Warm/cool-tone switchable thermochromic material for smart windows by orthogonally integrating properties of pillar[6]arene and ferrocene

Synergistic covalent-and-supramolecular polymers connected by [2]pseudorotaxane moieties

Synergistic covalent-and-supramolecular polymers, in which covalent polymers and supramolecular polymers connect with each other through [2]pseudorotaxane moieties, are designed and synthesized. The unique topological structure effectively enhances the synergistic effect between these two polymers, thereby generating a novel class of mechanically adaptive materials.

Pillar[5]arene-Derived endo-Functionalized Molecular Tube for Mimicking Protein-Ligand Interactions

Artificial tubular molecular pockets bearing polar functionalities on their inner surface are useful model systems for understanding the mechanisms of protein-ligand interactions in living systems. We herein report a pillar[5]arene-derived molecular tube, [P4-(OH)BPO], whose endo conformational isomer endo-[P4-(OH)BPO] possesses an inwardly pointing hydrogen-bond (H-bond) donor (OH) in its deep cavity and a strong H-bond acceptor (C═O) on its predominantly hydrophobic inner surface, rendering it a perfect protein binding pocket mimetic. A fragment-based drug design model was established using endo-[P4-(OH)BPO] and a library of various shape-complementary fragment ligands (1-38). On the basis of the binding affinity data for "fragment-pocket" complexes G⊂endo-[P4-(OH)BPO] (G = 1-38), two rationally designed "lead molecules" (39 and 40) were identified as being able to enhance binding affinity significantly by forming H-bonds with both the donor and acceptor of endo-[P4-(OH)BPO]. The described work opens new avenues for developing pillar[n]arene-derived protein binding pocket-mimetic systems for studies of protein-ligand interactions and mechanisms of enzymatic reactions.

Highly Branched Pillar[5]arene-Derived Porous Aromatic Frameworks (PAFs) for Removal of Organic Pollutants from Water

The adsorption process is widely used for the treatment of wastewater containing organic pollutants. We fabricated highly branched pillar[5]arene-based porous aromatic frameworks (PAFs), PAF-P5, for the adsorption and removal of organic pollutants (short-chain alkyl derivatives 1-3 and pesticide molecules 4-6) from water with high removal efficiency (RE). However, PAF-P5 was incapable of adsorbing aromatic organic dyes 7-9. Adsorption kinetic studies indicated that the adsorption is mainly driven by strong host-guest interactions between 1-3 and the pillar[5]arene units in PAF-P5, while 4-6 only weakly interacted with the pillar[5]arene units in PAF-P5. Moreover, chemically breaking down the pillar[5]arene rings in PAF-P5 caused changes in the pore size, the microenvironment inside of the pores, and the frame morphology, and the resultant frameworks, PAF-DeP5, exhibited poor adsorption toward 1-6 but adsorbed 7-9 possibly through physical adsorption as implied by fitting the experimental data into the adsorption kinetic models.

Thermally Responsive Poly(ethylene oxide)-Based Polyrotaxanes Bearing Hydrogen-Bonding Pillar[5]arene Rings*

Poly(ethylene oxide)s (PEOs) are useful polymers with good water solubility, biological compatibility, and commercial availability. PEOs with various end groups were threaded into pillar[5]arene rings in a mixture of water and methanol to afford pseudopolyrotaxanes. Corresponding polyrotaxanes were also constructed by capping COOH-terminated pseudopolyrotaxanes with bulky amines, in which multiple hydrogen bonds involving the pillar[5]arene OH groups were critically important to prevent dethreading. The number of threaded ring components could be rationally controlled in these materials, providing a simple and versatile method to tune the mechanical and thermal properties. Specifically, a polyrotaxane with a high-molecular-weight axle became elastic upon heating above the melting point of PEOs and exhibited temperature-dependent shape memory property because of the topological confinement and crosslinked hydrogen bonds.

