives is summarized, highlighting their unique characteristics and promising applications. Finally, the challenges and future perspectives in the field of supramolecular reversible adhesives are discussed. The comprehensive overview provided in this concept aims to inspire further research and innovation in this exciting field.

Remote control of anion binding by CH-based receptors

We show that the substitution of tetra(benzimidazole)resorcin[4]arenes with electron withdrawing groups on the upper rim enhances anion binding at the opposite edge by more than three orders of magnitude. Moreover, selective anion binding at either the OH/NH or CH binding sites is demonstrated.

Electrolyte Modulation Strategies for Low-Temperature Zn Batteries

Aqueous rechargeable Zn metal batteries (ARZBs) are extensively studied recently because of their low-cost, high-safety, long lifespan, and other unique merits. However, the terrible ion conductivity and insufficient interfacial redox dynamics at low temperatures restrict their extended applications under harsh environments such as polar inspections, deep sea exploration, and daily use in cold regions. Electrolyte modulation is considered to be an effective way to achieve low-temperature operation for ARZBs. In this review, first, the fundamentals of the liquid-solid transition of water at low temperatures are revealed, and an in-depth understanding of the critical factors for inferior performance at low temperatures is given. Furthermore, the electrolyte modulation strategies are categorized into anion/concentration regulation, organic co-solvent/additive introduction, anti-freezing hydrogels construction, and eutectic mixture design strategies, and emphasize the recent progress of these strategies in low-temperature Zn batteries. Finally, promising design principles for better electrolytes are recommended and future research directions about high-performance ARZBs at low temperatures are provided.

A library of vinyl phosphonate anions dimerize with cyanostars, form supramolecular polymers and undergo statistical sorting

Supramolecular dimers are elementary units allowing the build-up of multi-molecule architectures. New among these are cyanostar-stabilized dimers of phosphate and phosphonate anions. While the anion dimerization at the heart of these assemblies is reliable, the covalent synthesis leading to this class of designer anions serves as a bottleneck in the pathway to supramolecular assemblies. Herein, we demonstrate the reliable synthesis of 14 diverse anionic monomers by Heck coupling between vinyl phosphonic acid and aryl bromide compounds. When this synthesis is combined with reliable anion dimerization, we show formation of supramolecular dimers and polymers by co-assembly with cyanostar macrocycles. The removal of the covalent bottleneck opened up a seamless synthetic route to iterate through three monomers affording the solubility needed to characterize the mechanism of supramolecular polymerization. We also test the idea that the small size of these vinyl phosphonates provide identical dimer stabilities across the library by showing how mixtures of anions undergo statistical (social) self-sorting. We exploit this property by preparing soluble copolymers from the mixing of different monomers. This multi-anion assembly shows the utility of a library for programming properties.

Chiral supramolecular polymers

As an active branch within the field of supramolecular polymers, chiral supramolecular polymers (SPs) are an excellent benchmark to generate helical structures that can clarify the origin of homochirality in Nature or help determine new exciting functionalities of organic materials. Herein, we highlight the most utilized strategies to build up chiral SPs by using chiral monomeric units or external stimuli. Selected examples of transfer of asymmetry, in which the point or axial chirality contained by the monomeric units is efficiently transferred to the supramolecular scaffold yielding enantioenriched helical structures, will be presented. The importance of the thermodynamics and kinetics associated with those processes is stressed, especially the influence that parameters such as the helix reversal and mismatch penalties exert on the achievement of amplification of asymmetry in co-assembled systems will also be considered. Remarkable examples of breaking symmetry, in which chiral supramolecular polymers can be attained from achiral self-assembling units by applying external stimuli like stirring, solvent or light, are highlighted. Finally, the specific and promising applications of chiral supramolecular polymers are presented with recent relevant examples.

Steric Control over the Threading of Pyrophosphonates with One or Two Cyanostar Macrocycles during Pseudorotaxane Formation

The supramolecular recognition of anions is increasingly harnessed to achieve the self-assembly of supramolecular architectures, ranging from cages and polymers to (pseudo)rotaxanes. The cyanostar (CS) macrocycle has previously been shown to form 2 : 1 complexes with organophosphate anions that can be turned into [3]rotaxanes by stoppering. Here we achieved steric control over the assembly of pseudorotaxanes comprising the cyanostar macrocycle and a thread that is based, for the first time, on organo-pyrophosphonates. Subtle differences in steric bulk on the threads allowed formation of either [3]pseudorotaxanes or [2]pseudorotaxanes. We demonstrate that the threading kinetics are governed by the steric demand of the organo-pyrophosphonates and in one case, slows down to the timescale of minutes. Calculations show that the dianions are sterically offset inside the macrocycles. Our findings broaden the scope of cyanostar-anion assemblies and may have relevance for the design of molecular machines whose directionality is a result of relatively slow slipping.

