Two‐Component Supramolecular Gels Derived from Amphiphilic Shape‐Persistent Cyclo[6]aramides for Specific Recognition of Native Arginine

A unique supramolecular two‐component gelation system was constructed from amphiphilic shape‐persistent cyclo[6]aramides and diethylammonium chloride (or triethylammonium chloride). This system has the ability to discriminate native arginine from 19 other amino acids in a specific fashion. Cyclo[6]aramides show preferential binding for the guanidinium residue over ammonium groups. This specificity was confirmed by both experimental results and theoretical simulations. These results demonstrated a new modular displacement strategy, exploring the use of species‐binding hydrogen‐bonded macrocyclic foldamers for the construction of two‐component gelation systems for selective recognition of native amino acids by competitive host–guest interactions. This strategy may be amenable to developing a variety of functional two‐component gelators for specific recognition of various targeted organic molecular species.     

Guest⊂Guest⊂Host Multicomponent Molecular Crystals: Entrapment of Guest⊂Guest in Honeycomb Networks Formed by Self‐Assembly of 1,3,5‐Tri(4‐hydroxyaryl)benzenes

Sterically‐engineered rigid trigonal molecular modules based on 1,3,5‐tri(4‐hydroxyphenyl)benzenes H1 and H2 undergo O‐H???O hydrogen‐bonded self‐assembly into eight‐fold catenated hexagonal (6,3) and two‐fold interpenetrated undulated square (4,4) networks, respectively. In the presence of [18]crown‐6 as a guest, the triphenol H1 is found to self‐assemble into a honeycomb network with hexagonal voids created between three triphenol building blocks. The guest [18]crown‐6 molecules are found to be nicely nested in hexagonal enclosures. The empty spaces within the crowns can be further filled with neutral (MeOH/water, MeOH/MeNO₂) or ionic guest species such as KI/KAcAc to furnish novel multicomponent assemblies, that is, guest ? guest ? host, that typify Russian dolls. In contrast, triphenol H2 is found to yield analogous multicomponent molecular crystals in which the guest crown–K⁺ acts as a spacers in the hydrogen‐bonded self‐assembly that leads to distorted chicken wire networks.     

Supramolecular nanostructures from self‐assembly of T‐shaped rod building block oligomers

T‐shaped coil–rod–coil oligomers, consisting of a dibenzo[a,c]phenazine unit and phenyl groups linked together with acetylenyl bonds at the 2,7‐position of dibenzo[a,c]phenazine as a rigid segment have been synthesized. The coil segments of these new molecules composed of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO) incorporating lateral methyl groups between the rod and coil segment and two flexible alkyl groups connecting with the rigid segment at the 4,6‐position of dibenzo[a,c]phenazine, respectively. The experimental results reveal that the length of the flexible PEO coil chain influence construction of various supra‐nanostructures from lamellar structure to rectangular columnar structure. It is also shown that introduction of different length of alkyl side chain groups in the backbone of the T‐shaped molecules affect the self‐organization behavior to form hexagonal perforate layer or oblique columnar structures. In addition, lateral methyl groups attached to the surface of rod and coil segments, dramatically influence the self‐assembling behavior in the crystalline phase. T‐shaped molecules containing a lateral methyl group at the surface of rod and PEO coil segments, self‐assemble into 3D body‐centered tetragonal structures in the crystalline phase, while molecules without a lateral methyl group based on PEO coil chain self‐organize into 2D oblique columnar crystalline structures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5021–5028     

Synthesis and mesomorphic properties of calix[4]resorcinarene–triphenylene oligomers

By controlling the mol ratios of reactants, novel calix[4]resorcinarene–triphenylene monomer, dimer and tetramer were designed and synthesised in yields of 50–60% via Click chemistry. Their structures were characterised by NMR and MS. Their liquid crystalline behaviours were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction analysis. The more triphenylene units on calix[4]resorcinarene resulted in the wider temperature scopes of mesophase and higher phase transition temperatures. The monomer 6 and dimer 7 showed the mixed columnar mesophase with hexagonal columnar structure and disordered lamellar columnar structure, and compound 8 possessed only disordered lamellar columnar mesophase. These research results suggest that calix[4]resorcinarene was a good platform to construct columnar liquid crystal and the mesomorphic properties were greatly influenced by the substituted numbers of mesogen units on calix skeleton.     

