A Highly Efficient Supramolecular Polymer-Based Singlet Oxygen Generator for Photocatalytic Minisci Alkylation

Supramolecular polymers, with their specific functional units and structures, can effectively enhance the absorption and utilization of light energy, thereby facilitating more efficient photocatalytic organic reactions. In the present work, we constructed a supramolecular polymer consisting of benzothiazole derivatives (BTBP) and cucurbit[8]uril (CB[8]). The BTBP monomer, known for its unique chemical structure and properties, has been found to exhibit a remarkable capability in generating singlet oxygen (1O2). As a result of the constraining impact of the macrocyclic molecule, the inclusion of CB[8] resulted in an effective enhancement in the ability to generate 1O2 while forming supramolecular polymer BTBP-CB[8]. When evaluating the quantum yield of 1O2 using Rose Bengal (RB) as a reference photosensitizer (75% in water), BTBP-CB[8] demonstrated an enhanced 1O2 quantum yield compared to BTBP, with an impressive yield of 152.4%, demonstrating that the formation of supramolecular polymer contributes to its ability to generate 1O2. Subsequently, BTBP-CB[8], a highly efficient 1O2 generator, was employed for the photocatalytic Minisci alkylation reaction, resulting in an impressive reaction yield of up to 89%. The supramolecular polymer strategies employed in the construction of photocatalytic systems have exhibited remarkable efficacy in the production of 1O2, underscoring their immense prospects in photocatalysis.

Triterpene-Based Prodrug for Self-Boosted Drug Release and Targeted Oral Squamous Cell Carcinoma Chemotherapy

Chemotherapy is one of the main treatments for oral squamous cell carcinoma (OSCC), especially as a combined modality approach with and after surgery or radiotherapy. Limited therapeutic efficiency and serious side effects greatly restrict the clinical performance of chemotherapeutic drugs. The development of smart nanomedicines has provided new research directions, to some extent. However, the involvement of complex carrier compositions inevitably brings biosafety concerns and greatly limits the "bench-to-bed" translation of most nanomedicines reported. In this study, a carrier-free self-assembled prodrug was fabricated by two triterpenes (glycyrrhetinic acid, GA and ginsenoside Rh2, Rh2) isolated from medicinal plants, licorice, and ginseng, for the targeted and highly effective treatment of OSCC. Reactive oxygen species (ROS) self-supplied molecule TK-GA2 was synthesized with ROS-responsive thioketal linker and prodrug was prepared by a rapid-solvent-exchange method with TK-GA2 and Rh2. After administration, oral tumor cells transported large amounts of prodrugs with glucose ligands competitively. Endogenous ROS in oral tumor cells then promoted the release of GA and Rh2. GA further evoked the generation of a large number of ROS to help self-boosted drug release and increase oxidative stress, synergistically causing tumor cell apoptosis with Rh2. Overall, this carrier-free triterpene-based prodrug might provide a preeminent opinion on the design of effective chemotherapeutics with low systemic toxicity against OSCC.

Stimuli-Responsive Molecular Duplexes Displaying Duplex-to-Duplex Switching

Synthetic duplexes with high stabilities have promising potential for mimicking biomolecular functions and developing supramolecular smart materials. Herein, we describe the synthesis and stimuli-responsive properties of molecular duplexes derived from indolocarbazole-pyridine (I-P) oligomers. These duplexes adopt nonclassical helical structures, stabilized by I-P hydrogen-bonding pairs in anhydrous chlorinated solvents. Notably, the longest duplex 62 (11-mer)2 displays remarkable stability, forming twenty hydrogen bonds; its exchange energy barrier was determined to be ΔG≠=22.0 kcal ⋅ mol-1 at 75 °C in anhydrous (CDCl2)2. Upon the addition of water, a hydrated duplex 62 (11-mer)2⊃10H2O was formed, with one water molecule inserted between each I-P hydrogen-bonding pair. The Hill coefficient (n) for this process is 6.1, demonstrating extremely positive cooperativity. Conversely, the hydrated duplex 62 (11-mer)2⊃10H2O was completely converted into the original anhydrous duplex 62 (11-mer)2 when the temperature was increased. Interconversion between these two distinct duplexes can be repeatedly carried out by varying the temperature. Furthermore, reversible switching between hetero-duplexes and homo-duplexes was also demonstrated by controlling the temperature, with concomitant changes in the characteristic emission signals.