Orthogonal, modular anion-cation and cation-anion self-assembly using pre-programmed anion binding sites

Subcomponent self-assembly relies on cation coordination whereas the roles of anions often only emerge during the assembly process. When sites for anions are instead pre-programmed, they have the potential to be used as orthogonal elements to build up structure in a predictable and modular way. We explore this idea by combining cation (M⁺) and anion (X^-) binding sites together and show the orthogonal and modular build up of structure in a multi-ion assembly. Cation binding is based on a ligand (L) made by subcomponent metal-imine chemistry (M⁺ = Cu⁺, Au⁺) while the site for anion binding (X^- = BF₄ ^-, ClO₄ ^-) derives from the inner cavity of cyanostar (CS) macrocycles. The two sites are connected by imine condensation between a pyridyl-aldehyde and an aniline-modified cyanostar. The target assembly [LM-CS-X-CS-ML],⁺ generates two terminal metal complexation sites (LM and ML) with one central anion-bridging site (X) defined by cyanostar dimerization. We showcase modular assembly by isolating intermediates when the primary structure-directing ions are paired with weakly coordinating counter ions. Cation-directed (Cu⁺) or anion-bridged (BF₄ ^-) intermediates can be isolated along either cation-anion or anion-cation pathways. Different products can also be prepared in a modular way using Au⁺ and ClO₄ ^-. This is also the first use of gold(i) in subcomponent self-assembly. Pre-programmed cation and anion binding sites combine with judicious selection of spectator ions to provide modular noncovalent syntheses of multi-component architectures.

Exploiting valuable supramolecular materials from waste plastics

A new family of supramolecular materials is exploited from waste thermosets via a one-step retrosynthetic approach, which exhibits distinguished adhesion properties in dry/wet environments, good corrosion resistance and dynamic reversibility. This work opens up a wide design space for supramolecular materials with excellent performances and proposes a new strategy for efficient utilization of hybrid degraded products.

Stereomutation and chiroptical bias in the kinetically controlled supramolecular polymerization of cyano-luminogens

The synthesis of two pairs of enantiomeric cyano-luminogens 1 and 2, in which the central chromophore is a p-phenylene or a 2,5-dithienylbenzene moiety, respectively, is described and their supramolecular polymerization under kinetic and thermodynamic control investigated. Compounds 1 and 2 form supramolecular polymers by quadruple H-bonding arrays between the amide groups and the π-stacking of the central aromatic moieties. In addition, the peripheral benzamide units are able to form intramolecularly H-bonded pseudocycles that behave as metastable monomer M* thus affording kinetically and thermodynamically controlled aggregated species AggI and AggII. The chiroptical and emissive features of compounds 1 and 2 strongly depend on the aggregation state and the nature of the central aromatic unit. Compounds 1 exhibit a bisignated dichroic response of different intensity but with similar sign for both AggI1 and AggII1 species, which suggests the formation of helical aggregates. In fact, these helical supramolecular polymers can be visualized by AFM imaging. Furthermore, both AggI and AggII species formed by the self-assembly of compounds 1 show CPL (circularly polarized light) activity of opposite sign depending on the aggregation state. Thienyl-derivatives 2 display dissimilar chiroptical, morphological and emissive characteristics for the corresponding kinetically and thermodynamically controlled aggregated species AggI and AggII in comparison to those registered for compounds 1. Thus, a stereomutation phenomenon is observed in the AggI2 → AggII2 conversion. In addition, AggI2 is arranged into nanoparticles that evolve to helical aggregates to afford AggII2. The dissimilar chiroptical and morphological features of AggI2 and AggII2 are also appreciated in the emissive properties. Thus, whilst AggI2 experiences a clear AIE (aggregation induced emission) process and CPL activity, the thermodynamically controlled AggII2 undergoes an ACQ (aggregation caused quenching) process in which the CPL activity is cancelled.

