Tunable Water‐Soluble Supramolecular Polymers by Visible‐Light‐Regulated Host–Guest Interactions

The development of artificial self‐assembling systems with dynamic photo‐regulation features in aqueous solutions has drawn great attention owing to the potential applications in fabricating elaborate biological materials. Here we demonstrate the fabrication of water‐soluble cucurbit[8]uril (CB[8])‐mediated supramolecular polymers by connecting the fluorinated azobenzene (FAB) containing monomers through host‐enhanced heteroternary π–π stacking interactions. Benefiting from the unique visible‐light‐induced E→Z photoisomerization of the FAB photochromophores, the encapsulation behaviors between the CB[8] macrocycle and the monomers could be regulated upon visible light irradiation, resulting in the depolymerization of such CB[8]‐mediated supramolecular polymers.     

Cucurbit[8]uril-induced diarylethene thermally activated delay fluorescence supramolecular switch for sequential energy transfer

Constructing molecular switches based on supramolecular assembly strategy is a research hotspot. In this work, we constructed an all visible-light-regulated supramolecular photo-switch based on pyridinium-modified diarylethene derivative (DTE-Me) and cucurbit[8]uril (CB[8]). CB[8] not only accelerated the photochromic process under 365 nm ultraviolet light but also shifted the absorption of open formed DTE-Me to the visible region, which led to efficient photocyclization under 450 nm visible light irradiation, while DTE-Me and DTE-Me/CB[7] remained unchanged under the same irradiating condition. Moreover, the complexation with CB[8] could induce the strong thermally activated delayed fluorescence (TADF) of guest molecular at 550 nm, which further shifted to 670 nm through two-step sequential energy transfer with sulforhodamine B (SRB) and Cy5. This energy transfer process could also be regulated with visible light, and the application for information encryption was also demonstrated. This assembly provides a convenient approach to construct all visible light-regulated TADF photo-switch.     

Influence of self-assembly of amphiphilic imidazolium ionic liquids on their host–guest complexes with cucurbit[n]urils

Two symmetric amphiphilic imidazolium ionic liquids having ω-undecenyl chains form supramolecular complexes with CB[7] and CB[8] in water as revealed by ¹H NMR spectroscopy and MALDI-MS. Binding constants in the range 10⁴ to 10⁵ M^?1 were estimated from the conductivity measurements for the 1:1 complexes of these imidazolium ionic liquids with CB[7] and CB[8]. Radical initiated polymerization of these host–guest complexes at concentrations above the critical self-assembly concentration of imidazolium ionic liquids to form liposomes, destroys completely (CB[7]) or partially (CB[8]) the host–guest ionic liquid@CB[n] complex; this behaviour was proved by titration with acridine orange tricyclic dye, of CB[n]s in the colloidal solutions of the liposomes before and after performing dialysis to remove free CB[n]s. Thus, the increase in the fluorescence emission of acridine orange by CB[7] is not observed if the polymerized ionic liquid@CB[7] complex is submitted to dialysis to remove uncomplexed CB[7]. Analogous study by titration of absorbance change of acridine orange solutions caused by CB[8], reveals only a partial destruction of the host–guest complex by self-assembly of amphiphilic ionic liquid above the critical self-assembly concentration. The results obtained have been rationalized considering that the driving force for the formation of supramolecular ionic liquid@CB[n] complexes is a hydrophobic interaction between the apolar alkenyl chain and the cucurbituril interior cavity and that these hydrophobic interactions are disturbed when self-assembly leading to liposomes occurs.     

Supramolecularly Bonded Layered Heterostructures Exhibiting HER Activity

van der Waals heterostructures formed by 2D materials have attracted much attention in the last few years. Recently, 2D nanosheets linked by covalent bonds have been found to exhibit novel properties. In the present study we have investigated supramolecular layered heterostructures formed by nanosheets of MoS₂ with BC₇N, g‐C₃N₄ and graphene. These materials have been synthesized via a non‐covalent host–guest synthetic design using cucurbit[8]uril (CB[8]) hosts. In addition to offering reversible disassembly, these heterostructures show good visible‐light‐driven hydrogen evolution reaction (HER) activity as well as reasonable gas adsorption and other properties.     