Heat‐Triggered Crystallization of Liquid Crystalline Macrocycles Allowing for Conductance Switching through Hysteretic Thermal Phase Transitions

A polymesomorphic thermal phase‐transition of a macrocyclic amphiphile consisting of aromatic groups and oligoethylene glycol (OEG) chains is reported. The macrocyclic amphiphile exists in a highly‐ordered liquid crystal (LC) phase at room temperature. Upon heating, this macrocycle shows phase‐transition from columnar‐lamellar to nematic LC phases followed by crystallization before melting. Spectroscopic studies suggest that the thermally induced crystallization is triggered by a conformational change at the OEG chains. Interestingly, while the macrocycle returns to the columnar‐lamellar phase after cooling from the isotropic liquid, it retains the crystallinity after cooling from the thermally‐induced crystal. Thanks to this bistability, conductance switching was successfully demonstrated. A different macrocyclic amphiphile also shows an analogous phase‐transition behavior, suggesting that this molecular design is universal for developing switchable and memorizable materials, by means of hysteretic phase‐transition processes.     

Complexation Between (O‐Methyl)6‐2,6‐Helic[6]arene and Tertiary Ammonium Salts: Acid/Base‐ or Chloride‐Ion‐Responsive Host–Guest Systems and Synthesis of [2]Rotaxane

Complexation between (O ‐methyl)₆‐2,6‐helic[6]arene and a series of tertiary ammonium salts was described. It was found that the macrocycle could form stable complexes with the tested aromatic and aliphatic tertiary ammonium salts, which were evidenced by ¹H NMR spectra, ESI mass spectra, and DFT calculations. In particular, the binding and release process of the guests in the complexes could be efficiently controlled by acid/base or chloride ions, which represents the first acid/base‐ and chloride‐ion‐responsive host–guest systems based on macrocyclic arenes and protonated tertiary ammonium salts. Moreover, the first 2,6‐helic[6]arene‐based [2]rotaxane was also synthesized from the condensation between the host–guest complex and isocyanate.     

Desymmetrized Leaning Pillar[6]arene

In this work, a novel version of macrocyclic arenes, namely leaning pillar[6]arenes, was discovered and it can be considered as a tilted version of a pillar[6]arene with two hydroxy/alkoxy functionalities removed. Through a facile two‐step synthetic approaches, in conjunction with a diversity of post‐modification possibilities, a series of leaning pillar[6]arenes, with good cavity adaptability and enhanced guest‐binding capability, was synthesized, and their self‐assembly in single‐crystal states is presented. DFT calculations demonstrated that the lower rotational barrier of unsubstituted phenylene rings, the uneven electron density centered at the leaning phenyl rings, and the polarization effect along the edge generated by the hydrogen‐bond‐induced orientation of hydroxy groups greatly affected the host‐guest properties, and meanwhile provided an intuitive explanation for the pillar‐like and rigid structure of traditional pillar[6]arenes. Significantly, the crystal structure of cyclo‐oligomeric quinone was obtained by direct oxidation of leaning pillar[6]arenes.     

Piling Up Pillar[5]arenes To Self‐Assemble Nanotubes

New liquid‐crystalline pillar[5]arene derivatives have been prepared by grafting first‐generation Percec‐type poly(benzylether) dendrons onto the macrocyclic scaffold. The molecules adopt a disc‐shaped structure perfectly suited for self‐organization into a columnar liquid‐crystalline phase. In this way, the pillar[5]arene cores are piled up, thus forming a nanotubular wire encased within a shell of peripheral dendrons. The capability of pillar[5]arenes to form inclusion complexes has been also exploited. Specifically, detailed binding studies have been carried out in solution with 1,6‐dicyanohexane as the guest. Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Col_h mesophase has been deduced from X‐ray diffraction data and found to be similar to that observed within the crystal lattice of a model inclusion complex prepared from 1,4‐dimethoxypillar[5]arene and 1,6‐dicyanohexane.     