Small-Molecule-based Supramolecular Plastics Mediated by Liquid-Liquid Phase Separation

Plastics are one of the most widely used polymeric materials. However, they are often undegradable and non-recyclable due to the very stable covalent bonds of macromolecules, causing environmental pollution and health problems. Here, we report that liquid-liquid phase separation (LLPS) could drive the formation of robust, stable, and sustainable plastics using small molecules. The LLPS process could sequester and concentrate solutes, strengthen the non-covalent association between molecules and produce a bulk material whose property was highly related to the encapsulated water amounts. It was a robust plastic with a remarkable Young's modulus of 139.5 MPa when the water content was low while became adhesive and could instantly self-heal with more absorbed water. Finally, responsiveness enabled the material to be highly recyclable. This work allowed us to understand the LLPS at the molecular level and demonstrated that LLPS is a promising approach to exploring eco-friendly supramolecular plastics that are potential substitutes for conventional polymers.

Design, Synthesis, and Evaluation of a Set of Carboxylic Acid and Phosphate Prodrugs Derived from HBV Capsid Protein Allosteric Modulator NVR 3-778

Hepatitis B virus (HBV) capsid protein (Cp) is necessary for viral replication and the maintenance of viral persistence, having become an attractive target of anti-HBV drugs. To improve the water solubility of HBV capsid protein allosteric modulator (CpAM) NVR 3-778, a series of novel carboxylic acid and phosphate prodrugs were designed and synthesized using a prodrug strategy. In vitro HBV replication assay showed that these prodrugs maintained favorable antiviral potency (EC50 = 0.28−0.42 µM), which was comparable to that of NVR 3-778 (EC50 = 0.38 µM). More importantly, the cytotoxicity of prodrug N8 (CC50 > 256 µM) was significantly reduced compared to NVR 3-778 (CC50 = 13.65 ± 0.21 µM). In addition, the water solubility of prodrug N6 was hundreds of times better than that of NVR 3-778 in three phosphate buffers with various pH levels (2.0, 7.0, 7.4). In addition, N6 demonstrated excellent plasma and blood stability in vitro and good pharmacokinetic properties in rats. Finally, the hemisuccinate prodrug N6 significantly improved the candidate drug NVR 3-778’s water solubility and increased metabolic stability while maintaining its antiviral efficacy.

Small-molecule ionic liquid-based adhesive with strong room-temperature adhesion promoted by electrostatic interaction

Low-molecular-weight adhesives (LMWAs) possess many unique features compared to polymer adhesives. However, fabricating LMWAs with adhesion strengths higher than those of polymeric materials is a significant challenge, mainly because of the relatively weak and unbalanced cohesion and interfacial adhesion. Herein, an ionic liquid (IL)-based adhesive with high adhesion strength is demonstrated by introducing an IL moiety into a Y-shaped molecule replete with hydrogen bonding (H-bonding) interactions. The IL moieties not only destroyed the rigid and ordered H-bonding networks, releasing more free groups to form hydrogen bonds (H-bonds) at the substrate/adhesive interface, but also provided electrostatic interactions that improved the cohesion energy. The synthesized IL-based adhesive, Tri-HT, could directly form thin coatings on various substrates, with high adhesion strengths of up to 12.20 MPa. Advanced adhesives with electrical conductivity, self-healing behavior, and electrically-controlled adhesion could also be fabricated by combining Tri-HT with carbon nanotubes.

Molecular Engineering of Noncovalent Dimerization

Dimers are probably the simplest model to facilitate the understanding of fundamental physical and chemical processes that take place in much-expanded systems like aggregates, crystals, and other solid states. The molecular interplay within a dimer differentiates it from the corresponding monomeric state and determines its features. Molecular engineering of noncovalent dimerization through applied supramolecular restrictions enables additional control over molecular interplay, particularly over its dynamic aspect. This Perspective introduces the recent effort that has been made in the molecular engineering of noncovalent dimerization, including supramolecular dimers, folda-dimers, and macrocyclic dimers. It showcases how the variation in supramolecular restrictions endows molecular-based materials with improved performance and/or functions like enhanced emission, room-temperature phosphorescence, and effective catalysis. We particularly discuss pseudostatic dimers that can sustain molecular interplay for a long period of time, yet are still flexible enough to adapt to variations. The pseudostatic feature allows for active species to decay along an alternate pathway, thereby spinning off emerging features that are not readily accessible from conventional dynamic systems.

