Columnar Liquid Crystal Phase Research Articles

Liquid Crystal Ordering and Isotropic Gelation in Solutions of Four-Base-Long DNA Oligomers.

Liquid crystal ordering is reported in aqueous solutions of the oligomer 5'-ATTAp-3' and of the oligomer 5'-GCCGp-3'. In both systems, we quantitatively interpret ordering as stemming from the chaining of molecules via a "running-bond" type of pairing, a self-assembly process distinct from the duplex aggregation previously reported for longer oligonucleotides. While concentrated solutions of 5'-ATTAp-3' show only a columnar liquid crystal phase, solutions of 5'-GCCGp-3' display a rich phase diagram, featuring a chiral nematic phase analogous to those observed in solutions of longer oligonucleotides and two unconventional phases, a columnar crystal and, at high concentration, an isotropic amorphous gel. The appearance of these phases, which can be interpreted on the basis of features of 5'-GCCGp-3'molecular structure, suggests distinctive assembly motifs specific to ultrashort oligonucleotides.

Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase.

Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements. Columnar-stacked V-shaped carbon frameworks display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive.

Highly Ordered Rectangular Columnar Ionic Liquid Crystals: A More Efficient Medium for Intramolecular Diels Alder Reactions

AbstractHerein, we present the synthesis, the thermal and mesophormic properties of trialkyl(1,3,5‐benzene)trisimidazolium salts. These salts form highly ordered rectangular columnar ionic liquid crystal phases and can be used as reaction media for Diels Alder reactions. The use of the ionic liquid crystal phase favours the formation of the intramolecular Diels Alder products, even in high concentration reaction conditions. We show that the ionic liquid crystal phase can be recycled and reused as solvent for at least 10 times, without any loss of yield or selectivity in the Diels Alder reaction.

Polycatenar Mesogens with Various Degree of Flexibility of Molecular Structure

A series of newly synthesised rod-like polycatenar mesogens forms columnar phases, with the number of molecules in the column cross section depending on the core rigidity. For non-symmetric molecules, an additional density modulation, namely helical arrangement of molecules with a periodicity of approximately 10 molecular distances develops along the columns. For one of the compounds, a new type of columnar liquid crystal phase with 3D positional order is observed. Introducing a stilbene unit in the mesogenic core enhances the fluorescent properties of the compounds. In the hexagonal columnar phase, polarised light emission is observed.

Self-Assembled Hierarchical Superstructures from the Benzene-1,3,5-Tricarboxamide Supramolecules for the Fabrication of Remote-Controllable Actuating and Rewritable Films.

The well-defined hierarchical superstructures constructed by the self-assembly of programmed supramolecules can be organized for the fabrication of remote-controllable actuating and rewritable films. To realize this concept, we newly designed and synthesized a benzene-1,3,5-tricarboxamide (BTA) derivative (abbreviated as BTA-3AZO) containing photoresponsive azobenzene (AZO) mesogens on the periphery of the BTA core. BTA-3AZO was first self-assembled to nanocolumns mainly driven by the intermolecular hydrogen-bonds between BTA cores, and these self-assembled nanocolumns were further self-organized laterally to form the low-ordered hexagonal columnar liquid crystal (LC) phase below the isotropization temperature. Upon cooling, a lamello-columnar crystal phase emerged at room temperature via a highly ordered lamello-columnar LC phase. The three-dimensional (3D) organogel networks consisted of fibrous and lamellar superstructures were fabricated in the BTA-3AZO cyclohexane-methanol solutions. By tuning the wavelength of light, the shape and color of the 3D networked thin films were remote-controlled by the conformational changes of azobenzene moieties in the BTA-3AZO. The demonstrations of remote-controllable 3D actuating and rewritable films with the self-assembled hierarchical BTA-3AZO thin films can be stepping stones for the advanced flexible optoelectronic devices.

Influence of Proton and Salt Concentration on the Chromonic Liquid Crystal Phase Diagram of Disodium Cromoglycate Solutions: Prospects and Limitations of a Host for DNA Nanostructures.

Lyotropic chromonic liquid crystals have recently been suggested for use as a self-organized host for dispersing and aligning self-organized DNA origami nanostructures. However, an appropriate pH value and a suitable cation concentration are necessary to stabilize such nanostructures and to avoid unfolding of the DNA. The present study shows that the nematic and columnar liquid crystal phases appearing in aqueous solutions of disodium cromoglycate are robust against the replacement of deionized water by a neutral or alkaline buffer solution. However, disodium cromoglycate precipitates when an acidic buffer is used or when the concentration of magnesium cations exceeds a critical concentration of about 0.6-0.7 mmol/L.