Hydroxypropylmethyl Cellulose Modified with Carbon Dots Exhibits Light-Responsive and Reversible Optical Switching

A light-responsive optical switching material is reported, which was obtained by incorporating carbon dots (CDs) into thermochromic hydroxypropylmethyl cellulose (HPMC). The ultrasmall size of CDs guarantees the considerable transparency of CDs/HPMC. Under illumination, CDs/HPMC shows rapid and reversible optical switching between transparent and opaque states due to the remarkable photothermal effect of CDs. Moreover, the interaction between CDs and HPMC enhances the light absorption and boosts the nonradiative recombination of photoexcited charge carriers that further promote the photothermal conversion of CDs, and also ensures the structural stability of the composite. The obtained CDs/HPMC with good reversibility and high sensitivity which can dynamically switch their transparency in response to weather conditions exhibits excellent solar modulation ability.

Synthesis of Chiral Helic[1]triptycene[3]arenes and Their Enantioselective Recognition Towards Chiral Guests Containing Aminoindan Groups

Starting from the enantiopure precursors, a pair of chiral macrocyclic arenes named helic[1]triptycene[3]arenes were conveniently synthesized. The circular dichroism (CD) spectra of the enantiomeric macrocyclic arenes exhibited mirror images, and the X-ray single crystal structures confirmed their absolute conformations as well. Moreover, the macrocyclic arenes showed strong complexation with secondary ammonium and primary ammonium salts containing aminoindan groups. In particular, the chiral macrocyclic arenes exhibited enantioselective recognition ability towards the chiral secondary ammonium salts containing aminoindan groups with an enantioselective ratio up to 3.89.

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.

Multiple applications of polymers containing electron-reservoir metal-sandwich complexes

Ferrocene-containing polymers have been investigated for more than six decades, and more recently modern synthetic methods have allowed the fabrication of precise polymers that contain a variety of transition-metal complexes. Trends are now oriented towards applications, such as optics, energy conversion and storage, electrochemistry, magnetics, electric conductors and biomedicine. Metal-sandwich complexes such as those of ferrocene type and other related complexes that present redox-robust groups in polymers, i.e. that are isolable in both their oxidized and reduced forms, are of particular interest, because it is possible to address them using electronic or photonic redox stimuli for application. Our research groups have called such complexes Electron-Reservoirs and introduced them in the main chain or in the side chains of well-defined polymers. For instance, polymers with ferrocene in the main chain or in the side chain are oxidized to stable polycationic polyelectrolytes only if ferrocene is part of a biferrocene unit, because biferrocene oxidation leads to the biferrocenium cation that is stabilized by the mixed valency. Then a group of several redox-robust iron sandwich complexes were fabricated and incorporated in precise polymers including multi-block copolymers whose controlled synthesis and block incorporation was achieved for instance using ring-opening-metathesis polymerization. Applications of this family of Electron-Reservoir-containing polymers includes electrochemically induced derivatization of electrodes by decorating them with these polymers, molecular recognition and redox sensing, electrochromics with multiple colours, generation of gold and silver nanoparticles of various size by reduction of gold(iii) and silver(i) precursors and their use for nanocatalysis towards depollution and biomedicine.

Capture of Sulfur Mustard by Pillar[5]arene: From Host-Guest Complexation to Efficient Adsorption Using Nonporous Adaptive Crystals

Sulfur mustard (SM) has been the most frequently used chemical warfare agent. Here, we present the efficient containment of SM and its simulants by per-ethylated pillar[5]arene (EtP5). EtP5 exhibited strong binding abilities toward SM and its simulants not only in solution but also in the solid state. The association constant (Ka) between SM and EtP5 was determined as (6.2 ± 0.6) × 103 M-1 in o-xylene-d10. Single crystal structure of SM@EtP5 showed that a 1:1 inclusion complex was formed, which was driven by multiple C-H···π/Cl/S and S···π interactions. In addition, activated crystal materials of EtP5 (EtP5α) could effectively adsorb SM simulants at solid-vapor phase; powder X-ray diffraction patterns and host-guest crystal structures indicated that the uptake process triggered a solid-state structural transformation. More interestingly, the captured guest molecules could be stably contained in EtP5α for at least 6 months in air at room temperature.

A light-operated pillar[6]arene-based molecular shuttle

A molecular shuttle comprising a pillar[6]arene macrocyclic ring and an axle with two equal-energy-level stations connected by an azobenzene unit was synthesised. The E isomer of the azobenzene functioned as "open gate", allowing the pillar[6]arene ring to rapidly shuttle back-and-forth between the two stations. Ultraviolet irradiation induced photo-isomerisation of the azobenzene from E to Z form. The Z isomer of the azobenzene functioned as a "closed gate", inhibiting shuttling of the pillar[6]arene ring.