Cucurbituril‐Modulated Supramolecular Assemblies: From Cyclic Oligomers to Linear Polymers

Employing bis(p‐sulfonatocalix[4]arenes) (bisSC4A) and N′,N′′hexamethylenebis(1‐methyl‐4,4′‐bipyridinium) (HBV⁴⁺) as monomer building blocks, the assembly morphologies can be modulated by cucurbit[n]uril (CB[n]) (n=7, 8), achieving the interesting topological conversion from cyclic oligomers to linear polymers. The binary supramolecular assembly fabricated by HBV⁴⁺ and bisSC4A units, forms an oligomeric structure, which was characterized by NMR spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and gel permeation chromatography (GPC) experiments. The ternary supramolecular polymer participated by CB[8] is constructed on the basis of host–guest interactions by bisSC4A and the [2]pseudorotaxane HBV⁴⁺@CB[8], which is characterized by means of AFM, DLS, NMR spectroscopy, thermogravimetric analysis (TGA), UV/Vis spectroscopy, and elemental analysis. CB[n] plays vital roles in rigidifying the conformation of HBV⁴⁺, and reinforcing the host–guest inclusion of bisSC4A with HBV⁴⁺, which prompts the formation of a linear polymer. Moreover, the CB[8]‐participated ternary assembly could disassemble into the molecular loop HBV²⁺@CB[8] and free bisSC4A after reduction of HBV⁴⁺ to HBV²⁺, whereas the CB[7]‐based assembly remained unchanged after the reduction. CB[8] not only controlled the topological conversion of the supramolecular assemblies, but also improved the redox‐responsive assembly/disassembly property practically.     

Tunable Nanosupramolecular Aggregates Mediated by Host–Guest Complexation

Nanosupramolecular assemblies with controlled topological features have inventive applications in fundamental studies and material manufacturing. Herein, a variety of morphologically interesting aggregates have been constructed using the supramolecular modulation with bipyridinium‐modified diphenylalanine derivative (BP‐FF). Benefiting from the high binding affinity of bipyridinium group with four different macrocyclic receptors, namely cucurbit[7]uril, cucurbit[8]uril, pillar[5]arene, and tetrasulfonated crown ether, we have succeeded in tuning the topological aggregates of BP‐FF from fine nanofibers to nanorods, octahedron‐like nanostructure, helical nanowires, and rectangular nanosheets without any tedious chemical modification. This supramolecular approach may provide us a powerful method to construct well‐defined nanostructures with different morphologies that can be conveniently controlled by facile host–guest interactions.     

Visible‐Light‐Excited Room‐Temperature Phosphorescence in Water by Cucurbit[8]uril‐Mediated Supramolecular Assembly

Solid‐state materials with efficient room‐temperature phosphorescence (RTP) emissions have found widespread applications in materials science, while liquid or solution‐phase pure organic RTP emission systems has been rarely reported, because of the nonradiative decay and quenchers from the liquid medium. Reported here is the first example of visible‐light‐excited pure organic RTP in aqueous solution by using a supramolecular host‐guest assembly strategy. The unique cucurbit[8]uril‐mediated quaternary stacking structure allows tunable photoluminescence and visible‐light excitation, enabling the fabrication of multicolor hydrogels and cell imaging. The present assembly‐induced emission approach, as a proof of concept, contributes to the construction of novel metal‐free RTP systems with tunable photoluminescence in aqueous solution, providing broad opportunities for further applications in biological imaging, detection, optical sensors, and so forth.     

