Recent development of pillar[n]arene-based amphiphiles

Pillar[n]arene-based amphiphiles,mainly including amphiphilic pillar[n]arenes and supra-amphiphilic pillar[n]arenes,have obtained considerable interests in recent years due to their fascinating chemical structures,various self-assembly behaviors,and widely applications.Thanks to the pillar-like frameworks and the rich host-guest recognitions of the cavities,these amphiphiles can be easily controlled to form dimensional and morphologic assemblies for multiple applications.Compared with traditional linear covalent amphiphiles,the introduction of host-guest recognitions facilitated the preparation and controllability of these supramolecular amphiphilic systems.Moreover,the host-guest recognitions endow the assemblies from pillar[n]arene-based amphiphiles with stimuli-responsive functions.In this mini-review,we summarized the chemical structures,self-assembly features,and the applications of pillar[n]arene-based amphiphiles.However,several research topics of pillar[n]arenebased amphiphiles can be further developed in the future,such as larger cavity amphiphilic pillar[n]arenes,co-assembly with 2 D materials and utilization of the host-guest interactions.     

Guest induced morphology transitions of star shaped pillar[5]arene trimer via endo host-guest and "exo-wall" electron-transfer interactions

Star shape bridged pillar[5]arene trimer(C3-PLT) based on benzene-1,3,5-tricarboxamide(BTAs) was successfully synthesized,which exhibited outstanding guest responsive morphology transition properties.The morphology tining studies was efficiently achieved with the addition of competitive guest molecules G1 and G2 by various self-assembly mechanisms.C3-PLT itself displays nanofiber morphology through H-type π-π stacking,and this nanofiber morphology can be completely transformed into spherical vesicles by host-guest interaction Gl,while upon addition of G2 into C3-PLT by means of "exo-wall" electron-transfer interactions,sheet superstructures can be observed.SEM,~1 H NMR,DOSY,fluorescence spectroscopy,and viscosity have verified the formation of supramolecular polymers and morphological transitions between C3-PLT with both guests.     

Axle length- and solvent-controlled construction of (pseudo)[1]rotaxanes from mono-thiourea-functionalised pillar[5]arene derivatives

A series of thiourea-functionalised pillar[5]arene derivatives 3ⁿm were constructed from a series of mono-amide-functionalised pillar[5]arenes 2ⁿ. The formation of their free forms or (pseudo)[1]rotaxane structures were controlled by their axle lengths or solvents, which were investigated by ¹H NMR spectroscopy. Some of (pseudo)[1]rotaxane structures were also supported by their single-crystal structures.     

Synthesis of pillar[7]arene

The first synthesis of pillar[7]arene is reported with two methods.Method A:the FeCl₃-catalyzed condensation reaction of 1,4- dimethoxybenzene（1） with paraformaldehyde in CHCl₃ gave dimethoxypillar[7]arene（3）.Method B:the p-toluenesulfonic acid catalyzed condensation reaction of 2,5-bis（benzyloxymethyl）-1,4-dimethoxybenzene（2） in CH₂Cl₂ gave compound 3.Demethylation of 3 with BBr₃ gave pillar[7]arene（4）.The pillar[7]arene might be a perspective macrocyclic host in host-guest chemistry.     

Design and synthesis of self-included pillar[5]arene-based bis-[1]rotaxanes

Two strategies for the design of new pillar[5]arene-based mechanically self-interlocked molecules (MSMs) are reported here. The first strategy is based on the construction of an intermediate pseudo[1]rotaxane followed by the desired bis-[1]rotaxane. The other one is based on the construction of the desired bis-[1]-rotaxane directly via a condensation reaction through host-guest interactions between a mono-functionalized pillar[5]arene and the axle. This compound has interesting self-assembly properties in methanol and some extended applications of this compound will be reported in the near future.     

Supramolecular control over LCST behavior of hybrid macrocyclic system based on pillar[5]arene and crown ether

A hybrid system containing a pillar[5]arene unit and ten crown ether moieties was developed. The LCST behavior and thermo-responsiveness were successfully introduced into this pillar[5]arene-crown ether system. Both host-guest interactions and salting-out effect displayed great effects in realizing the supramolecular control over LCST properties and thermo-responsiveness. Compared with the individual macrocycles, this hybrid macrocycle system dramatically amplified the supramolecular control effect over LCST behavior.     

Monofunctionalized pillar[5]arene-based stable [1]pseudorotaxane

A new monofunctionalized pillar[5]arene bearing imidazolium moiety that formed stable [1]pseudorotaxane even at high concentration (100 mmol/L) was reported. [1]Rotaxane was obtained effi ciently through thiol-ene reaction from [1]pseudorotaxane which further confi rmed the formation of [1]pseudorotaxane.     

Synthesis and characterization of a new pillar[5]arene-based [1]rotaxane

In this study, we reported the synthesis of three kinds of mono-functional pillar[5]arene derivatives PRI, PRII and R and their structures were studied by 1D and 2D NMR spectra and mass spectra. The 2D NMR spectra including ¹H-¹³C HSQC, ¹H-¹H COSY and NOESY spectra indicated that PRI and PRII are both stable self-included pseudo[1]rotaxanes in CDCl₃. These original structures are promising compounds for the design of pillar[5]-based [1]rotaxane. And the results showed that R could exist stable in CDCl₃ and DMSO because of the coordination of N-H?O hydrogen bonding interaction and C-H?π interaction.     