Durable and Controllable Smart Windows Based on Thermochromic Hydrogels

In recent years, the use of smart windows to adjust sunlight to achieve energy conversion has received increasing attention. In this paper, a novel smart window was easily prepared by using thermochromic hydrogels as an interlayer and indium tin oxide films as an electric heating layer. The shielding transmission rates of visible and near-infrared light reached 88.3 and 85.4% at the temperature of 25 °C, respectively. However, the transmittance at a light wavelength of 550 nm was greater than 70% after applying voltage. The smart windows with different components could possess thermochromic temperature ranging from 28 to 35 °C, which was suitable for daily life. The smart window could maintain a stable reversible thermochromic transition. Importantly, the time of light transition and the demand of energy efficiency could be adjusted by controlling the magnitude of the output voltage, which benefited the development of energy-efficient materials.

First-Principles Investigations to Evaluate the Spin-Polarized Metal-to-Insulator Transition of Halide Cuprite Perovskites for Smart Windows

Although smart windows have received wide attention as energy-saving devices, conventional metal-to-insulator materials such as VO₂ hinder their commercial usage because of their high transition temperature and low solar energy modulation. Further development can be achieved by finding a new material system that can effectively overcome these limitations. In this study, first-principles density functional theory calculations are used to investigate the possibility of exploiting a spin-polarized band gap material for smart window applications. Halide cuprite perovskites (A₂CuX₄) were chosen because they have a spin-polarized band gap that can be tuned by element selection at sites A and X. Our study shows that the optical transmittance of the insulating phase is increased by a violation of the selection rule. The spin-polarized band gap is closely related to the metal-to-insulator transition temperature and can be modulated by chemical engineering, strain engineering, or both. Therefore, A₂CuX₄ is a promising candidate for smart windows.

Helic[1]triptycene[3]arene: Synthesis, Complexation, and Formation of [2]Rotaxane Shuttle

A new macrocyclic arene, helic[1]triptycene[3]arene H, was conveniently synthesized in 37% yield by a one-pot reaction starting from 2,6-dimethoxyl-3,7-dihydroxymethyltriptycene. Macrocycle H showed fixed conformation in solution and could form 1:1 complexes with a series of neutral guests, secondary ammonium salts, and tertiary ammonium salts in both solution and solid states. The association constants between H and the neutral guests were between (1.23 ± 0.10) × 10² and (4.70 ± 0.47) × 10³ M^-1, while the association constants between H and the ammonium guests were between (1.35 ± 0.12) × 10³ and (1.59 ± 0.14) × 10⁵ M^-1. Moreover, H showed bigger association constants with secondary ammonium salts than those with tertiary ammonium salts possibly because of the steric hindrance effect and multiple intermolecular interactions. The stimuli-responsive complexation between H and the ammonium salts could be controlled by the addition and removal of acids and bases as well. Based on the host-guest complexation between H and the secondary ammonium salt, [2]rotaxane was further synthesized, and its shuttling motion could be efficiently controlled by an acid and base.

Actively Operable Thermoresponsive Smart Windows for Reducing Energy Consumption

Efficient usage of finite energy resources is a core approach for preventing major blackouts caused by a severe lack of energy. Smart windows, which modulate thermal energy transferred from the incident sunlight, have attracted tremendous interest as an alternative technology for resolving the fast-approaching energy crisis by suppressing unnecessary energy usage such as air conditioning or heating inside buildings. Here, we demonstrate a set of materials and design concepts for doubly responsive smart windows, which efficiently reduce the consumption of our limited energy reserves. The proposed smart windows are based on the concept of combining the lower critical solution temperature of thermoresponsive polymer hydrogels and the electrical actuation of graphene-based flexible heaters; this combination serves to actively control the passive-type moving thermoresponsive smart window. The proposed smart windows exhibit a highly tunable transparency of above 90%, which corresponds to an almost instantaneous change from high transmission of the incident light to the complete blockage of its penetration under thermal or electrical stimulation. In particular, when the windows of a mockup house are replaced with the developed flexible smart windows, the increment rate of the indoor temperature under white light irradiation reduces drastically. This type of active light control system is expected to create a new opportunity for achieving cost savings on heating, cooling, and lighting through management of light energy transmitted into the interior of a house.