Structural Landscape of α-Acetamidocinnamic Acid Cocrystals with Bipyridine-Based Coformers: Influence of Crystal Packing on Their Thermal and Photophysical Properties

Controlling the supramolecular synthon outcome in systems with different functionalities has been a key factor for the design of supramolecular materials, which also affected their physicochemical properties. In this contribution, we have analyzed the structural landscape of α-acetamidocinnamic acid (HACA) aiming to find its synthon outcome from the competitivity between its acidic and amidic groups. We prepared four multicomponent forms including one dihydrate (HACA·2H2O) and three cocrystals bearing different bipyridine coformers with formulas (HACA)2(1,2-bpe) (1), (HACA)2(4,4'-azpy) (2), and (HACA)2(4,4'-bipy)3 (3) (1,2-bpe = 1,2-bis(4-pyridyl)ethylene; 4,4'-azpy = 4,4'-azopyridine; 4,4'-bipy = 4,4'-bipyridine). First, we applied a virtual screening approach to assess the feasibility of cocrystal formation. Then, we synthesized the cocrystals, via liquid-assisted grinding (LAG) (1 and 2) or solvothermal (3) techniques, and single crystals of HACA, and their four multicomponent forms were obtained showing different synthons and crystal packings. Besides, a Cambridge Structural Database (CSD) search of the cocrystals presenting bipyridine-type coformers and molecules with acid and amide functionalities was performed, and the observed synthon occurrences as well as the possibility of synthon modification by tuning the H-donor/H-acceptor propensity of the acidic and amidic groups were shown. Finally, we measured their thermal and photophysical properties, which were correlated with their structural features.

Interfacial Preparation of Polyoxometalate-Based Hybrid Supramolecular Polymers by Orthogonal Self-Assembly

The construction of organic-inorganic hybrid supramolecular polymers using polyoxometalate (POM) as building block is expected to bring new opportunities to the functionalization of supramolecular polymers and the development of novel POM-based soft materials. Here, by using the orthogonal self-assembly based on host-guest interactions and metal-ligand interactions, we report the in situ construction of a novel POM-based hybrid supramolecular polymer (POM-SP) at the oil-water interface, while the redox and competitive responsiveness can be triggered independently. Moreover, the binding energy of POM-SP at the interface is sufficiently strong so that the assembly of POM-SP jams, allowing the stabilization of liquids in nonequilibrium shapes, offering the possibility of fabricating all-liquid constructs with reconfigurability.

Solution-based Supramolecular Hierarchical Assembly of Frenkel Excitonic Nanotubes Driven by Gold Nanoparticle Formation and Temperature

Translating nature's successful design principle of solution-based supramolecular self-assembling to broad applications─ranging from renewable energy and information technology to nanomedicine─requires a fundamental understanding of supramolecular hierarchical assembly. Though the forces behind self-assembly (e.g., hydrophobicity) are known, the specific mechanism by which monomers form the hierarchical assembly still remains an open question. A crucial step toward formulating a complete mechanism is understanding not only how the monomer's specific molecular structure but also how manifold environmental conditions impact the self-assembling process. Here, we elucidate the complex correlation between the environmental self-assembling conditions and the resulting structural properties by utilizing a well-characterized model system: well-defined supramolecular Frenkel excitonic nanotubes (NTs), self-assembled from cyanine dye molecules in aqueous solution, which further self-assemble into bundled nanotubes (b-NTs). The NTs and b-NTs inhabit distinct spectroscopic signatures, which allows the use of steady-state absorption spectroscopy to monitor the transition from NTs to b-NTs directly. Specifically, we investigate the impact of temperature (ranging from 23 °C, 55 °C, 70 °C, 85 °C, up to 100 °C) during in situ formation of gold nanoparticles to determine their role in the formation of b-NTs. The considered time regime for the self-assembling process ranges from 1 min to 8 days. With our work, we contribute to a basic understanding of how environmental conditions impact solution-based hierarchical supramolecular self-assembly in both the thermodynamic and the kinetic regime.