Tunable Emissive Lanthanidomesogen Derived from a Room‐Temperature Liquid‐Crystalline Schiff‐Base Ligand

A novel photoluminescent room‐temperature liquid‐crystalline salicylaldimine Schiff base with a short alkoxy substituent and a series of lanthanide(III) complexes of the type [Ln(LH)₃(NO₃)₃] (Ln=La, Pr, Sm, Gd, Tb, Dy; LH=(E)‐5‐(hexyloxy)‐2‐ [{2‐(2‐hydroxyethylamino)ethylimino]methyl}phenol) have been synthesized and characterized by FTIR, ¹H and ¹³C NMR, UV/Vis, and FAB‐MS analyses. The ligand coordinates to the metal ions in its zwitterionic form. The thermal behavior of the compounds was investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The ligand exhibits an enantiotropic hexagonal columnar (Col_h) mesophase at room temperature and the complexes show an enantiotropic lamellar columnar (Col_L) phase at around 120 °C with high thermal stability. Based on XRD results, different space‐filling models have been proposed for the ligand and complexes to account for the columnar mesomorphism. The ligand exhibits intense blue emission both in solution and in the condensed state. The most intense emissions were observed for the samarium and terbium complexes, with the samarium complex glowing with a bright‐orange light (ca. 560–644 nm) and the terbium complex emitting green light (ca. 490–622 nm) upon UV irradiation. DFT calculations performed by using the DMol3 program at the BLYP/DNP level of theory revealed a nine‐coordinate structure for the lanthanide complexes.     

Metal‐Ion‐Induced Switch of Liquid‐Crystalline Orientation of Metallomacrocycles

A new series of shape‐persistent imine‐bridged macrocycles were synthesized based on dynamic covalent chemistry. The macrocycles had an alternating sequence of dibenzothiophene and N,N′‐bis(salicylidene)‐ethylenediamine (salen) tethering branched alkyl chains. The macrocycles and tetranuclear metallomacrocycles bearing long and branched alkyl chains exhibited thermotropic columnar liquid‐crystalline phases over a wide temperature range and the metallomacrocycles greatly depended on the characteristics of the coordinated metal ions. The metal‐free macrocycle showed a liquid‐crystalline phase with a lamellar structure and poor birefringence. In sharp contrast, the macrocyclic Ni complex showed a columnar oblique liquid‐crystalline phase, whereas the Pd and Cu complexes showed columnar liquid‐crystalline phases with a lamellar structure. The macroscopic organization and thermal properties of the corresponding liquid‐crystalline metallomacrocycles were significantly dependent on the subtle structural differences among the planar macrocycles, which were revealed by single‐crystal X‐ray crystallographic analysis of the macrocycles with shorter alkyl chains.     

Ordered nanostructures from self‐assembly of H‐shaped coil–rod–coil molecules

A new class of π‐conjugated, skewed H‐shaped oligomers, consisting of biphenyl, phenylene vinylene, and phenylene ethynylene units as the rigid segment, were synthesized via Sonogashira coupling and Wittig reactions. The coil segments of these molecules were composed of poly(ethylene oxide) (PEO) or PEO with lateral methyl groups between the rod and coil segment, respectively. The experimental results revealed that the lateral methyl groups attached to the surface of the rod and coil segments dramatically influenced the self‐assembling behavior of the molecules in the crystalline phase. H‐shaped rod–coil molecules containing a lateral methyl group at the surface of the rod and PEO coil segments self‐assemble into a two‐dimensional columnar or a three‐dimensional body‐centered tetragonal nanostructures in the crystalline phase, whereas molecules lacking a lateral methyl group based on the PEO coil chain self‐organize into lamellar or hexagonal perforated lamellar nanostructures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 85–92     

Helical Polyacetylene‐Based Switchable Chiral Columnar Phases: Frustrated Chain Packing and Two‐Way Shape Actuator

Chiral columns formed by a helical cis‐polyphenylacetylene (PPA) derivative P1 are reversibly switched during a phase transition between two chiral columnar phases: the frustrated Φ_h^3D‐SL phase containing four chains at low temperature and a hexagonal columnar phase Φ_h at high temperature, accompanied by a simultaneous conformational change. The helix–helix transition along the PPA backbone during the Φ_h^3D‐SL‐Φ_h transition makes the uniaxially oriented P1 capable of reversibly and reproducibly elongating (132 %) upon heating and contracting upon cooling, exhibiting the behavior of a two‐way shape actuator.     