Synergistic Covalent and Supramolecular Polymers for Mechanically Robust but Dynamic Materials

Nature has engineered delicate synergistic covalent and supramolecular polymers (CSPs) to achieve advanced life functions, such as the thin filaments that assist in muscle contraction. Constructing artificial synergistic CSP materials with bioinspired mechanically adaptive features, however, represents a challenging goal. Here, we report an artificial CSP system to illustrate the integration of a covalent polymer (CP) and a supramolecular polymer (SP) in a synergistic fashion, along with the emergence of notable mechanical and dynamic properties which are unattainable when the two polymers are formed individually. The synergistic effect relies on the peculiar network structures of the SP and CPs, which endow the resultant CSPs with overall improved mechanical performance in terms of the stiffness, strength, stretchability, toughness, and elastic recovery. Moreover, the dynamic properties of the SP, including self-healing, stimuli-responsiveness, and reprocessing, are also retained in the CSPs, thus leading to their application as programmable and tunable materials.

Environmentally stable, photochromic and thermotropic organohydrogels for low cost on-demand optical devices

HYPOTHESIS

The color-changing ability of creatures widely existed in nature has inspired the development of adaptive allochroic materials, which can respond to various external stimuli. Integrating multi-stimuli responsiveness and long-term stability in allochroic system are urgent for practical applications under complex circumstances.

EXPERIMENTS

The photochromic/thermotropic organohydrogels (PTOs) comprised polyacrylamide and cationic cellulose (JR400) were prepared by facile free-radical polymerization and glycerol displacement. The coexisting covalent bonds and noncovalent interactions collaboratively reinforce the networks, endowing the PTOs with boosted stretchability and toughness.

FINDINGS

The photochromic ammonium molybdate (Mo₇) and thermo-sensitive poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EPE) were made into networks. In these cooperative networks, each constituent performed their own function without disruption, including fast photochromism (10 s) and durable thermo-responsiveness. Importantly, the glycerol-water solvent bestowed the distinct anti-freezing (-30 °C) and anti-dehydration performances on the PTOs. Accordingly, the materials could serve as promising rewritable devices for high-resolution and long-term data storage/encryption. Moreover, on-demand PTO windows integrating UV-prevention and solar energy regulation with T_lum (92.96%) and ΔT_sol (46.02%) could create comfortable and healthy environments for occupants. This work offers a new design strategy for low-cost, environmentally stable smart optical devices.

Synergetic effects in the enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid mediated by β-cyclodextrin-pillar[5]arene-hybridized hosts

Tri-cavity hosts consisting of one pillar[5]arene (P5) sandwiched by two β-cyclodextrins (CDs) were synthesized, and their diastereoseparation was successfully accomplished. Photocyclodimerization of 2-anthracenecarboxylate with these hybrid hosts demonstrated the critical dependence of stereoselectivity on the absolute configuration of the central P5 and the conjugating positions on the β-CD, and gave the non-classical HT photodimers in up to 87% ee.

Host-guest interaction-mediated fabrication of a hybrid microsphere-structured supramolecular hydrogel showing high mechanical strength

The introduction of structured microsphere composites into hydrogels is found to improve their mechanical strength capability. Herein, chitosan microspheres were functionalized with poly(acrylamide-co-1-benzyl-3-vinylimidazolium bromide) (CS-P(AM-G)), which was synthesized through an in situ copolymerization of acrylamide and a guest functional monomer. Supramolecular hydrogels were fabricated by dynamic host-guest interactions between guest units and the host molecule cucurbit[8]uril (CB[8]). Investigations on the mechanical properties of the hydrogels show that the tensile stress and the compress stress of the hydrogels are five times higher than those of CB[8] hydrogels without CS, and the healing efficiency of the hydrogels at room temperature is 88% after 24 h. The results show that CS microspheres serve as both polyfunctional initiating and cross-linking centers, whereas the dynamic host-guest interactions endow the hydrogels with a higher self-healing property. The process provides a novel method for the production of tough and self-healing supramolecular hydrogels with various potential applications.