Low-molecular-weight supramolecular adhesives based on non-covalent self-assembly of a small molecular gelator

Currently developed adhesives are overwhelmingly polymeric in nature. Herein, we highlight for the first time the potential of supramolecular eutectogels assembled from small molecules as robust low-molecular-weight (LMW) supramolecular adhesives in air, water and organic solvents, and under low temperatures. These supramolecular eutectogels were produced from commercial alkyl trimethyl ammonium bromide (C_nTAB) in emerging deep eutectic solvents (DESs), which demonstrated rapid (∼2 min), robust, and tunable adhesion to both hydrophilic and hydrophobic surfaces at room temperature in air. Moreover, high adhesion performance was maintained even in liquid nitrogen (-196 °C), underwater, and in organic solvents. A study of the structure-property relationship of these adhesives and molecular dynamics (MD) simulations further clarified the assembly and adhesion mechanism of the C₁₂TAB molecules in DESs. Compared with traditional polymer adhesives and several existing examples of LMW supramolecular adhesives with solvent-free dry network structures, the spontaneous self-assembly of LMW gelators in versatile DESs provides a new strategy for the facile construction of high-strength supramolecular adhesives with gel network structures for a diverse range of harsh environments.

Supramolecular Polymeric Pressure-Sensitive Adhesive That Can Be Directly Operated at Low Temperatures

Low-temperature adhesion is ubiquitous in daily life and industry. However, most supramolecular adhesives are thermoplastic materials that require heating during the adhesion. Herein, a supramolecular approach is used to construct unique pressure-sensitive adhesives (PSAs) that can be directly operated at low temperatures (-60 °C). Supramolecular polymerization between phytic acid (PA) and water (H) endows poly(PA-H)s with excellent mechanical properties and low temperature adhesion capacity. Poly(PA-H)s can easily be processed into PSA tapes, pastes, and particles. Poly(PA-H)s were directly adhered to various surfaces by pressing at low temperatures (0 to -60 °C). No heating or high-temperature-induced solid-liquid transition was required for the low-temperature adhesion of poly(PA-H)s. With the help of structural water units in supramolecular polymers, poly(PA-H)s showed strong, stable, and organic solvent resistant adhesion performances at low temperatures, with adhesion strength of up to 3.61 MPa at -60 °C.

A guanidino-γ-cyclodextrin superdimer generates a twin receptor for phosphate dimers assembled by anti-electrostatic hydrogen bonds

Octakis-6-guadinidino-γ-cyclodextrin (gguan) hydrochloride in the presence of phosphates crystallises from aqueous solution in the unprecedented form of a superdimer (dimer-within-a-dimer). The self-assembly exposes four circular octa-guanidinium regions that bind and stabilise discrete H-bonded phosphate anion dimers. The small (∼2 nm) gguan-phosphate assembly is preorganised and stable in aqueous solution, as demonstrated by DLS and NMR experiments.

Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics

Intermolecular bonding attraction at π-bonded centers is often described as "electrostatically driven" and given quasi-classical rationalization in terms of a "pi hole" depletion region in the electrostatic potential. However, we demonstrate here that such bonding attraction also occurs between closed-shell ions of like charge, thereby yielding locally stable complexes that sharply violate classical electrostatic expectations. Standard DFT and MP2 computational methods are employed to investigate complexation of simple pi-bonded diatomic anions (BO-, CN-) with simple atomic anions (H-, F-) or with one another. Such "anti-electrostatic" anion-anion attractions are shown to lead to robust metastable binding wells (ranging up to 20-30 kcal/mol at DFT level, or still deeper at dynamically correlated MP2 level) that are shielded by broad predissociation barriers (ranging up to 1.5 Å width) from long-range ionic dissociation. Like-charge attraction at pi-centers thereby provides additional evidence for the dominance of 3-center/4-electron (3c/4e) nD-π*AX interactions that are fully analogous to the nD-σ*AH interactions of H-bonding. Using standard keyword options of natural bond orbital (NBO) analysis, we demonstrate that both n-σ* (sigma hole) and n-π* (pi hole) interactions represent simple variants of the essential resonance-type donor-acceptor (Bürgi-Dunitz-type) attraction that apparently underlies all intermolecular association phenomena of chemical interest. We further demonstrate that "deletion" of such π*-based donor-acceptor interaction obliterates the characteristic Bürgi-Dunitz signatures of pi-hole interactions, thereby establishing the unique cause/effect relationship to short-range covalency ("charge transfer") rather than envisioned Coulombic properties of unperturbed monomers.