Arylazopyrazole as a photo-switch for controllable self-assembly of pillar[6]arene-based supramolecular amphiphiles

A photo-responsive host-guest molecular recognition between a cationic pillar[6]arene host and an arylazopyrazole derived guest was established. Based on this novel recognition motif, a photo-controllable supra-amphiphile was constructed. The spontaneous aggregation can be reversibly controlled by irradiation with UV (365 nm) and green light (520 nm), leading to a switch between spherical nanoparticles and vesicle-like aggregates.

Supramolecular Soft Material Enabled by Metal Coordination and Hydrogen Bonding: Stretchability, Self-Healing, Impact Resistance, 3D Printing, and Motion Monitoring

Metal coordination can significantly improve the macroscopic performance of many materials by enhancing their dynamic features. In this study, two supramolecular interactions, Fe³⁺ -carboxylic acid coordination, and structural water-induced hydrogen bonding, into an artificial polymer were introduced. Various attractive features, including flexibility and stretchability, are achieved because of the bulk state and dynamic hydrogen bonds of poly(thioctic acid-water) (poly[TA-H]). These unique features are considerably enhanced after the incorporation of Fe³⁺ cations into poly[TA-H] because metal coordination increased the mobility of the poly[TA-H] chains. Thus, the poly(thioctic acid-water-metal) (poly[TA-HM]) copolymer exhibited better flexibility and stretchability. Moreover, notable underwater/low-temperature self-healing capacity is obtained via the synergistic effect of the metal and hydrogen bonding. Most of the impact energy is quickly absorbed by poly[TA-H] or poly[TA-HM] and effectively and rapidly dissipated via reversible debonding/bonding via the interactions between the metal and hydrogen. Macroscopic plastic deformation or structural failure is not observed during high-speed (50-70 m s^-1 ) impact experiments or high-altitude (90 m) falling tests. Furthermore, poly[TA-HM] displayed good thermal molding properties, which enabled its processing via 3D fused deposition modeling printing. Poly[TA-HM] also showed considerable effectiveness for monitoring complicated, dynamic, and irregular biological activities owing to its highly pressure-sensitive nature.

Pillararene-Based Supramolecular Polymers for Cancer Therapy

Supramolecular polymers have attracted considerable interest due to their intriguing features and functions. The dynamic reversibility of noncovalent interactions endows supramolecular polymers with tunable physicochemical properties, self-healing, and externally stimulated responses. Among them, pillararene-based supramolecular polymers show great potential for biomedical applications due to their fascinating host-guest interactions and easy modification. Herein, we summarize the state of the art of pillararene-based supramolecular polymers for cancer therapy and illustrate its developmental trend and future perspective.

Multistep sequence-controlled supramolecular polymerization by the combination of multiple self-assembly motifs

The precise sequence control of polymer chain is an important research topic of polymer chemistry. Although some methods such as iterative synthesis and supramolecular polymerization have been developed to fabricate sequence-controllable polymer, it is still a great challenge to consecutively prepare multiple supramolecular polymers with different sequence structures. In this work, through the reasonable utilization of assembly motifs, we integrated multiple host-guest recognitions and metal coordination interactions to prepare different sequence-controlled supramolecular polymers by a multistep assembly strategy. This research provides inspiration for the design and preparation of supramolecular polymers with different sequence structures.