Low-Cost, Robust Pressure-Responsive Smart Windows with Dynamic Switchable Transmittance

Mechanically responsive smart windows with adjustable light transmittance have attracted more and more attention due to their great potential in our daily life. However, their fabrication normally requires complicated preparation such as oxygen plasma treatment and high-cost materials (i.e., poly(dimethylsiloxane) (PDMS)), which hinders their practical applications. Herein, a principally different mechanically responsive smart window, i.e., a pressure-responsive smart window, is reported, which is achieved by harnessing the synergistic interactions (i.e., hydrogen bonding and surface roughness compensation) between the two constituent parts, i.e., hydrogel and agar films. The pressure-responsive smart window features the ultrafast response time (37.5 ms) and high transmittance changes (∼50%) with excellent repeatability, which can be stained with different colors and operated on a flexible substrate. Since the pressure-responsive smart window enables the utilization of the low-cost material and does not require the external energy input, it is anticipated that it may have great potential in practical applications.

Host-Guest Complexation of Perethylated Pillar[6]arene toward Ferrocene Derivatives Both in Solution and Solid State: Different Binding Modes Induced by Minor Structural Changes of Guests

Herein, novel host-guest properties between perethylated pillar[6]arene and four kinds of ferrocene derivatives were fully investigated. NMR titrations, 2D NOESY NMR spectroscopy, and ESI-MS are used to confirm that they indeed formed stable inclusion complexes. Two precious single-crystal structures were obtained and showed that ferrocene derivatives with different chemical structures exhibit different binding modes with perethylated pillar[6]arenes.

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.

Spreading of benquitrione droplets on superhydrophobic leaves through pillar[5]arene-based host–guest chemistry

Spreading of agricultural sprays on plant surfaces is a significant task as it helps decrease pesticide usage and thereby reduces the risk of environmental pollution.

Thermo- and oxidation-sensitive poly(meth)acrylates based on alkyl sulfoxides: dual-responsive homopolymers from one functional group

Alkyl sulfoxide side groups introduce thermo- and oxidation-sensitivity into poly(meth)acrylates, thus realizing new dual-responsive homopolymers based on one functional group.

Flexible and reconfigurable radio frequency electronics realized by high-throughput screen printing of vanadium dioxide switches

Smart materials that can change their properties based on an applied stimulus are in high demand due to their suitability for reconfigurable electronics, such as tunable filters or antennas. In particular, materials that undergo a metal-insulator transition (MIT), for example, vanadium dioxide (VO₂) (M), are highly attractive due to their tunable electrical and optical properties at a low transition temperature of 68 °C. Although deposition of this material on a limited scale has been demonstrated through vacuum-based fabrication methods, its scalable application for large-area and high-volume processes is still challenging. Screen printing can be a viable option because of its high-throughput fabrication process on flexible substrates. In this work, we synthesize high-purity VO₂ (M) microparticles and develop a screen-printable VO₂ ink, enabling the large-area and high-resolution printing of VO₂ switches on various substrates. The electrical properties of screen-printed VO₂ switches at the microscale are thoroughly investigated under both thermal and electrical stimuli, and the switches exhibit a low ON resistance of 1.8 ohms and an ON/OFF ratio of more than 300. The electrical performance of the printed switches does not degrade even after multiple bending cycles and for bending radii as small as 1 mm. As a proof of concept, a fully printed and mechanically flexible band-pass filter is demonstrated that utilizes these printed switches as reconfigurable elements. Based on the ON and OFF conditions of the VO₂ switches, the filter can reconfigure its operating frequency from 3.95 to 3.77 GHz without any degradation in performance during bending.

Metal–organic polyhedra crosslinked supramolecular polymeric elastomers

Supramolecular polymeric elastomers crosslinked by metal–organic polyhedra were developed, featuring not only tunable mechanical properties but also dynamic actuation behaviors.

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions

Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host-guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell-cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.

A new highly transparent injectable PHA-based thermogelling vitreous substitute

Transparency is an important criterion for the application of biomaterials to the eye and essential for use as a vitreous substitute.

