Liquid‐Crystalline Mesogens Based on Cyclo[6]aramides: Distinctive Phase Transitions in Response to Macrocyclic Host–Guest Interactions

Producing macrocyclic mesogens that are responsive to guest encapsulation presents a significant challenge. Cyclo[6]aramides, a type of macrocycle with a hydrogen‐bond‐constrained backbone, exhibit thermotropic lamellar, discotic nematic, hexagonal, and rectangular columnar mesophases over a considerably wide temperature range, including at room temperature. Additionally, cyclo[6]aramides show unusual mesophase transitions from lamellar to hexagonal columnar phase mediated by macrocyclic host–guest (H–G) interactions between the macrocycles and alkylammonium salts. The phase transition, triggered by an organic guest engaging in H–G interactions with a macrocyclic cavity, provides a novel strategy for manipulating the properties of liquid‐crystalline materials. The crystal structure of a homologous cyclo[6]aramide reveals a disk‐shaped, near‐planar molecular backbone that facilitates intermolecular π–π stacking and leads to columnar assembly.     

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.     

Columnar Liquid Crystals from a Giant Macrocycle Mesogen

Columnar liquid crystals composed of a giant macrocyclic mesogen were prepared. The giant macrocyclic mesogen has a square hollow with a 2.5 nm diagonal, which was bounded by diindolo[3,2‐b:2′,3′‐h]carbazole (diindolocarbazole) moieties as the edges and bis(salicylidene)‐o‐phenylenediamine (salphen) moieties as the corners. The shape and size of the macrocycle were directly observed by scanning tunneling microscopy (STM). Each side of the bright square in the STM image corresponds to a diindolocarbazole moiety, and the length of the sides was consistent with the result of the single crystal analysis of diindolocarbazole. Finally, we successfully obtained a giant macrocycle with long and branched side chains, which exhibited a rectangular columnar LC phase over a wide temperature range. To the best of our knowledge, it contained the largest discrete inner space of any thermotropic columnar liquid crystal composed of macrocyclic mesogens.     

Liquid‐crystalline Metallomacrocycles Composed of Bis(hydroxypyridono)toluene Ligand and Cu2+ Ions

A series of π‐extended chelating scaffolds incorporating two hydroxypyridone moieties were synthesized. X‐ray crystallographic analysis revealed that a bis(hydroxypyridono)toluene ligand possessed a unique π‐extended structure and exhibited efficient phase segregation from the aliphatic chains attached at the heterocyclic nitrogen. The bis‐bidentate ligand formed a metal‐coordination‐induced macrocycle with Cu²⁺ ions. During the complexation, a spectral change in the visible region was induced. Furthermore, the successful development of a liquid crystal of the metallomacrocycle with appropriate side chains was achieved. Examples of liquid‐crystalline macrocycles formed via metal‐mediated self‐assembly are still rare. Among them, the macrocycle described in this paper showed an obvious hexagonal columnar phase reflecting the three‐fold symmetric planar structure of the mesogenic metal complex.     

Nonionic diethanolamide amphiphiles with unsaturated C18 hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behavior

The neat and lyotropic liquid crystalline phase behavior of three nonionic diethanolamide amphiphiles with C18 hydrocarbon chains containing one, two or three unsaturated bonds has been examined. This has allowed the effect of degree of unsaturation on the phase behavior of diethanolamide amphiphiles to be investigated. Neat linoleoyl and linolenoyl diethanolamide undergo a transition from a glassy liquid crystal to a liquid crystal at ～-85 °C, while neat oleoyl diethanolamide undergoes a transition at ～-60 °C to a liquid crystalline material before re-crystallizing at -34 °C. Oleoyl diethanolamide then undergoes a third transition from a crystalline phase to a smectic liquid crystalline phase at ～5 °C. In the absence of water, the transition temperature from a smectic liquid crystal to an isotropic liquid decreases with increasing unsaturation. The addition of water results in the formation of a lamellar phase (L(α)) for all three amphiphiles. The lamellar phase is stable under excess water conditions up to temperatures of at least 70 °C. Approximate partial binary amphiphile-water phase diagrams generated for the three unsaturated C18 amphiphiles indicate that the excess water point for each amphiphile occurs at ～60% (w/w) amphiphile.     