J-aggregation strategy of organic dyes for near-infrared bioimaging and fluorescent image-guided phototherapy

With the continuous development of organic materials for optoelectronic devices and biological applications, J-aggregation has attracted a great deal of interest in both dye chemistry and supramolecular chemistry. Except for the characteristic red-shifted absorption and emission, such ordered head-to-tail stacked structures may be accompanied by special properties such as enhanced absorption, narrowed spectral bandwidth, improved photothermal and photodynamic properties, aggregation-induced emission enhancement (AIEE) phenomenon, and so forth. These excellent properties add great potential to J-aggregates for optical imaging and phototherapy in the near-infrared (NIR) region. Despite decades of development, the challenge of rationally designing the molecular structure to adjust intermolecular forces to induce J-aggregation of organic dyes remains significant. In this review, we discuss the formation of J-aggregates in terms of intermolecular interactions and summarize some recent studies on J-aggregation dyes for NIR imaging and phototherapy, to provide a clear direction and reference for designing J-aggregates of near-infrared organic dyes to better enable biological applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

A Supramolecular Hydrogel Based on Copolymers of Acrylic Acid and Maleic Anhydride Derivatives with Terpyridine Motifs

A kind of terpyridine derivative (NH₂-Tpy) in which the amino was incorporated by a short alkyl chain was synthesized. Through grafting of terpyridine units into the hydrophilic copolymers of maleic anhydride and acrylic acid PAAMa via the reaction of the amino groups in NH₂-Tpy and the maleic anhydride units, a series of gelator polymers—P1, P2, and P3—containing different contents of terpyridine units was synthesized. Under coordination of Ni²⁺ and terpyridine ligands in linear polymers, the supramolecular hydrogels H1, H2, and H3 with different cross-linking degrees were prepared. The linear polymers P1–P3 had a strong absorption peak at about 290 nm in the UV-vis spectra which was attributed to π–π* transition, and there was a new peak at about 335 nm led by the metal-to-ligands charge transfer (MLCT) when coordinated with Ni²⁺ ions. According to the rheological behaviors, the storage modulus (G′) was larger than the loss modulus (G′′). These hydrogels showed typical gel-like characteristics when the terpyridine content of the hydrogels exceeded 10%, and the hydrogels showed liquid-like characteristics when the terpyridine content of the hydrogels was less than 7%. The results of the micromorphological investigation of the xerogels from SEM illustrated the metal–terpyridine coordination cross-linking could have an important influence on the microstructures of the resulting hydrogels. Furthermore, these hydrogels based on supramolecular cross-links exhibited reversible solution–gel transition at different environmental temperatures. At the same time, the equilibrium swelling of the supramolecular hydrogels was 8.0–12.3 g/g, which increased with the decrease in the content of the terpyridine units in the resulting hydrogels.

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.

Visualizing molecular weights differences in supramolecular polymers

Molecular weight determinations play a vital role in the characterization of supramolecular polymers. They are essential to assessing the degree of polymerization, which in turn can have a significant impact on the properties of the polymer. While numerous characterization methods have been developed to estimate the number-average molecular weight (M_n) of supramolecular polymers, a simple visual method could provide advantages in terms of ease of use. We have now developed a system wherein differences in the fluorescent signature, including changes in color, allow variations in the M_n of an anion-responsive supramolecular polymer [M1·Zn(OTf)₂]_n to be readily monitored. The present visual differentiation strategy provides a tool that may be used to characterize supramolecular polymers.

Issues of molecular weight determination have been central to the development of supramolecular polymer chemistry. Whereas relationships between concentration and optical features are established for well-behaved absorptive and emissive species, for most supramolecular polymeric systems no simple correlation exists between optical performance and number-average molecular weight (M_n). As such, the M_n of supramolecular polymers have to be inferred from various measurements. Herein, we report an anion-responsive supramolecular polymer [M1·Zn(OTf)₂]_n that exhibits monotonic changes in the fluorescence color as a function of M_n. Based on theoretical estimates, the calculated average degree of polymerization (DP_cal) increases from 16.9 to 84.5 as the monomer concentration increases from 0.08 mM to 2.00 mM. Meanwhile, the fluorescent colors of M1 + Zn(OTf)₂ solutions were found to pass from green to yellow and to orange, corresponding to a red shift in the maximum emission band (λ_max). Therefore, a relationship between DP_cal and λ_max could be established. Additionally, the anion-responsive nature of the present system meant that the extent of supramolecular polymerization could be regulated by introducing anions, with the resulting change in M_n being readily monitored via changes in the fluorescent emission features.