Supramolecular Columnar Liquid Crystals with Tapered-Shape Simple Pyrazoles Obtained by Efficient Henry/Michael Reactions.

A straightforward synthesis of mesogenic pyrazoles starting from benzaldehydes by a combination of efficient Henry and Michael reactions led to novel supramolecular liquid crystals. The mesogens are fluorescent 3,5-dimethyl-4-(di or trialkoxyphenyl)pyrazoles and, in spite of the tapered shape of these molecules and their structural simplicity (only one phenyl ring), columnar liquid-crystal phases were formed that are stable at room temperature. The self-assembled structure was studied by XRD and the columnar cross section contains two molecules on average with an antiparallel arrangement of pyrazoles interacting through hydrogen bonds. In contrast, the single-crystal structure of a trimethoxy analog did not show hydrogen-bonded pyrazoles but chains of head-to-tail arranged molecules.

A liquid-crystalline hexagonal columnar phase in highly-dilute suspensions of imogolite nanotubes.

Liquid crystals have found wide applications in many fields ranging from detergents to information displays and they are also increasingly being used in the ‘bottom-up' self-assembly approach of material nano-structuration. Moreover, liquid-crystalline organizations are frequently observed by biologists. Here we show that one of the four major lyotropic liquid-crystal phases, the columnar one, is much more stable on dilution than reported so far in literature. Indeed, aqueous suspensions of imogolite nanotubes, at low ionic strength, display the columnar liquid-crystal phase at volume fractions as low as ∼0.2%. Consequently, due to its low visco-elasticity, this columnar phase is easily aligned in an alternating current electric field, in contrast with usual columnar liquid-crystal phases. These findings should have important implications for the statistical physics of the suspensions of charged rods and could also be exploited in materials science to prepare ordered nanocomposites and in biophysics to better understand solutions of rod-like biopolymers.

Molecular dynamics of anhydrous glycolipid self-assembly in lamellar and hexagonal phases.

The molecular dynamics of a synthetic branched chain glycolipid, 2-decyl-tetradecyl-β-d-maltoside (C14-10G2), in the dry assemblage of smectic and columnar liquid crystal phases has been studied by dielectric spectroscopy as a function of frequency and temperature during the cooling process. Strong relaxation modes were observed corresponding to the tilted smectic and columnar phases, respectively. At low frequency (∼900 Hz to 1 kHz) in the smectic phase, Process I* was observed due to the tilted sugar bilayer structure. The process continued in the columnar phase (Process I) with an abrupt dynamic change due to phase transition in the frequency range of ∼1.3 kHz to 22 kHz. An additional process (Process II) was observed in the columnar phase with a broader relaxation in the frequency range of ∼10 Hz to 1 kHz. A bias field dependence study was performed in the columnar phase and we found that the relaxation strength rapidly decreased with increased applied dc bias field. This relaxation originates from a collective motion of polar groups within the columns. The results of dielectric spectroscopy were supported by a molecular dynamics simulation study to identify the origin of the relaxation processes, which could be related to the chirality and hydrogen bonds of the sugar lipid.

Anthra- and pentacenequinone derivatives: influence of structure on the formation of columnar liquid crystal phases

The mesomorphic properties of novel acenequinones reveals that a perpendicular packing motif is an important factor for determining mesophase stability.

Origin of the High Carrier Mobilities of Nonperipheral Octahexyl Substituted Phthalocyanine

The carrier transport properties of nonperipheral octahexyl substituted phthalocyanine H2Pc(C6H13)8np in its crystal and columnar (Col) liquid crystal (LC) phase were investigated using density functional theory (DFT) calculations in combination with molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. In the crystal phase, we found that the nonperipherally substituted chains of H2Pc(C6H13)8np, that interpenetrate adjacent phthalocyanines (Pcs), significantly alter the Pc-core stacking such that higher hole mobilities are observed for this system than for the nonsubstituted H2Pc. This chain interpenetration was found to be inherited by the column stacking in the Col phase and hindered the Pc-core in-plane rotations between adjacent Pcs. This rotational hindrance further caused a nonuniform distribution of the adjacent dimer Pc-core in-plane orientation configurations. The relatively high carrier mobility in the Col phase in this system can be rationalized by the nonuniform distribution of the dimer configurations that give relatively high electronic coupling between the adjacent dimers. Our results show the remarkable effects of nonperipheral substitutions on the carrier transport properties in both the crystal and Col LC phases.