Thermally Driven Polymorphic Transition Prompting a Naked‐Eye‐Detectable Bending and Straightening Motion of Single Crystals

The amplification of molecular motions so that they can be detected by the naked eye (10⁷‐fold amplification from the ångström to the millimeter scale) is a challenging issue in the development of mechanical molecular devices. In this context, the perfectly ordered molecular alignment of the crystalline phase has advantages, as demonstrated by the macroscale mechanical motions of single crystals upon the photochemical transformation of molecules. In the course of our studies on thermoresponsive amphiphiles containing tetra(ethylene glycol) (TEG) moieties, we serendipitously found that thermal conformational changes of TEG units trigger a single‐crystal‐to‐single‐crystal polymorphic phase transition. The single crystal of the amphiphile undergoes bending and straightening motion during both heating and cooling processes at the phase‐transition temperatures. Thus, the thermally triggered conformational change of PEG units may have the advantage of inducing mechanical motion in bulk materials.     

SDS H2O-C4H9OH体系层状液晶的结构及增溶作用

表面活性剂溶液中关于胶束和微乳的形成及性质已有大量研究~[1]. 近年来表面活性剂分子所形成的层状液晶的结构和它的增溶. 渗透、扩散作用的研究引起了广泛的关注~[2,3,4]. 它的性质和结构的研究在实际与理论上皆有很大的意义, 特别是在生物体系中显得十分重要. 本工作利用小角度X射线衍射研究了SDS(sodium dode-cyl sulfate)-H_2O-C_4H_9OH体系层状液晶的结构及增溶C_7H_(16)后对结构的影响, 并对本体系中两亲分子在液晶中的排列和增溶的机制提出相应的看法。     

Helical arrangement of a hydrogen‐bonded columnar liquid crystal induced by a centered triphenylene derivative bearing chiral side‐chains

A hydrogen‐bonded helical columnar liquid crystal was synthesized, in which the helical structure is induced by a centered triphenylene derivative bearing chiral side‐chains. The triphenylene derivative, 2,6,10‐tris(carboxymethoxy)‐3,7,11‐tris((S)‐(‐)‐2‐methyl‐1‐butanoxy)triphenylene ( TPC4(S) ), and a dendric amphiphile, 3,5‐bis‐(3,4‐bis‐dodecyloxy‐benzyloxy)‐N‐pyridine‐4‐yl‐benzamide ( DenC12 ), were mixed in a 1:3 ratio to obtain a complex, TPC4(S)‐DenC12 . Analyses by ¹H‐NMR spectroscopy, diffusion ordered spectroscopy (DOSY), CD spectroscopy, infrared (IR) spectroscopy, polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X‐ray diffractometry revealed that TPC4(S)‐DenC12 self‐assembles to form helical columnar stacks in solution and a helical columnar liquid crystal in bulk. The hydrogen bonding between TPC4(S) and DenC12 is essential for the helical columnar organization, and the preference for a one‐handed helical conformation is likely derived from the steric interaction between the chiral side‐chains and the dendric amphiphiles in the packing of the hydrogen‐bonded columnar assemblies. Copyright © 2008 John Wiley & Sons, Ltd.     