Janus Cross-links in Supramolecular Networks

Thermosets composed of cross-linked polymers demonstrate enhanced thermal, solvent, chemical, and dimensional stability as compared to their non-cross-linked counterparts. However, these often-desirable material properties typically come at the expense of reprocessability, recyclability, and healability. One solution to this challenge comes from the construction of polymers that are reversibly cross-linked. We relied on lessons from Nature to present supramolecular polymer networks comprised of cooperative Janus-faced hydrogen bonded cross-links. A triazine-based guanine-cytosine base (GCB) with two complementary faces capable of self-assembly through three hydrogen bonding sites was incorporated into poly(butyl acrylate) to create a reprocessable and recyclable network. Rheological experiments and dynamic mechanical analysis (DMA) were employed to investigate the flow behavior of copolymers with randomly distributed GCB units of varying incorporation. Our studies revealed that the cooperativity of multiple hydrogen bonding faces yields excellent network integrity evidenced by a rubbery plateau that spanned the widest temperature range yet reported for any supramolecular network. To verify that each Janus-faced motif engages in multiple cross-links, we studied the effects of local concentration of the incorporated GCB units within the polymer chain. Mechanical strength improved by colocalizing the GCB within a block copolymer morphology. This enhanced performance revealed that the number of effective cross-links in the network increased with the local concentration of hydrogen bonding units. Overall, this study demonstrates that cooperative noncovalent interactions introduced through Janus-faced hydrogen bonding moieties confers excellent network stability and predictable viscoelastic flow behavior in supramolecular networks.

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.

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.

3D Printing of Solvent-Free Supramolecular Polymers

Additive manufacturing has significantly changed polymer science and technology by engineering complex material shapes and compositions. With the advent of dynamic properties in polymeric materials as a fundamental principle to achieve, e.g., self-healing properties, the use of supramolecular chemistry as a tool for molecular ordering has become important. By adjusting molecular nanoscopic (supramolecular) bonds in polymers, rheological properties, immanent for 3D printing, can be adjusted, resulting in shape persistence and improved printing. We here review recent progress in the 3D printing of supramolecular polymers, with a focus on fused deposition modelling (FDM) to overcome some of its limitations still being present up to date and open perspectives for their application.

Modulating the Photophysical Properties and Electron Transfer Rates in Diketopyrrolopyrrole-Based Coordination Polymers

Molecular self-assembly through noncovalent interactions is a particularly efficient approach to fine-tune the optoelectronic and photophysical properties of electroactive materials. In metal-ligand coordination polymers, the final properties of the assemblies are directly related to the nature of the metal-ligand interaction. To probe for such influence on the photophysical properties of electroactive materials, a series of coordination polymers based on a well-known organic dye, diketopyrrolopyrrole, was prepared through coordination of a terpyridine-containing monomer with various metal sources, including iron, cobalt, zinc, and manganese. The resulting supramolecular polymers were characterized through multiple techniques, including UV-vis and fluorescence spectroscopy, time-correlated single-photon counting, and femtosecond transient absorption spectroscopy to reveal the impact of the metal source on the final photophysical properties of coordination polymers. As expected, important variations were found between different coordination polymers in terms of absorption, fluorescence kinetics, and electron transfer rate. While iron and cobalt-containing polymers showed ultrafast electrons transfer rates, assemblies from manganese were shown to be much less efficient, confirming the importance of metal centers. This detailed fundamental study unravels some important relationships between metal-ligand interactions, supramolecular self-assembly, and photophysical properties, ultimately leading to new avenues for the design of functional polymers based on organic dyes.

Hierarchical self-assembly and controlled disassembly of a cavitand-based host–guest supramolecular polymer

Two hierarchical aggregation modes of cavitand-based supramolecular polymers allow implementing orthogonal disassembly procedures: electrochemical reduction for linear chains and solvent-driven dissolution for bundles.