A Bodipy-bearing pillar[5]arene for mimicking photosynthesis: Multi-fluorophoric light harvesting system

Herein, we submitted to the original synthesis, characterization, energy transfer mechanism of the Bodipy-bearing pillar[5]arene Bodipy and its reactants by employing of infrared, ¹H, ¹¹B, ¹³C, ¹⁹F-NMRs, UV–vis, fluorescence spectroscopy, melting point apparatus, CHN elemental analysis and mass spectroscopy. Preliminary UV–vis, fluorescence and excitation measurements were carried out in CH₂Cl₂ and the results revealed an effective fluorescence resonance energy transfer (FRET) system based on the interaction of pillar[5]arene and Bodipy derivative. ε_max of target molecule reached to a maximum value and it was found as 955 000?M^?1?cm^?1. This fluorescent macromolecule worked well for mimicking a light harvesting system with an energy transfer efficiency up to 92%.     

Enhanced head-to-head photodimers in the photocyclodimerization of anthracenecarboxylic acid with a cationic pillar[6]arene

The complexation behaviors of anthracenecarboxylic acid and water-soluble cationic pillararenes have been investigated by ¹H NMR, UV-vis and ITC methods. The cationic pillar[6]arene was found to stepwise form 1:1 and 1:2 complexes, having a large K₁ and a relatively small K₂ values. Photocyclodimerization of AC within the pillar[6]arene improved the yield of the head-to-head photodimers. Up to 4.97 HH/HT ratio has been reached by optimizing the reaction conditions.     

A one-pot synthesis of a self-included bisester-functionalized copillar[5]arene

A bisester-substituted copillar[5]arene was synthesized by a one-pot reaction presenting a symmetrical selfincluded conformation in solution and an asymmetrical structure with only one selfincluded side in the cavity of pillar[5]arene in the solid state. This compound was characterized by 1D and 2D NMR and X-ray diffraction.     

Experimental and computational investigations on the high binding-selectivity of pyrimidine derivatives by a pillar[5]arene

The binding selectivity of an adenine-monofunctionalized pillar[5]arene (H) with a series of pyrimidine derivatives were investigated through ¹H NMR experiments and density functional theory (DFT) study. High binding-selectivity was demonstrated. Typically, H displayed very strong binding strength with 6-(2,4-dioxo-3, 4-dihydropyrimidin-1 (2H)-yl)hexanenitrile (G1) [K_a >10⁵ M^?1], up to about 3000-fold as compared with 1-hexylpyrimidine-2,4(1H, 3H)-dione (G5) [K_a = 31 M^?1]. The strong binding ability of H with G1 was due to the cooperative multiple hydrogen bond, dipole-dipole, C-H···π and π···π interactions. The high binding-selectivity was also verified by calculation results. The calculated interaction energy (ΔE_i) of G1?H was ?12.92 Kcal·mol^?1 while that of G5?H was ?2.85 Kcal·mol^?1.     

Pillar[5]arene based conjugated macrocycle polymers with unique photocatalytic selectivity

The development of heterogeneous catalysts with substrate shape, size or electronic constitution selectivity is a huge challenge in photocatalysis. Reported herein is a host-guest interaction strategy to endow photocatalysts with special selectivity. By adjusting the precursors, conjugated macrocycle polymers (CMPs) with pillar[5]arene struts (CMP-1 and CMP-2) and a corresponding non-pillar[5]arene-contained conjugated organic polymer (COP-1) were prepared and the photocatalytic activities toward sulfide derivatives were investigated. The sulfides showed similar conversions when COP-1 was used as a photocatalyst, but exhibited significant differences when it turned to the CMPs. Remarkably, the conversion yield of S-1 achieved near 18 folds over the one of S-2 when CMP-2 was used as a catalyst. Mechanism studies confirmed that the “host-guest” effect of pillar[5]arene struts in CMPs was the main cause of the difference. The present work establishes CMPs as novel heterogeneous photocatalysts with substrate selectivity, and such a method will inspire the researchers concerning preparation of heterogeneous catalysts with excellent selectivity.     

Supramolecular assemblies based on some new methyl-substituted cucurbit[5]urils through hydrogen bonding

Three supramolecular assemblies based on three new partial methyl-substituted cucurbit[5]urils, which are tetramethylcucurbit[5]uril (α,γ-TMeQ[5]), hexamethyl cucurbit[5]uril (α,β,δ-HMeQ[5]), Nonamethylcucurbit[5]uril (NMeQ[5]), were synthesized and structurally characterized by single-crystal X-ray diffractions. For the comparison with these new Q[5]s, crystal structure of an assembly constructing with normal Q[5] and K₂PtCl₆ was also reported. They are (α,γ-TMeQ[5])·15(H₂O) (1), (α,β,δ-HMeQ[5])·2Cl⁻·2(H₃O)⁺·7(H₂O) (2), (NMeQ[5])·14(H₂O) (3), (4). In the corresponding crystal structures, the molecular encapsulates included a water molecule and lidded water molecules at both of the portals were observed. Moreover, these molecular encapsulates are connected through hydrogen bonding and formed supramolecular chains or joined in pair.     