Targeted Polypeptide–Microtubule Aggregation with Cucurbit[8]uril for Enhanced Cell Apoptosis

Tunable protein assemblies not only hold a dominant position in vital biological events but are also a significant theme in supramolecular chemistry. Herein, we demonstrated that the intertubular aggregation of microtubules (MTs) could be efficiently regulated by a synergistic polypeptide–tubulin interaction and host–guest complexation. The benzylimidazolium‐modified antimitotic peptide (BP) could recognize the MTs and concurrently form stable inclusion complexes with avirulent cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) in different binding stoichiometries. The self‐assembling morphology of MTs was converted from fibrous to nanoparticulate aggregates via extensive BP?CB[8] cross‐linkage, leading to significant cell apoptosis and tumor ablation in vivo. The targeted (BP?CB[8])@MT ternary assembly provides a facile supramolecular method to enhance the protein–protein interactions, which may be developed as a therapy for degenerative diseases, such as cancer.     

Inclusion of Carboxyl Function Inside of Cucurbiturils and its Use in Molecular Switches

We have prepared organic guest molecules in which two pyridinium rings are connected through an aromatic/aliphatic bridge bearing a carboxyl group. The supramolecular interactions between these guests and macrocyclic hosts cucurbit[7]uril ( CB7 ) and cucurbit[8]uril ( CB8 ) has been studied. We have demonstrated that the binding modes of the complexes depend on the type of central bridge present in the guest molecules and the size of the macrocycle. We have also showed that the binding mode between cucurbiturils and guests with aromatic bridges is pH independent. On the other hand, a guest containing an aliphatic bridge and CB7 formed a pseudorotaxane, which behaved as a pH‐driven molecular switch.     

Responsiveness and Morphology Study of Dual Stimuli‐Controlled Supramolecular Polymer

The synthesis and characterization of a linear supramolecular polymer formed by dual host–guest recognitions is presented. The polymer linked by the orthogonal interactions of azobenzene with β‐cyclodextrin and methyl viologen with sulfonatocalix[4]arene is constructed, and the morphology change along with the formation and vanishment of host–guest interaction is investigated. The reversible disassembly–reassembly of the polymer induced by light and the redox process are monitored by UV–vis and cyclic voltammetry, respectively. The interesting morphology differences between the monomer guest (G), supramolecular polymer (P), and light dissembled product pseudorotaxane (D1) are observed and analyzed. G conducts self‐assembly into a short rod with average width of 83 nm due to the molecular amphipathy and π–π interaction between naphthalene nucleuses, while P exhibits 20 nm wide line morphology. Irradiating P with 365 nm light, the corresponding aggregation D1 shows as 35 nm wide short rod.     

紫精与八元瓜环的超分子组装及光切割质粒DNA

利用紫精可以活化水中溶解氧的特性, 设计合成了苯-紫精化合物(BEV). 利用紫外吸收、电化学及核磁等方法研究了BEV与八元瓜环CB[8] 之间的相互作用. 实验结果表明, 2种化合物可以进行主客体超分子自组装形成1∶ 1的二元包合物BEV-CB[8]. 同时, 分别考察了化合物BEV和BEV-CB[8]与小牛胸腺DNA的相互作用, 并采用琼脂糖凝胶电泳研究了氙灯光照下化合物对pBR322 DNA的切割能力. 结果表明, CB[8]的引入改变了化合物BEV与DNA的作用方式, 使嵌入作用和静电作用增强. 光照结果说明只有超分子BEV-CB[8]在光照下可以完全切割质粒DNA, 即CB[8]的存在明显提高了BEV对质粒DNA的切割效率.     

Enhanced Solution and Solid-State Emission and Tunable White-Light Emission Harvested by Supramolecular Approaches

Organic luminescent materials with high quantum yields and/or white-light-emitting properties in particular play a crucial role in labeling and optoelectronic devices. In this work we have synthesized a new 2,3,6,7-tetramethoxy-9,10-di-p-tolylanthracene-bridged pillar[5]arene dimer with persistent mazarine blue fluorescent emission and much higher quantum yields in both solution and the solid state in comparison with its corresponding emissive linker without pillarene units, which exhibits typical aggregation-caused quenching. According to the fluorescence data and single-crystal analyses, their contrasting fluorescent performances can be rationally ascribed to their different stacking structures and intermolecular interactions. Three fluorescent guests containing different chromophores and/or terminal binding sites have also been synthesized to interact with the pillar[5]arene dimer to construct supramolecular ensembles with highly controllable luminescence, taking advantage of the stimuli-responsive properties of the supramolecular host–guest interactions. Intriguingly, multicolor fluorescence, including white-light emission (0.31, 0.35), which is in high demand, has been achieved by tuning the molar ratio of the host and guest and/or by changing the solvent system. This strategy holds great potential for the design and development of fluorescent materials with high quantum yields, controllable emission wavelength, and good stimuli-responsiveness.     