A cucurbit[8]uril-stabilized 3D charge transfer supramolecular polymer with a remarkable confinement effect for enhanced photocatalytic proton reduction and thioether oxidation

A water-soluble porous supramolecular polymer is assembled through a CB[8]-based 2 + 2 host–guest binding motif, which can greatly increase the efficiency of photocatalysis.

Precision synthesis of linear oligorotaxanes and polyrotaxanes achieving well-defined positions and numbers of cyclic components on the axle

Interest in macromolecules has increased because of their functional properties, which can be tuned using precise organic synthetic methods. For example, desired functions have been imparted by controlling the nanoscale structures of such macromolecules. In particular, compounds with interlocked structures, including rotaxanes, have attracted attention because of their unique supramolecular structures. In such supramolecular structures, the mobility and freedom of the macrocycles are restricted by an axle and dependent on those of other macrocycles, which imparts unique functions to these threaded structures. Recently, methods for the ultrafine engineering and synthesis, as well as functions, of "defined" rotaxane structures that are not statistically dispersed on the axle (i.e., control over the number and position of cyclic molecules) have been reported. Various synthetic strategies allow access to such well-defined linear oligo- and polyrotaxanes, including [1]rotaxanes and [n]rotaxanes (mostly n > 3). These state-of-the-art synthetic methods have resulted in unique functions of these oligo-and polyrotaxane materials. Herein, we review the effective synthetic protocols and functions of precisely constructed one-dimensional oligomers and polymers bearing defined threaded structures, and discuss the latest reports and trends.

Adhesion behaviour of bulk supramolecular polymers via pillar[5]arene-based molecular recognition

Pillar[n]arenes were rarely used as the building blocks for supramolecular adhesives. Herein, pillar[5]arene-based supramolecular polymer materials with tough adhesion behaviours on different substrates were prepared, with adhesion strengths up to 4.75 MPa. Strong and long-term dichloromethane-resistant adhesion performances were successfully obtained.

"Anti-electrostatic" Halogen Bonding between Ions of Like Charge

Halogen bonding occurs between molecules featuring Lewis acidic halogen substituents and Lewis bases. It is often rationalized as a predominantly electrostatic interaction and thus interactions between ions of like charge (e. g., of anionic halogen bond donors with halides) seem counter-intuitive. Herein, we provide an overview on such complexes. First, theoretical studies are described and their findings are compared. Next, experimental evidences are presented in the form of crystal structure database analyses, recent examples of strong "anti-electrostatic" halogen bonding in crystals, and the observation of such interactions also in solution. We then compare these complexes to select examples of "counter-intuitive" adducts formed by other interactions, like hydrogen bonding. Finally, we comment on key differences between charge-transfer and electrostatic polarization.

On-Site Supramolecular Adhesion to Wet and Soft Surfaces via Solvent Exchange

A series of poly(thioctic acid-catechol)s was prepared by supramolecular copolymerization of two low-molecular-weight monomers, thioctic acid (TA) and catechol (CA). The addition of a small amount of CA molecules significantly improved the adhesion ability of poly(TA) and transformed it into an applicable supramolecular polymer adhesive material. The robust adhesion of poly(TA-CA)s to soft surfaces was achieved by employing a hot-melt method. However, the supramolecular adhesion via the hot-melt method failed to perform in the presence of water. On-site supramolecular adhesion to wet and soft substrates was successfully realized through the solvent exchange behavior between water and the poly(TA-CA)s ethanol solution. Compared to the hot-melt method, the solvent exchange method displays various fascinating advantages and is suitable for adhesion conditions normally under the presence of water.