Evidence of liquid crystal-assisted abiotic ligation of nucleic acids.

The emergence of early life must have been marked by the appearance in the prebiotic era of complex molecular structures and systems, motivating the investigation of conditions that could not only facilitate appropriate chemical synthesis, but also provide the mechanisms of molecular selection and structural templating necessary to pilot the complexification toward specific molecular patterns. We recently proposed and demonstrated that these functions could be afforded by the spontaneous ordering of ultrashort nucleic acids oligomers into Liquid Crystal (LC) phases. In such supramolecular assemblies, duplex-forming oligomers are held in average end-to-end contact to form chemically discontinuous but physically continuous double helices. Using blunt ended duplexes, we found that LC formation could both provide molecular selection mechanisms and boost inter-oligomer ligation. This paper provides an essential extension to this notion by investigating the catalytic effects of LC ordering in duplexes with mutually interacting overhangs. Specifically, we studied the influence of LC ordering of 5'-hydroxy-3'-phosphate partially self-complementary DNA 14mers with 3'-CG sticky-ends, on the efficiency of non-enzymatic ligation reaction induced by water-soluble carbodiimide EDC as condensing agent. We investigated the ligation products in mixtures of DNA with poly-ethylene glycol (PEG) at three PEG concentrations at which the system phase separates creating DNA-rich droplets that organize into isotropic, nematic LC and columnar LC phases. We observe remarkable LC-enhanced chain lengthening, and we demonstrate that such lengthening effectively promotes and stabilizes LC domains, providing the kernel of a positive feedback cycle by which LC ordering promotes elongation, in turn stabilizing the LC ordering.

New Advances in the One-Dimensional Coordination Polymer Copper(II) Alkanoates Series: Monotropic Polymorphism and Mesomorphism

The polymorphism in the copper(II) alkanoates, recently discovered for one member, has been thoroughly studied for the whole series, from 3 to 16 C atoms. Three polymorphic phases have been found, all of them sharing the same molecular unit, the paddle-wheel, which grows forming a 1D coordination polymer or catena. The three polymorphs are defined by a different packing of these catenae and a specific arrangement of the alkyl chains. Ten new crystal structures of those compounds have been solved by high resolution powder diffraction and presented in this paper. The polymorphism in this series has been found to be monotropic and is responsible for the complex thermal behavior observed. The most characteristic feature, the endothermic–exothermic effect, has been explained for the first time in these compounds by a combination of data from differential scanning calorimetry (in normal and modulated modes), powder X-ray diffraction and Fourier transform infrared spectroscopy. These techniques, together with small-angle X-ray scattering and optical microscopy, were used to analyze the hexagonal columnar discotic liquid crystal phase of copper(II) alkanoates. Thus, new information has been found in the packing and stacking of the discs formed by the paddle-wheel units, also maintained in the mesophase.

Hierarchical Striped Walls Constructed by the Photopolymerization of Discotic Reactive Building Blocks in the Anisotropic Liquid Crystal Solvents

A triphenylene-based reactive mesogenic molecule (abbreviated as HABET) was newly designed and synthesized as a programmed building block to construct the striped walls by the photopolymerization in the anisotropic liquid crystal (LC) solvents. On the basis of thermal, scattering and microscopic analyses, it was found that HABET formed three ordered structures: a columnar hexagonal LC phase (ΦH), a tilted columnar hexagonal LC phase (ΦT) and a highly ordered columnar oblique crystal phase (ΦOK). The microscopic molecular orientations in the hierarchical superstructures were controlled in the anisotropic LC solvents with the help of surface anchoring forces, while the dimensions of the striped wall morphologies were determined by the patterned photomasks. The long axis of self-assembled columns in the striped walls was perpendicular to the surface alignment direction regardless of the photomask direction. Additionally, it was realized that the shapes of water drops as well as the surface water contact angles can be tuned by the hierarchical superstructures and morphologies of the polymerized HABET networks. The anisotropic hierarchical superstructures and morphologies concurrently fabricated during the polymerization in the anisotropic LC medium can offer a potential pathway for liquid transportation in the microfluidic devices.