Construction of unsymmetrical bis-urea macrocyclic host for neutral molecule and chloride-ion binding

Construction of synthetic macrocyclic host that can bind with neutral molecules and anions has potential applications in supramolecular chemistry. Herein, we have designed and synthesized blue light emitting an unsymmetrical neutral bis-urea macrocyclic host. This macrocycle can bind with neutral DMF molecule (1:1) as well as Cl⁻ ion (1:1) through noncovalent interactions. X-Ray crystal structure, ¹H NMR titrations with Job's Plot, HRMS with isotropic distribution pattern, FT-IR, and density functional theory analysis revealed the binding of bis-urea macrocyclic host with the guest molecule.     

A host-induced intramolecular charge-transfer complex and light-driven radical cation formation of a molecular triad with cucurbit[8]uril

The host-guest chemistry of systems containing a molecular triad Ru(bpy) 3-MV (2+)-naphthol complex (denoted as Ru (2+)-MV (2+)-Np, 1) and cucurbit[8]uril (CB[8]) is investigated by NMR, ESI-MS, UV-vis, and electrochemistry. The Ru (2+)-MV (2+)-Np guest and CB[8] host can form a stable 1:1 inclusion complex, in which the naphthalene residue is back-folded and inserted together with the viologen residue into the cavity of CB[8]. The selective binding of Ru (2+)-MV (2+)-Np guest with beta-CD and CB[8] host is also investigated. We find that CB[8] binds the Ru (2+)-MV (2+)-Np guest stronger than beta-CD. Upon light irradiation, a MV (+*) radical cation stabilized in the cavity of CB[8] accompanied by the naphthalene residue has been observed. This novel system may open a new way for design and synthesis of photoactive molecular devices.     

Shape‐Controllable and Fluorescent Supramolecular Organic Frameworks Through Aqueous Host–Guest Complexation

Two kinds of shape‐controllable and fluorescent supramolecular organic frameworks (cuboid or spheroid) are constructed hierarchically from CB[8] and tetraphenylethylene derivatives through host–guest interaction in water. These two fluorescent SOFs exhibit intriguing and varied photophysical properties, including large red‐shifts (up to 82 nm) and stimuli‐responsive behavior to competitive guest by binding with CB[8], the turn‐on fluorescence of which is applied in cellular imaging.     

From Packed “Sandwich” to “Russian Doll”: Assembly by Charge‐Transfer Interactions in Cucurbit[10]uril

As the host possessing the largest cavity in the cucurbit[n]uril (CB[n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron‐rich guests and detail the influence of encapsulation on the charge‐transfer interactions between guests. For the mono‐bipyridinium guest (methylviologen, MV ²⁺), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge‐transfer interactions between methylviologen and dihydroxynaphthalene ( HN ) by mainly forming the 1:2:1 packed “sandwich” complex (CB[10] ? 2 MV ²⁺ ?HN ). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to “U” shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane‐blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X‐ray crystal structure. Finally, a supramolecular “Russian doll” was built up by threading a guest through the cavities of both blue box and CB[10].     

Supramolecular nano drug delivery systems mediated via host-guest chemistry of cucurbit[n]uril (n = 6 and 7)