Prismarene: An Emerging Naphthol‐Based Macrocyclic Arene

Phenol‐based macrocyclic arenes have been widely used in supramolecular chemistry, significantly enriching the toolbox of the field. In contrast, naphthol‐based macrocyclic arenes are rather underdeveloped. Very recently, Gaeta and co‐workers successfully synthesized such macrocycles (referred to as prism[n]arenes) with good guest‐binding ability by reacting 2,6‐dimethoxynaphthalene with paraformaldehyde under optimized conditions. In view of the simple synthesis and good host–guest chemistry, we anticipate that this macrocycle will find similar success and wide applications as the phenol‐based macrocyclic arenes.     

Influence of Equilibration Time in Solution on the Inclusion/Exclusion Topology Ratio of Host–Guest Complexes Probed by Ion Mobility and Collision‐Induced Dissociation

Host–guest complexes are formed by the creation of multiple noncovalent bonds between a large molecule (the host) and smaller molecule(s) or ion(s) (the guest(s)). Ion‐mobility separation coupled with mass spectrometry nowadays represents an ideal tool to assess whether the host–guest complexes, when transferred to the gas phase upon electrospray ionization, possess an exclusion or inclusion nature. Nevertheless, the influence of the solution conditions on the nature of the observed gas‐phase ions is often not considered. In the specific case of inclusion complexes, kinetic considerations must be taken into account beside thermodynamics; the guest ingression within the host cavity can be characterized by slow kinetics, which makes the complexation reaction kinetically driven on the timescale of the experiment. This is particularly the case for the cucurbituril family of macrocyclic host molecules. Herein, we selected para‐phenylenediamine and cucurbit[6]uril as a model system to demonstrate, by means of ion mobility and collision‐induced dissociation measurements, that the inclusion/exclusion topology ratio varies as a function of the equilibration time in solution prior to the electrospray process.     

Redox‐Triggered Chirality Switching and Guest‐Capture/Release with a Pillar[6]arene‐Based Molecular Universal Joint

A chiral electrochemically responsive molecular universal joint (EMUJ) was synthesized by fusing a macrocyclic pillar[6]arene (P[6]) to a ferrocene‐based side ring. A single crystal of an enantiopure EMUJ was successfully obtained, which allowed, for the first time, the definitive correlation between the absolute configuration and the circular dichroism spectrum of a P[6] derivative to be determined. The self‐inclusion and self‐exclusion conformational change of the EMUJ led to a chiroptical inversion of the P[6] moiety, which could be manipulated by both solvents and changes in temperature. The EMUJ also displayed a unique redox‐triggered reversible in/out conformational switching, corresponding to an occupation/voidance switching of the P[6] cavity, respectively. This phenomenon is an unprecedented electrochemical manipulation of the capture and release of guest molecules by supramolecular hosts.     

Synthesis,Structure, and Properties of O6‐Corona[3]arene[3]tetrazines

O₆‐Corona[3]arene[3]tetraazines, a new class of macrocyclic compounds, were synthesized efficiently in a one‐pot reaction from the nucleophilic aromatic substitution reaction between 1,4‐dihydroxybenzene derivatives and 3,6‐dichlorotetrazine in warm acetonitrile. In the crystalline structure, the resulting macrocycles adopt highly symmetric structures of a regular hexagonal cavity with all bridging oxygen atoms and tetrazine rings located on the same plane with phenylene units orthogonally orientated. The constitutional aromatic rings are able to rotate around the macrocyclic annulus, depending on the steric effect of the substituents and temperature, in solution. The electron‐deficient nature revealed by cyclic voltammetry, differential pulse voltammetry, and characteristic absorbances at a visible region show the O₆‐corona[3]arene[3]tetrazines to be suitable macrocyclic receptors for electron‐rich guests.     