Confinement effect on phase transitions of a discotic liquid crystal: a calorimetric study

Differential scanning calorimetry was used to investigate the confinement effects on the phase transition behaviour of a discotic liquid crystal. The liquid crystal studied is the hexa-n-octanoate of rufigallol (RHO); Millipore membranes of various pore sizes were the confining materials. The polymorphism of RHO is affected by confinement. The transition from an enantiotropic columnar phase (D1) to a monotropic columnar phase (D2) is supressed in membranes with pore sizes 500 A. The transformation from D1 to the crystalline phase is also perturbed, particularly in the membrane having an average pore size of 250 A. In the first case the crystal formed displays a double-melting endotherm, with a distinct structure melting at lower temperatures; in the other, the induction period of isothermal crystallization becomes longer and the global rate of crystallization is slowed. However, confinement shows no effect on the overall crystallization mechanism; a similar Avrami constant of n ~ 3 was obtained for both confined and bulk RHO. An analysis of the results is presented.     

Confinement effect on phase transitions of a discotic liquid crystal: a calorimetric study

Differential scanning calorimetry was used to investigate the confinement effects on the phase transition behaviour of a discotic liquid crystal. The liquid crystal studied is the hexa-n-octanoate of rufigallol (RHO); Millipore membranes of various pore sizes were the confining materials. The polymorphism of RHO is affected by confinement. The transition from an enantiotropic columnar phase (D1) to a monotropic columnar phase (D2) is supressed in membranes with pore sizes 500 A. The transformation from D1 to the crystalline phase is also perturbed, particularly in the membrane having an average pore size of 250 A. In the first case the crystal formed displays a double-melting endotherm, with a distinct structure melting at lower temperatures; in the other, the induction period of isothermal crystallization becomes longer and the global rate of crystallization is slowed. However, confinement shows no effect on the overall crystallization mechanism; a similar Avrami constant of n ~ 3 was obtained for both confined and bulk RHO. An analysis of the results is presented.     

Dynamic covalent polypeptides showing tunable secondary structures and thermoresponsiveness

Lysine‐based polypeptides can be afforded with steerable secondary structures and tunable thermoresponsiveness through dynamic covalent OEGylation. These polypeptides were formed through dynamic imine linkage via reactions of amino moieties from poly(l ‐lysine)s with aldehydes from oligoethylene glycol (OEG)‐based dendrons. In addition to solution concentrations and pH values, macromolecular effect was found to play an important role on the imine formation. OEGylated polypeptides showed characteristic thermoresponsive properties, and their phase transition temperatures were governed predominately by terminal groups and the coverage of OEG dendrons. Notably, thermally induced aggregation would enhance the imine formation even at elevated temperature. In contrast to the covalent polypeptide representatives, the dynamic covalent polypeptides conveyed different thermoresponsiveness due to imine linkages, and their phase transition temperatures could be tuned simply by varying ratios of OEG dendrons with different hydrophilicity. Furthermore, helical conformation of these polypeptides was enhanced with attachment of OEG dendrons, and could be reversibly switched through thermally induced aggregation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 33–41     

Restudy of the unusual phase behavior of the mesogen-jacketed liquid crystal polymers

1 Introduction Liquid crystals (LC) are a state of order between crystals and liquids. They have imperfect long range orders of orientation and position. Thus, they can be fluid like a liquid and they can have anisotropic prop-erties like crystals. For th…     

辛烷基苯酚聚氧乙烯醚与正癸醇层状液晶的有序性及层状结构

Order character and lamellar structure of TritonX 100/n C10H21OH/H2O lamellar liquid crystal were investigated. Partial phase diagram of TritonX 100/C10H21OH/H2O was measured at 25℃ by the polarizing microscope, and lamellar structure of the lamellar liquid crystal was verified by the 2H NMR spectra. The ESR spin probe method was used to detect the changes in the lamellar liquid crystal. A stearic acid, 5 doxylstearic acid, was used as the spin probe. The values of hyperfine coupling constant and order parameter of lamellar liquid crystal in the phase diagram were calculated. The values of the hyperfine coupling constant with different composition were almost unchanged. It indicates that the micropolarity of the lamellar liquid crystal is very similar. The order parameter decreases with the increasing water content in lamellar liquid crystal. It can be explained by considering that: First, though the penetration is determined at the given weight ratio of C10H21OH to TritonX 100, the absolute water content penetrated into the amphiphile bilayer increases with the increasing of the water content. Second, the thickness of the solvent also increases, which makes the force between layers weaker. The results also showed that order parameter of lamellar liquid crystal increased with TritonX 100 content, which may be explained from the fact that the water content penetrated into the amphiphile bilayer decreases relatively and the molecules in the amphiphile bilayer are made tighten. The interlayer spacing of lamellar liquid crystal was determined by small angle X ray diffraction. The penetration ratio of water in the lamellar liquid crystal was calculated. It was about 50%.     