Correlation between Locally Ordered (Hydrogen-Bonded) Nanodomains and Puzzling Dynamics of Polymethysiloxane Derivative

We examined the behavior of poly(mercaptopropyl)methylsiloxane (PMMS), characterized by a polymer chain backbone of alternate silicon and oxygen atoms substituted by a polar pendant group able to form hydrogen bonds (-SH moiety), by means of infrared (FTIR) and dielectric (BDS) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and rheology. We observed that the examined PMMS forms relatively efficient hydrogen bonds leading to the association of chains in the form of ordered lamellar-like hydrogen-bonded nanodomains. Moreover, the recorded mechanical and dielectric spectra revealed the presence of two relaxation processes. A direct comparison of collected data and relaxation times extracted from two experimental techniques, BDS and rheology, indicates that they monitor different types of the mobility of PMMS macromolecules. Our mechanical measurements revealed the presence of Rouse modes connected to the chain dynamics (slow process) and segmental relaxation (a faster process), whereas in the dielectric loss spectra we observed two relaxation processes related most likely to either the association-dissociation phenomenon within lamellar-like self-assemblies or the sub-Rouse mode (α'-slower process) and segmental (α-faster process) dynamics. Data presented herein allow a better understanding of the peculiar dynamical properties of polysiloxanes and associating polymers having strongly polar pendant moieties.

Supramolecular Polymers With AIE Property Fabricated From a Cyanostilbene Motif-Derived Ditopic Benzo-21-Crown-7 and a Ditopic Dialkylammonium Salt

Fluorescent supramolecular polymers (FSP) have attracted considerable attention in recent years. Particularly, the incorporation of aggregation-induced emission (AIE) property to the FSP will bring this material into practical applications. Herein, we designed and synthesized a cyanostilbene motif derived ditopic benzo-21-crown-7 (B21C7) as a host molecule (H). The cyanostilbene motif endows H with AIE property while the B21C7 motif renders it with the capability to complex with electron deficient guest molecules. Upon the addition of a ditopic dialkylammonium salt molecule (G), a novel FSP with blue luminescent property can be constructed. This B21C7-based host-guest FSP with blue fluorescence may have potential application in supramolecular luminescent materials.

pH-Responsive Host-Guest Complexations Between a Water-Soluble Pillar[6]arene Dodecyl-Ammonium Chloride and Aromatic Sulfonic Acids

In the present work, new host-guest binding motifs based on a water-soluble pillar[6]arene dodecyl-ammonium chloride (CP6) with two aromatic sulfonic acids in aqueous media were fabricated. In accordance with the integrated results of ¹H NMR, 2D NOESY, and florescence titration experiments, it was demonstrated that the host-guest binding of CP6 with the two aromatic sulfonic acids in aqueous solution not only has high binding constants but also has pH-responsiveness.

100th Anniversary of Macromolecular Science Viewpoint: Engineering Supramolecular Materials for Responsive Applications-Design and Functionality

Supramolecular polymers allow access to dynamic materials, where noncovalent interactions can be used to offer both enhanced material toughness and stimuli-responsiveness. The versatility of self-assembly has enabled these supramolecular motifs to be incorporated into a wide array of glassy and elastomeric materials; moreover, the interaction of these noncovalent motifs with their environment has shown to be a convenient platform for controlling material properties. In this Viewpoint, supramolecular polymers are examined through their self-assembly chemistries, approaches that can be used to control their self-assembly (e.g., covalent cross-links, nanofillers, etc.), and how the strategic application of supramolecular polymers can be used as a platform for designing the next generation of smart materials. This Viewpoint provides an overview of the aspects that have garnered interest in supramolecular polymer chemistry, while also highlighting challenges faced and innovations developed by researchers in the field.