As a novel family of macrocyclic molecules,cucurbit[n]urils(CB[n]s) have emerged as promising building blocks of supramolecular nano drug delivery systems(SNDDS) in recent years.Direct encapsulation of amphiphilic guests by CB[6] and CB[7] can modulate their amphiphilicity,resulting in formation of supramolecular amphiphiles that self-assemble into supramolecular nanoparticles for drug delivery.Additionally,CB[n]'s host-guest chemistry on the surface of mesoporous nanoparticles makes CB[n] an ideal blocking agent to control drug release from delivery vehicles.These SNDDS possess intrinsic stimuli responsiveness towards external guest or host,which can further incorporate re s ponsiveness to a variety of other stimuli including pH,thermal,redox,photo and enzyme,to realize multiple stimuli-responsive drug release.Moreover,the recent breakthrough in direct functionalization of CB[n]s has provided a feasible method for preparing superior CB[6] and CB[7] derivatives that can be employed to build multifunctional SNDDS with unoccupied macrocycles located on surface,which could be decorated with various functional "tags" through host-guest chemistry.In this review,we summarized the recent progress of CB[6] and CB[7] based SNDDS through formation of supramolecular amphiphiles,supramolecular nanovalves as well as supramolecularly tailorable surface,which we hope to further promote the development of CB[n]s family as building blocks for advanced SNDDS.     

Multistimuli‐Responsive Supramolecular Assembly of Cucurbituril/Cyclodextrin Pairs with an Azobenzene‐Containing Bispyridinium Guest

A linear supramolecular architecture was successfully constructed by the inclusion complexation of α‐cyclodextrin with azobenzene and the host‐stabilized charge‐transfer interaction of naphthalene and a bispyridinium guest with cucurbit[8]uril in water, which was comprehensively characterized by ¹H NMR spectroscopy, UV/Vis absorption, fluorescence, circular dichroism spectroscopy, dynamic laser scattering, and microscopic observations. Significantly, because it benefits from the photoinduced isomerization of the azophenyl group and the chemical reduction of bispyridinium moiety with noncovalent connections, the assembly/disassembly process of this supramolecular nanostructure can be efficiently modulated by external stimuli, including temperature, UV and visible‐light irradiation, and chemical redox.     

Supramolecular Protein Immobilization on Lipid Bilayers

Protein immobilization on surfaces, and on lipid bilayers specifically, has great potential in biomolecular and biotechnological research. Of current special interest is the immobilization of proteins using supramolecular noncovalent interactions. This allows for a reversible immobilization and obviates the use of harsh ligation conditions that could denature fragile proteins. In the work presented here, reversible supramolecular immobilization of proteins on lipid bilayer surfaces was achieved by using the host–guest interaction of the macrocyclic molecule cucurbit[8]uril. A fluorescent protein was successfully immobilized on the lipid bilayer by making use of the property of cucurbit[8]uril to host together a methylviologen and the indole of a tryptophan positioned on the N‐terminal of the protein. The supramolecular complex was anchored to the bilayer through a cholesterol moiety that was attached to the methylviologen tethered with a small polyethylene glycol spacer. Protein immobilization studies using a quartz crystal microbalance (QCM) showed the assembly of the supramolecular complexes on the bilayer. Specific immobilization through the protein N‐terminus is more efficient than through protein side‐chain events. Reversible surface release of the proteins could be achieved by washing with cucurbit[8]uril or buffer alone. The described system shows the potential of supramolecular assembly of proteins and provides a method for site‐specific protein immobilization under mild conditions in a reversible manner.     

Cucurbit[<Emphasis Type="Italic">n</Emphasis>]uril-based host–guest-metal ion chemistry: an emerging branch in cucurbit[<Emphasis Type="Italic">n</Emphasis>]uril chemistry

The unique pumpkin-shape macrocyclic structure with inherent cavities renders cucurbituril (CB) a type of versatile supramolecular container. On account of their good biocompatibility and low toxicity, the applications of CB to encapsulate drug molecules provide promising candidates and the pharmacological activities have been investigated currently. How to control over the uptake and release of the guest at will is significant for practical applications of drug delivery. The noncovalent nature of supramolecular interactions offers variety of options to control the release of guest molecules from CB under external stimuli, including pH, temperature, metal cations, competing guests, light, redox and so on. Moreover, CB containers are capable of assembling into higher ordered supramolecular structures such as polymers, nanoparticles, hydrogels, and colloids, which greatly enrich the scope of CB-type inclusion materials. Those results provide useful principles and guidelines for controlled release from supramolecular containers.