Poly(ionic liquid)s Containing Alkoxy Chains and Bis(trifluoromethanesulfonyl)imide Anions as Highly Adhesive Materials

Adhesive materials have wide applications in diverse fields, but the development of a novel and multipurpose adhesive is a great challenge. This study demonstrates that conventional poly(ionic liquid)s (PILs) can be designed as highly efficient adhesives by simply introducing alkoxy moieties into the cationic backbone of PILs containing bis(trifluoromethanesulfonimide) (TFSI^- ) anions. The incorporated flexible alkoxy chain not only reduces the glass transition temperature of PILs but also endows these materials with strong hydrogen bonding interactions, which, together with the unique electrostatic interaction of the PILs, simultaneously contributes to a high cohesive energy and interfacial adhesive energy. Consequently, these alkoxy PILs are highly adhesive on various substrates such as glass, ceramic, stainless steel, aluminum, and polymers, in contrast to the nonadhesive behavior of conventional PILs. Photosensitive or electronically conductive composite adhesives are fabricated by virtue of the compatibility between ionic liquids and carbon nanotubes or silver nanofibers. Interestingly, the PIL-2-TFSI adhesive possesses a unique and reversible response to electric fields and achieves up to 35% improvement in adhesive strength.

Iterative Exponential Growth of Oxygen-Linked Aromatic Polymers Driven by Nucleophilic Aromatic Substitution Reactions

This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (SNAr) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1H-1H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C-H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.

Anion mediated, tunable isoguanosine self-assemblies: decoding the conformation influence and solvent effects

Systematic investigations were performed with various substituted groups at C8 purine and ribose. A series of isoG analogs, C8-phenyl substituted isoG were synthesized and applied for Cs+ coordination. The structural proximity between purine and ribose limited pentaplex formation for C8-phenyl substituted isoG derivatives. Based on this observation, deoxy isoG derivative with modification on ribose (tert-butyldimethylsilyl ether) was applied to assemble with the Cs+ cation. Critical solvent (CDCl3 and CD3CN) and anion (BPh4 -, BARF-, and PF6 -) effects were revealed, leading to the controllable formation of various stable isoG pentaplexes, including singly charged decamer, doubly charged decamer, and 15-mer, etc. Finally, the X-ray crystal structure of [isoG20Cs3]3+(BARF-)3 was successfully obtained, which is the first example of multiple-layer deoxy isoG binding with the Cs+ cation, providing solid evidence of this new isoG ionophore beyond two-layer sandwich self-assembly.

"Texas-Sized" Molecular Boxes: From Chemistry to Applications

The design and synthesis of novel macrocyclic host molecules continues to attract attention because such species play important roles in supramolecular chemistry. However, the discovery of new classes of macrocycles presents a considerable challenge due to the need to embody by design effective molecular recognition features, as well as ideally the development of synthetic routes that permit further functionalization. In 2010, we reported a new class of macrocyclic hosts: a set of tetracationic imidazolium macrocycles, which we termed “Texas-sized” molecular boxes (TxSBs) in homage to Stoddart’s classic “blue box” (CBPQT⁴⁺). Compared with the rigid blue box, the first generation TxSB displayed considerably greater conformational flexibility and a relatively large central cavity, making it a good host for a variety of electron-rich guests. In this review, we provide a comprehensive summary of TxSB chemistry, detailing our recent progress in the area of anion-responsive supramolecular self-assembly and applications of the underlying chemistry to water purification, information storage, and controlled drug release. Our objective is to provide not only a review of the fundamental findings, but also to outline future research directions where TxSBs and their constructs may have a role to play.

Anion-Selective Electrodes Based On a CH-Hydrogen Bonding Bis-macrocyclic Ionophore with a Clamshell Architecture

CH-hydrogen bonding provides access to new building blocks for making macrocyclic ionophores with high degrees of preorganization and selective anion recognition. In this study, an anion-binding ionophore in the shape of a clamshell (ClS) was employed that is composed of two cyanostar (CNstar) macrocycles with preorganized cavities linked with a 12-carbon chain. This ionophore allows for anion complexation by CH-hydrogen bonding. The potentiometric performance of membrane-based ion-selective electrodes incorporating this ionophore was evaluated. Different membrane compositions were prepared to determine the optimum concentrations of the ionophore and lipophilic additive in the membrane. The optimized electrode had a slope of -58.2 mV/decade and demonstrated an anti-Hofmeister selectivity pattern toward iodide with a nanomolar detection limit. Electrospray ionization mass spectrometry was employed to study the relative association strengths of ClS with various anions. The observed mass peaks of the ion-ionophore complexes were found to be consistent with the potentiometric selectivity pattern of the corresponding electrodes. Overall, the selectivity of the electrode could be altered by using an ionophore in which the two CNstar macrocycles are linked together with a flexible 12-carbon chain to control the molecularity of the binding event.