Macromolecular Engineering by Applying Concurrent Reactions with ATRP

Modern polymeric material design often involves precise tailoring of molecular/supramolecular structures which is also called macromolecular engineering. The available tools for molecular structure tailoring are controlled/living polymerization methods, click chemistry, supramolecular polymerization, self-assembly, among others. When polymeric materials with complex molecular architectures are targeted, it usually takes several steps of reactions to obtain the aimed product. Concurrent polymerization methods, i.e., two or more reaction mechanisms, steps, or procedures take place simultaneously instead of sequentially, can significantly reduce the complexity of the reaction procedure or provide special molecular architectures that would be otherwise very difficult to synthesize. Atom transfer radical polymerization, ATRP, has been widely applied in concurrent polymerization reactions and resulted in improved efficiency in macromolecular engineering. This perspective summarizes reported studies employing concurrent polymerization methods with ATRP as one of the reaction components and highlights future research directions in this area.

Transparency and AIE tunable supramolecular polymer hydrogel acts as TEA-HCl vapor controlled smart optical material

Stimuli-responsive optical materials attract lots of attention due to their broad applications. Herein, a novel smart stimuli-responsive supramolecular polymer was successfully constructed using a simple tripodal quaternary ammonium-based gelator (TH). The TH self-assembles into a supramolecular polymer hydrogel (TH-G) and shows aggregation-induced emission (AIE) properties. Interestingly, the transparency and fluorescence of the TH-G xerogel film (TH-GF) could be reversibly regulated by use of triethylamine (TEA) and hydrochloric acid (HCl) vapor. When alternately fumed with TEA and HCl vapor, the optical transmittance of the TH-GF was changed from 8.9% to 92.7%. Meanwhile, the fluorescence of the TH-G shows an "ON/OFF" switch. The reversible switching of the transparency and the fluorescence of the TH-GF is attributed to the assembly and disassembly of the supramolecular polymer TH-G. Based on these stimuli-response properties, the TH-GF could act as an optical material and shows potential applications as smart windows or fluorescent display material controlled by TEA and HCl vapor.

Facile construction of a double network cross-linked luminescent supramolecular elastomer by hydrosilylation and pillar[5]arene host-guest recognition

Reticulated copolymer host pillar[5]arene cross-linked with poly(dimethylsiloxane) (PDMS) was synthesized for the facile construction of a double network cross-linked elastomer upon noncovalently cross-linking with tetraphenyethylene (TPE)-based tetratopic guests through host-guest interactions. The obtained sample strips had better mechanical properties and luminescence capabilities.

Dynamic Assemblies of Molecular Motor Amphiphiles Control Macroscopic Foam Properties

Stimuli-responsive supramolecular assemblies controlling macroscopic transformations with high structural fluidity, i.e., foam properties, have attractive prospects for applications in soft materials ranging from biomedical systems to industrial processes, e.g., textile coloring. However, identifying the key processes for the amplification of molecular motion to a macroscopic level response is of fundamental importance for exerting the full potential of macroscopic structural transformations by external stimuli. Herein, we demonstrate the control of dynamic supramolecular assemblies in aqueous media and as a consequence their macroscopic foam properties, e.g., foamability and foam stability, by large geometrical transformations of dual light/heat stimuli-responsive molecular motor amphiphiles. Detailed insight into the reversible photoisomerization and thermal helix inversion at the molecular level, supramolecular assembly transformations at the microscopic level, and the stimuli-responsive foam properties at the macroscopic level, as determined by UV-vis absorption and NMR spectroscopies, electron microscopy, and foamability and in situ surface tension measurements, is presented. By selective use of external stimuli, e.g., light or heat, multiple states and properties of macroscopic foams can be controlled with very dilute aqueous solutions of the motor amphiphiles (0.2 weight%), demonstrating the potential of multiple stimuli-responsive supramolecular systems based on an identical molecular amphiphile and providing opportunities for future soft materials.