Synthesis of a functionalised calix[4]arene and its interactions with hemicucurbit[6,7]urils and cucurbit[8]uril

In the present work, we synthesised a functionalised calix[4]arene with 5,11-di(N-methyl-E-(4-pyridylethylene) moiety (CX[4]), and investigated interactions of it with HemiMeQ[6], HemiMeQ[7], and Q[8]) in both water and DMSO using fluorescence spectrophotometry and ¹H NMR spectroscopy. Titration ¹H NMR spectra revealed that Q[n]s prefers to include the N-methyl-E-(4-pyridylethylene) moiety. In particular, the interaction of CX[4] with Q[8] in water resulted in intense fluorescence emission, and this interaction system can respond to compounds such as amantadine.     

Self-assembly and proton conductance of organic nanotubes from pillar[5]arenes

Organic nanotubes have been assembled from pillar[5]arenes 1 and 2. Compound 1 gelates organic solvents through the formation of tubular fibers which are evidenced by TEM and XRD experiments, while 2 assembles into two different channels under the template effect of water wires. In addition, the water wires in the nanotubes of 2 can be under selective proton conductance. The results described herein represent a new strategy for building tubular structures.     

Pillar[5]arene based conjugated macrocycle polymers with unique photocatalytic selectivity

The development of heterogeneous catalysts with substrate shape, size or electronic constitution selectivity is a huge challenge in photocatalysis. Reported herein is a host-guest interaction strategy to endow photocatalysts with special selectivity. By adjusting the precursors, conjugated macrocycle polymers (CMPs) with pillar[5]arene struts (CMP-1 and CMP-2) and a corresponding non-pillar[5]arene-contained conjugated organic polymer (COP-1) were prepared and the photocatalytic activities toward sulfide derivatives were investigated. The sulfides showed similar conversions when COP-1 was used as a photocatalyst, but exhibited significant differences when it turned to the CMPs. Remarkably, the conversion yield of S-1 achieved near 18 folds over the one of S-2 when CMP-2 was used as a catalyst. Mechanism studies confirmed that the “host-guest” effect of pillar[5]arene struts in CMPs was the main cause of the difference. The present work establishes CMPs as novel heterogeneous photocatalysts with substrate selectivity, and such a method will inspire the researchers concerning preparation of heterogeneous catalysts with excellent selectivity.     

A pillar[5]arene-based molecular grapple of hexafluorophosphate

A symmetric pillararene-based receptor formed 1:1 complexes instead of 1:2 with different halide anions. The cooperative multivalent hydrogen-bond interactions changed its structure from pillar to conical. By the addition of F, it can work like an excavator grapple selectively grasps a PF₆^- anion.     

Novel fluorescent supramolecular polymer metallogel based on Al3+ coordinated cross-linking of quinoline functionalized- pillar[5]arene act as multi-stimuli-responsive materials

A novel supramolecular polymer metallogel ( QP5-AlG ) has been constructed by cross-linking of bis-8-hydroxyquinoline functionalized pillar[5]arene with Al³⁺. The metallogel QP5-AlG shows light blue aggregation induced emission (AIE) in DMSO/H₂O binary solution. Interestingly, the QP5-AlG shown multiple external stimuli-responsive behaviors such as temperature, guest compounds, acid, base and so on. The QP5-AlG can be used as a fluorescent material for detection of Fe³⁺, F^-, trifluoroacetic acid (TFA) and triethylamine (TEA) by different fluorescence states (“on” or “off”). The (limits of lowest detection) LOQs of the QP5-AlG for Fe³⁺, F^-, TFA and TEA are in the range of 4.39 × 10^-9-1.82 × 10^-7 M. More interestingly, a QP5-AlG -based rewritable and erasable fluorescent platform was demonstrated, which offers a potential testbed for performing “write-erase-write” cycles multiple times. This study provides insight into the development of novel multifunctional supramolecular materials.     

Supramolecular amphiphilies based on water-soluble pillar[5]arene/paraquat derivatives and their self-assembly behaviour in water

Supramolecular amphiphilies based on water-soluble pillar[5]arene/paraquat derivatives were successfully prepared. We found that when the length of the alkyl chain on guest molecules shorter than C₁₂, it formed micelles, on the other hand, when the alkyl chain longer than C₁₂, vesicles were obtained. Furthermore, we have demonstrated that the resulting vesicles can respond to multiple external stimuli, including temperature, host–guest inclusion and pH. Methods of warming, decreasing the pH of the system and inclusion of α-cyclodextrins were then employed to disrupt the vesicle architecture. Finally, controlled release experiments were performed to evaluate the vesicles which could encapsulate calcein within their interiors under neutral conditions and release it in response to a decrease in pH.