Chain Entropy Beats Hydrogen Bonds to Unfold and Thread Dialcohol Phosphates inside Cyanostar Macrocycles To Form [3]Pseudorotaxanes

The recognition of substituted phosphates underpins many processes including DNA binding, enantioselective catalysis, and recently template-directed rotaxane synthesis. Beyond ATP and a few commercial substrates, however, little is known about how substituents effect organophosphate recognition. Here, we examined alcohol substituents and their impact on recognition by cyanostar macrocycles. The organophosphates were disubstituted by alcohols of various chain lengths, dipropanol, dihexanol, and didecanol phosphate, each accessed using modular solid-phases syntheses. Based on the known size-selective binding of phosphates by π-stacked dimers of cyanostars, threaded [3]pseudorotaxanes were anticipated. While seen with butyl substituents, pseudorotaxane formation was disrupted by competitive OH···O- hydrogen bonding between both terminal hydroxyls and the anionic phosphate unit. Crystallography also showed formation of a backfolded propanol conformation resulting in an 8-membered ring and a perched cyanostar assembly. Motivated by established entropic penalties accompanying ring formation, we reinstated [3]pseudorotaxanes by extending the size of the substituent to hexanol and decanol. Chain entropy overcomes the enthalpically favored OH···O- contacts to favor random-coil conformations required for seamless, high-fidelity threading of dihexanol and didecanol phosphates inside cyanostars. These studies highlight how chain length and functional groups on phosphate's substituents can be powerful design tools to regulate binding and control assembly formation during phosphate recognition.

Supramolecular Adhesion at Extremely Low Temperatures: A Combined Experimental and Theoretical Investigation

Adhesive materials that are resistant to low temperatures have wide applications in daily life, scientific research, and industry. Currently, the overwhelming majority of low-temperature-resistant adhesives are traditional polymer systems. In this study, a new strategy was developed to obtain strong and long-lasting adhesion effects from low-molecular-weight adhesives at low temperatures. The introduction of water molecules and the formation of hydrogen bonds not only triggered supramolecular polymerization but also endowed the water-involved copolymer with low-temperature resistance. The water content of the polymeric supramolecular system played a crucial role in exhibiting adhesion behavior at low temperatures. Good adhesion performance was obtained in extremely low-temperature environments, including liquid nitrogen.

Rational Design and Bulk Synthesis of Water-Containing Supramolecular Polymers

The utilization of structural water in chemical self-assembly has not only effectively eliminated the negative influences of solvents from solutions or gels but has also provided new insight into the fabrication of new materials in bulk. However, up to now, supramolecular polymerization triggered by structural water has been dominated more by serendipity than rational design. After carefully analyzing the chemical structures of artificial monomers and gaining a deep understanding of the water-triggered assembly process, we report herein the bulk formation of polymeric materials from water and low-molecular weight monomers by rational design instead of serendipity.

Recognition and applications of anion-anion dimers based on anti-electrostatic hydrogen bonds (AEHBs)

Based on Coulomb's Law alone, electrostatic repulsion between two anions is expected to prevent their dimerization. Contrary to that idea, this Tutorial Review will present evidence showing that anion-anion dimers of protic hydroxyanions can form readily, and describe conditions that facilitate their formation. From X-ray crystal structures, we learn that hydroxyanions dimerize and oligomerize by overcoming long-range electrostatic opposition. Common examples are hydroxyanions of phosphate, sulfate, and carbonate, often in partnership with charged and neutral receptors. Short-range hydrogen bonds between anionic donors and acceptors are defined as anti-electrostatic hydrogen bonds (AEHBs) with insight from theoretical studies. While anion dimers are difficult to identify unequivocally in solution, these solution dimers have recently been definitively identified. The development of the supramolecular chemistry of anion-anion dimers has led to applications in hierarchical assemblies, such as supramolecular polymers and hydrogen bonded organic frameworks.

Formation of self-assembled supramolecular polymers by anti-electrostatic anion-anion and halogen bonding interactions

We report here the formation of self-assembled supramolecular polymers in which the cooperative action of anti-electrostatic anion-anion and halogen-bonding interactions serve as a powerful driving force for the formation of large supramolecular polymers. DOSY-NMR, DLS, TEM, SEM and X-ray experiments provide evidence of the formation of supramolecular structures in solution and solid state.