Assembly Pattern of Supramolecular Hydrogel Induced by Lower Critical Solution Temperature Behavior of Low-Molecular-Weight Gelator

Although the gelation process and lower critical solution temperature (LCST) behavior are well acknowledged in polymer systems, low-molecular-weight gelators (LMWGs) rarely display LCST behavior during supramolecular gelation. Herein, we report an LMWG system with LCST-type thermoresponsiveness and an LCST-triggered supramolecular gelation process. Temperature plays a crucial role in this system, not only affecting the LCST phase separation but also triggering the gelation process. The backbones (three-dimensional structures) of the resulting hydrogel are the hierarchical assemblies of the LMWG undergoing the LCST phase separation. Hence, the gelation of the LMWG is only realized when the gelation temperature is above the critical transition temperature (T_cloud) of the LCST behavior, which is different from many supramolecular or polymeric hydrogel systems.

Different Modes of Anion Response Cause Circulatory Phase Transfer of a Coordination Cage with Controlled Directionality

Controlled directional transport of molecules is essential to complex natural systems, from cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Now, the transfer of a supramolecular cage is reported with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.

Complexation of 2,6-helic[6]arene and its derivatives with 1,1'-dimethyl-4,4'-bipyridinium salts and protonated 4,4'-bipyridinium salts: an acid-base controllable complexation

2,6-Helic[6]arene and its derivatives were synthesized, and their complexation with 1,1'-dimethyl-4,4'-bipyridinium and protonated 4,4'-bipyridinium salts were investigated in detail. It was found that the helic[6]arene and its derivatives could all form 1:1 complexes with both 1,1'-dimethyl-4,4'-bipyridinium salts and protonated 4,4'-bipyridinium salts in solution and in the solid state. Especially, the helic[6]arene and its derivatives containing 2-hydroxyethoxy or 2-methoxyethoxy groups exhibited stronger complexation with the guests than the other helic[6]arene derivatives for the additional multiple hydrogen bonding interactions between the hosts and the guests, which were evidenced by ¹H NMR titrations, X-ray crystal structures and DFT calculations. Moreover, it was also found that the association constants (K _a) of the complexes could be significantly enhanced with larger counteranions of the guests and in less polar solvents. Furthermore, the switchable complexation between the helic[6]arene and protonated 4,4'-bipyridinium salt could be efficiently controlled by acids and bases.

Acid/base- and base/acid-switchable complexation between anionic-/cationic-pillar[6]arenes and a viologen ditosylate salt

Two new host-guest complexes between water-soluble anionic pillar[6]arene (WP6) or cationic pillar[6]arene (CP6) and a viologen ditosylate salt G·2TsO were constructed, among which one formed from WP6 and G2+ ions can be controlled by the sequential addition of an acid and a base (HCl and NaOH, respectively), whereas the other fabricated from CP6 and TsO- ions can be switched through the sequential addition of basic and acidic reagents (NaOH and HCl, respectively).

Pillar[5]arene-based spongy supramolecular polymer gel and its properties in multi-responsiveness, dye sorption, ultrasensitive detection and separation of Fe3

Herein, a novel way to design and construct multi-functional spongy supramolecular polymer gels through an easy to make tripodal guest (TA) and a naphthalimide functionalized-pillar[5]arene host (AP5) has been developed. According to this approach, a novel pillar[5]arene-based supramolecular polymer gel (SHG) was constructed via multi-non-covalent interactions such as host-guest inclusion, C-Hπ, ππ and hydrogen bonds and so on. Interestingly, the SHG exhibits a spongy structure and strong aggregation induced emission (AIE). Furthermore, the SHG also exhibited multi-responsiveness toward outer stimuli such as heating-cooling, pH, competitive agents and mechanical. More importantly, the SHG xerogel shows separation properties for Fe3+, methyl orange, methylene blue and sudan I dyes. The separation rates of SHG xerogel for Fe3+ ions and organic dyes can reach up to 99.8%. Simultaneously, the SHG could ultrasensitively detect Fe3+ (LOD is 0.9 nM). In addition, a thin film based on SHG was also prepared, which was confirmed to be a convenient test kit for detecting Fe3+.