Synthesis,Structure, and Properties of O6‐Corona[3]arene[3]tetrazines

O₆‐Corona[3]arene[3]tetraazines, a new class of macrocyclic compounds, were synthesized efficiently in a one‐pot reaction from the nucleophilic aromatic substitution reaction between 1,4‐dihydroxybenzene derivatives and 3,6‐dichlorotetrazine in warm acetonitrile. In the crystalline structure, the resulting macrocycles adopt highly symmetric structures of a regular hexagonal cavity with all bridging oxygen atoms and tetrazine rings located on the same plane with phenylene units orthogonally orientated. The constitutional aromatic rings are able to rotate around the macrocyclic annulus, depending on the steric effect of the substituents and temperature, in solution. The electron‐deficient nature revealed by cyclic voltammetry, differential pulse voltammetry, and characteristic absorbances at a visible region show the O₆‐corona[3]arene[3]tetrazines to be suitable macrocyclic receptors for electron‐rich guests.     

A mixed cyclodextrin‐biphenyl thermotropic liquid crystal: Synthesis,liquid‐crystalline properties,and supramolecular organization

A well‐defined structure liquid crystal heptakis [6‐deoxy‐6‐(1‐H‐1,2,3‐triazol‐4‐yl)(methyl)6‐(4‐methoxybiphenyl‐4′‐yloxy) hexanoyl]‐β‐cyclodextrin (H6B‐β‐CD) was synthesized from propargyl 6‐(4‐methoxybiphenyl‐4′‐yloxy) hexanoate (P6B) and heptakis (6‐deoxy‐6‐azido)‐β‐cyclodextrin ((N₃)₇‐β‐CD) by click reaction. The chemical structure of H6B‐β‐CD was confirmed by ¹H NMR, FTIR, and MALDI‐TOF MS. The thermal stability of the compound was investigated by thermogravimetric analysis (TGA). The liquid crystalline behavior was studied by differential scanning calorimetry (DSC), polarizing optical microcopy (POM), and wide‐angle X‐ray diffraction (WAXD) measurement. These investigations have shown that the supramolecular structure of H6B‐β‐CD are consisted of a large scale ordered lamellar structure and a small scale ordered structure (SmE) at low temperature region. As the temperature increases, the small scale structure becomes disordered relatively in the first instance, from smectic E to smectic A. Then, the lamellar structure collapses and nematic phase and isotropic phase are observed in sequence. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2838–2845, 2010     

Fluorescent Cross‐Linked Supramolecular Polymer Constructed by Orthogonal Self‐Assembly of Metal–Ligand Coordination and Host–Guest Interaction

A new host molecule consists of four terpyridine groups as the binding sites with zinc(II) ion and a copillar[5]arene incorporated in the center as a spacer to interact with guest molecule was designed and synthesized. Due to the 120 ° angle of the rigid aromatic segment, a cross‐linked dimeric hexagonal supramolecular polymer was therefore generated as the result of the orthogonal self‐assembly of metal–ligand coordination and host–guest interaction. UV/Vis spectroscopy, ¹H NMR spectroscopy, viscosity and dynamic light‐scattering techniques were employed to characterize and understand the cross‐linking process with the introduction of zinc(II) ion and guest molecule. More importantly, well‐defined morphology of the self‐assembled supramolecular structure can be tuned by altering the adding sequence of the two components, that is, the zinc(II) ion and the guest molecule. In addition, introduction of a competitive ligand suggested the dynamic nature of the supramolecular structure.     

Liquid crystalline analogues of curcumin

Compounds that are modifications of curcumin were synthesised and their mesogenic properties were studied. The central keto-enolic ring in curcumin was replaced by either a pyrazole or an isoxazole ring. This gives compounds that can form liquid crystalline phases. When two alkoxy chains are attached to the molecule, nematic and lamellar phases appear; in the case of six alkoxy chains, a hexagonal columnar phase is created. The columnar phase is constructed from columns that in the cross-section have two molecules. The pyrazole derivatives in the columnar phase preserve N–H–N hydrogen bonding.