油酸钠/水/十六烷/三丙烯酸季戊四醇酯体系层状 液晶的聚合

将十六烷增溶于油酸钠(NaOL)/水体系层状液晶的油层,共聚单体三丙烯酸季戊四醇酯(PETA)增溶于油酸钠/水体系层状液晶的两亲双层。72℃下,以增容于油层中的十六烷作为阻隔。在层状液晶同一两新双层内的两新分子油酸钠与共聚单体PETA之间进行共聚,得到了具有层状结构、并具有较好表面活性的共聚物。     

Synthesis and properties of mesogen‐jacketed liquid crystalline polymers containing biphenyl mesogen with asymmetric substitutions

This work focuses on the design, synthesis, and characterization of a series of mesogen‐jacketed liquid crystalline polymers (MJLCPs), poly(alkyl 4′‐(octyloxy)‐2‐vinylbiphenyl‐4‐carboxylate) (pVBP(m,8), m = 1, 2, 4, 6, 8, 10, 12). For the first time, we realized asymmetric substitutions in the mesogens of MJLCPs. The polymers obtained by conventional free radical polymerization were investigated in detail by a combination of various techniques, such as differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized light microscopy. Our results showed that all the polymers were thermally stable, and their glass transition temperatures decreased when m increased. The liquid crystalline (LC) phases that developed at high temperatures and disappeared at low temperatures were strongly dependent on the difference in lengths of alkyl groups on the 4 and 4′ substitution positions of the side‐chain biphenyl. While polymer pVBP(1,8) was not liquid crystalline, columnar liquid crystalline phases were observed for all other pVBP(m,8) (m = 2, 4, 6, 8, 10, 12) polymers. Polymer pVBP(8,8) showed a tetragonal columnar nematic liquid crystalline phase, and the other LC polymers exhibited columnar nematic phases. In additions, the smaller the difference in the lengths of the terminal alkyls, the easier the development of the liquid crystalline phase. Birefringence measurements showed that solution‐cast polymer films exhibited moderately high positive birefringence values, indicating potential applications as optical compensation films for liquid crystal displays. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Phase behavior of amphiphiles at liquid crystals/water interface: A coarse-grained molecular dynamics study

We present a coarse-grained molecular dynamics simulation study of phase behavior of amphiphilic monolayers at the liquid crystal （LC）/water interface. The results revealed that LCs at interface can influence the lateral ordering of amphiphiles. Particularly, the amphiphile tails along with perpendicularly penetrated LCs between tails undergo a two-dimension phase transition from liquid-expanded into a liquid-condensed phase as their area density at interface reaches 0.93. While, the liquid-condensed phase of the monolayer never appears at oil/water interface with isotropic shape oil particles. These findings reveal the penetration of anisotropic LC can promote ordered lateral organization of amphiphiles. Moreover, we find the phase transition point is shifted to lower surface coverage of amphiphiles when the LCs have larger affinity to the amphiphile tails.     