Supramolecular Prodrug Nanovectors for Active Tumor Targeting and Combination Immunotherapy of Colorectal Cancer

Immunotherapy aiming to harness the exquisite power of the immune system has emerged as a crucial part of clinical cancer management. However, only a subset of cancer patients responds to current immunotherapy because of low immunogenicity of the tumor cells and immunosuppressive tumor microenvironment. Herein, host-guest prodrug nanovectors are reported for active tumor targeting and combating immune tolerance in tumors. The prodrug nanovectors are designed by integrating hyaluronic acid (HA) and reduction-labile heterodimer of Pheophorbide A (PPa) and NLG919 into the supramolecular nanocomplexes, where PPa and NLG919 act as a photosensitizer and potent inhibitor of indoleamine 2,3-dioxygenase 1 (IDO-1), respectively. Meanwhile, HA is employed to achieve active tumor targeting by recognizing CD44 overexpressed on the surface of tumor cell membranes. Near infrared (NIR) laser irradiation triggers the release of reactive oxygen species to provoke antitumor immunogenicity and intratumoral infiltration of cytotoxic T lymphocytes (CTLs). Meanwhile, the immunosuppressive tumor microenvironment (ITM) is reversed by NLG919-mediated IDO-1 inhibition. Combination of photodynamic immunotherapy and IDO-1 blockade efficiently eradicates CT26 colorectal tumors in the immunocompetent mice. The host-guest nanoplatform capable of eliciting effective antitumor immunity by inactivating inhibitory immune response can be applied to other immune modulators for improved cancer immunotherapy.

Supramolecular materials based on AIE luminogens (AIEgens): construction and applications

The emergence of aggregation-induced emission luminogens (AIEgens) has significantly stimulated the development of luminescent supramolecular materials because their strong emissions in the aggregated state have resolved the notorious obstacle of the aggregation-caused quenching (ACQ) effect, thereby enabling AIEgen-based supramolecular materials to have a promising prospect in the fields of luminescent materials, sensors, bioimaging, drug delivery, and theranostics. Moreover, in contrast to conventional fluorescent molecules, the configuration of AIEgens is highly twisted in space. Investigating AIEgens and the corresponding supramolecular materials provides fundamental insights into the self-assembly of nonplanar molecules, drastically expands the building blocks of supramolecular materials, and pushes forward the frontiers of supramolecular chemistry. In this review, we will summarize the basic concepts, seminal studies, recent trends, and perspectives in the construction and applications of AIEgen-based supramolecular materials with the hope to inspire more interest and additional ideas from researchers and further advance the development of supramolecular chemistry.

Viscoelasticity in associating oligomers and polymers: experimental test of the bond lifetime renormalization model

Recent findings that the association bond lifetimes τα* in associating polymers diverge from their supramolecular network relaxation times τc challenge past theories. The bond lifetime renormalization proposed by Rubinstein and coworkers [Stukalin et al., Macromolecules, 2013, 46, 7525] provides a promising explanation. To examine systematically its applicability, we employ shear rheology and dielectric spectroscopy to study telechelic associating polymers with different main chain (polypropylene glycol and polydimethylsiloxane), molecular weight (below entanglement molecular weight) and end groups (amide, and carboxylic acid) which form dimeric associations by hydrogen bonding. The separation between τc (probed by rheology) and τα* (probed by dielectric spectroscopy) strongly increases with chain length as qualitatively predicted by the model. However, to describe the increase quantitatively, a transition from Rouse to reptation dynamics must be assumed. This suggests that dynamics of super-chains must be considered to properly describe the transient network.

Pillar[5]arene-based self-assembled linear supramolecular polymer driven by guest halogen–halogen interactions in solid and solution states

A pillar[5]arene-based linear supramolecular polymer mediated by guest halogen–halogen interactions (C–Br⋯Br–C) was studied in both the solution and solid states.

Light-controlled switchable complexation by a non-photoresponsive hydrogen-bonded amide macrocycle

A light controlled switchable host–guest system based on a non-photoresponsive H-bonded macrocycle and pyridinium salts was developed using a photoacid.

Preparation of a mechanically interlocked polymer from a linear supramolecular polymer

We transformed a linear supramolecular polymer into a mechanically interlocked polymer by photoisomerization.