Lateral extension induces columnar mesomorphism in crucifix shaped quinoxalinophenanthrophenazines

Reported here is the columnar mesomorphism of board shaped dyes based on quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (TQPP) derivatives that was induced by an increase in lateral bulk. TQPP derivatives with protons, tert-butyl and 4-tert-butyl-phenyl groups in positions 2 and 11 are compared, as well as dodecylthio, dodecyloxy, phytanylthio, and phytanyloxy side-chains. Only derivatives with 4-tert-butyl-phenyl groups display columnar liquid crystal phases over wide ranges of temperature while all other TQPPs are not liquid crystalline except for the compound with tert-butyl groups and phytanyloxy side-chains that shows a Colr mesophase over a temperature range of 26 °C. The sole attachment of phytanyl groups does not effectively induce columnar mesophases. However, the lateral attachment of bulky groups to the TQPP core induces columnar mesomorphism because of the in-plane aspect ratio decrease and the favored twisted or helical π-stacking of the molecules in columns rather than the parallel co-planar packing.

Folded discotic dimers.

We report the synthesis and properties of a dibenzophenazine discotic dimer, which was found to adopt a folded conformation in solution. This stable π-stacked structure persists at elevated temperatures and in all solvents examined. Folding allows the dimer to assemble into a columnar liquid crystal phase, despite its short linking group.

Smectic assemblies in C₃-symmetric hexa-alkylated liquid crystals: transformation from smectogen to discogen via hydrogen bonding.

In this paper, we report a C3-symmetric liquid crystal (LC) with sixfold alkyl peripheries exhibiting an unusual smectic E-like organization in the LC state. Based on conformational considerations, the smectic assembly is attributed to the formation of an endo-type Y conformer of asymmetric triazolyl and benzylic groups that cannot be accessed in other C3-symmetric molecules exclusively showing columnar assemblies. The Y conformers form a two-dimensional oblique lattice in the aromatic layers of the ordered smectic phase. In addition, the Y-shaped molecule in the smectic phases can change into a circular shape by the 1 : 1 hydrogen-bonding interaction with a gallic acid derivative, which leads to a hexagonal columnar LC phase. The triazole-based LC design concept proves the smectic LC assembly in the C3-symmetric system, and provides the supramolecular manipulation of LC morphologies.

SAXS reveals the magnetic alignment pathway of the goethite columnar liquid crystal phase

The alignment of board-like colloidal goethite particles in the dense rectangular centred columnar liquid crystal phase in an external magnetic field is studied using small angle X-ray scattering (SAXS). Transient SAXS-patterns show broadening of the columnar reflections in specific directions. While the reflections along the field stay at a constant Q-value, the other reflections do not. These results imply a certain pathway of reorientation. It appears that alignment proceeds via collective rotation of domains inducing ‘nanoshear’ between the layers of particles, which slide over each other. The results support the recently suggested martensitic transition pathway for the simple and centred rectangular columnar phases, which were found to spontaneously transform into each other in another goethite system. The results also provide a fine example of how SAXS can be used to study reorientation behaviour of liquid crystals at the nanoscale.

Self-organisation properties of homomeric dipeptides derived from valine

Three optically active liquid crystal (LC) homomeric dipeptides, in particular, a pair of enantiomers and a diastereomer formed by joining two half-disc-like entities through a dipeptide spacer comprising L-L, D-D and L-D valine residues, have been synthesised and characterised. Hydrogen-bond-directed self-assembly of these non-discoid supramolecules results in the formation columnar (Col) LC phase. They form a stable organo gel in polar organic solvents through intermolecular hydrogen bond, and their scanning electronic microscopy (SEM) images reveal the presence of entangled network. The interaction of these homomeric dipeptides with nanaoparticles (silica species) has also been investigated by SEM images and UV-visible experiments.

Homeotropic Alignment of Lyotropic Chromonic Liquid Crystals Using Noncovalent Interactions

We report on the homeotropic alignment of lyotropic chromonic liquid crystals (LCLCs). Homeotropic anchoring of LCLCs is difficult to achieve, and this challenge has limited development of applications for LCLCs. In this work, homeotropic alignment is achieved using noncovalent interactions between the LCLC molecules and various alignment layers including graphene, parylene films, poly(methyl methacrylate) films, and fluoropolymer films. The LCLC molecules are unique in that they self-assemble via noncovalent interactions in water into elongated aggregates which, in turn, form nematic and columnar liquid crystal (LC) phases. Here we exploit these same noncovalent interactions to induce homeotropic anchoring of the nematic LCLC. Homeotropic alignment is confirmed by polarized optical microscopy and conoscopy. We also report on novel transient stripe textures that occur when an initial flow-induced planar alignment transforms into the equilibrium homeotropic alignment required by boundary conditions. An understanding of this behavior could be important for switching applications.