Effect of crystallization and liquid–liquid phase separation on phase‐separation kinetics in poly(ethylene‐co‐vinyl alcohol)/glycerol solution

Liquid–liquid thermally induced phase separation of the polymer‐diluent system of poly(ethylene‐co‐vinyl alcohol) (EVOH)‐glycerol was examined under light scattering. For EVOH with an ethylene content of 38 mol % (EVOH38), maxima of the scattered light intensity were observed that indicated that phase separation occurred by the spinodal decomposition (SD). The growth of the structures formed by the general liquid–liquid phase separation obeyed a power‐law scaling relationship in SD. For EVOH with an ethylene content of 32 mol % (EVOH32), the liquid–liquid phase separation resulted from the polymer crystallization. In this case, the structure growth showed the characteristic behavior in which the crystalline particles were initially formed, and then the droplets formed by the liquid–liquid phase separation induced by the crystallization grew rapidly. Furthermore, the growth of the droplet by the phase separation was followed by an optical microscope measurement at a constant cooling rate. The phase‐separated structure formed after the crystallization can grow faster than that formed by the normal liquid–liquid phase separation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 194–201, 2003     

Morphology of epoxy/acrylic polymer‐dispersed liquid‐crystal film in DICY thermal cure

A polymer‐dispersed liquid‐crystal (PDLC) film was prepared from UV‐curable acrylic, thermally curable epoxy, and a liquid‐crystal (LC) mixture with a fixed LC content of 40 wt %. The UV irradiation and heat treatments were in sequential steps. At first, a phase diagram of a binary mixture of LC (E63) and epoxy [diglycidyl ether of polypropylene glycol (DER736)] was established to understand their miscibility. Then, the phase‐separation temperatures and morphologies of pre‐UV‐cured films with different equivalent DER736/dicyandiamide (DICY) molar ratios were observed. Finally, the polymerization‐induced phase‐separation behavior and morphology of the PDLC film were studied by real‐time observation while the film was maintained at 130 °C under the microscope. The results showed that the acrylic network would not affect the phase‐separation behavior of the E63/DER736 mixture. In both thermally induced and polymerization‐induced phase separations, the undissolved DICY particles acted as nucleation agents and were capable of inducing E63 to separate out early. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2033–2042, 2000     

Peripheral chain length-dependent complex phase behaviour in C3-symmetric hexa-alkylated liquid crystals

We report the thermal and self-assembly properties of C₃-symmetric liquid crystalline (LC) molecules consisting of a conformationally tunable triazole-based mesogen and six-fold alkyl chains. Unlike the LC compound (1) based on non-crystallisable octyl chains, 2 and 3, which have crystallisable dodecyl and tetradecyl chains, respectively, exhibit a cold crystallisation which only takes place under slow heating conditions (2°C/min). In contrast with the vertically interdigitated lamellar crystalline phase of 1, a laterally interdigitated bilayered lamellar structure driven by the crystallisation of the dodecyl or tetradecyl chains is observed in the cold crystallisation temperature range. In addition to their crystalline morphology, 2 and 3 show LC morphological behaviour distinct from that of 1, 2 and 3 exhibit a hexagonal columnar LC phase consisting of T-shaped conformers rather than the lamellar LC phase of 1. The morphological transformation from the lamellar (1) to the columnar phase (2 and 3) can be rationalised by the alleviation of the conformational energy of the longer alkyl chains. Consequently, the simple variation of alkyl chain length in the C₃-symmetric LC system results in contrasting thermal and assembly properties in the crystalline and LC phases.     

Remote Control of the Planar Chirality in Peptide‐Bound Metallomacrocycles and Dynamic‐to‐Static Planar Chirality Control Triggered by Solvent‐Induced 310‐to‐α‐Helix Transitions

The dynamic planar chirality in a peptide‐bound Ni^II‐salphen‐based macrocycle can be remotely controlled. First, a right‐handed (P)‐3₁₀‐helix is induced in the dynamic helical oligopeptides by a chiral amino acid residue far from the macrocyclic framework. The induced planar chirality remains dynamic in chloroform and acetonitrile, but is almost completely locked in fluoroalcohols as a result of the solvent‐induced transition of the peptide chains from a 3₁₀‐helix to a wider α‐helix, which freezes the rotation of the pendant peptide units around the macrocycle.