Hexagonal Columnar Liquid Crystalline Phase Research Articles

Electro-Optic Switching by Helicene Liquid Crystals

Binary mixtures of the aggregating helicene 1 with dodecane have, at dodecane concentrations >30 vol %, a nematic liquid crystalline phase and, at dodecane concentrations ≲5 vol %, a hexagonal columnar liquid crystalline phase. The helical structure with donor and acceptor groups at opposite ends gives rise to a molecular dipole moment that is parallel to the helix axis and a positive dielectric anisotropy. Accordingly, the helix axes orient parallel to an applied electric field, providing the basis for electro-optic switching.

Self-Assembly-Induced Supramolecular Hexagonal Columnar Liquid Crystalline Phase Using Laterally Attached Nonmesogenic Templates

A novel poly[di(4-heptyl) vinylterephthalate] has been synthesized based upon a free radical polymerzation from a newly designed monomer having a nonmesogenic template with two double-swallow-tailed 4-heptyl (Y-shaped) groups. The resulting polymer consists of a polyethylene backbone and a 2,5-bis(4-heptyloxycarbonyl)phenyl lateral substitutent on every second carbon atom of the backbone. Although neither the backbone nor the pendent template exhibits liquid crystalline (LC) behavior, they couple together to form a supramolecular hexagonal columnar LC phase on a scale of greater than 1.5 nm in the polymer. Therefore, it is deduced that this supramolecular LC structure is constructed via a cooperative assembly of a helical arrangement of the backbones with the pendent templates.

Mechanistic Investigations on the Formation of Supramolecular Cylindrical Shaped Oligomers and Polymers by Living Ring Opening Metathesis Polymerization of a 7-Oxanorbornene Monomer Substituted with Two Tapered Monodendrons

The synthesis of the monomer exo,exo-5,6-bis[[[(3,4,5-tris((4-(dodecyl-1-oxy)benzyl)oxy)]benzyl)oxy]carbonyl]-7-oxabicyclo[2.2.1]hept-2-ene (4), containing two tapered monodendrons and its living ring-opening metathesis polymerization initiated with RuCl2(CHPh)(PCy3)2 are discussed. Oligomers and polymers with narrow molecular weight distribution (Mw/Mn = 1.06−1.29) and degrees of polymerization (DP) from 6 to 120, which correspond to Mn from 12 600 to 252 800, were synthesized and characterized. The monomer (4) and the corresponding polymers (5) self-assemble into disklike and cylindrical shapes which produce an enantiotropic hexagonal columnar (Φh) liquid crystalline (LC) phase. The analysis of the Φh phase of the monomer, oligomers, and polymers as a function of the DP reveals four regions and mechanisms for the generation of the Φh phase, i.e., below the DP which forms a disklike molecule, below the DP which corresponds to the maximum length of a disklike molecule (DP = 26), up to the DP which corresp...

Columnar Liquid Crystals from Shape‐Persistent Dendritic Molecules

The molecular geometry is mirrored in the macroscopically ordered patterns found in a series of stiff, phenylacetylene dendrimers 1. These compounds form hexagonal columnar liquid crystalline phase with snowflake-like morphologies.

Self-assembly of twin tapered bisamides into supramolecular columns exhibiting hexagonal columnar mesophases. Structural evidence for a microsegregated model of the supramolecular column

Abstract The 1,2-bis[3,4,5-tris(alkan-1-yloxy)benzamido] ethanes (DA-n , where n is the number of carbons in the alkanyl group) form a high temperature hexagonal columnar (ϕh) liquid crystalline phase when n ' 10, 11, 12, 14, 16 and 18. DA-n with n ' 4, 5, 6, and 7 show at elevated temperatures a distorted hexagonal crystal phase. X-ray diffraction data support a model for the ϕh phase consisting of a 2-D hexagonal lattice of self-assembled supramolecular columns in which the melted outstretching alkyl chains of DA-n occupy a space of constant density surrounding a rigid amide channel. A local ABAB stacking of layers along the column is proposed. Each layer contains two DA-n molecules. Layer B is rotated by 90[ddot] around the column axis relative to layer A. H-bonding between the amide groups is responsible for this mode of self-assembly.

Fluorophobic Effect Induces the Self-Assembly of Semifluorinated Tapered Monodendrons Containing Crown Ethers into Supramolecular Columnar Dendrimers Which Exhibit a Homeotropic Hexagonal Columnar Liquid Crystalline Phase

The rational design, synthesis, and characterization of the building blocks obtained by the esterification of the first generation of tapered monodendrons 3,4,5-tris(p-dodecan-1-yloxy)benzoic acid (12-AG) and 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzoic acid (12-ABG) containing semifluorinated dodecyl groups [i.e., 12Fn-AG-15C5 (n = 0, 4, 6, 8), 12Fn-AG-B15C5, 12Fn-ABG-15C5, and 12Fn-ABG-B15C5 (n = 0 and 8) where n following the letter F represents the number of outer perfluorinated methylenic units of the dodecyl group] with 4‘-hydroxymethyl(benzo-15-crown-5) (B15C5) and 1-hydroxymethyl(15-crown-5) (15C5) are described. All building blocks self-assemble into supramolecular cylindrical or rod-like dendrimers via ion-mediated complexation processes. These rod-like supermolecules form a thermotropic hexagonal columnar (Φh) liquid crystalline (LC) phase. The fluorination of the dodecyl groups of these tapered building blocks enhances dramatically their self-assembly ability. The building blocks based on n = 6 and 8 self-assemble into supramolecular columns solely via the fluorophobic effect. Direct structural characterization of the supramolecular columns obtained via these two molecular recognition processes by a combination of techniques consisting of differential scanning calorimetry, X-ray diffraction, and thermal optical polarized microscopy, and of the columns obtained solely via the fluorophobic effect allowed the construction of molecular models for the supramolecular columns obtained via these two organizing forces. An increase in the column diameter with increasing n and with the complexation of metal salts (i.e., alkali metal trifluoromethanesulfonates) accounts for a structural model in which the uncomplexed and complexed crown ethers are placed side-by-side in the center of the column with the melted tapered side groups radiating toward its periphery. The perfluorinated segments of the building blocks are microsegregated from the perhydrogenated and aromatic segments of the column. The supramolecular columns obtained from building blocks with n = 8 align homeotropically in the Φh LC phase on untreated glass slides, i.e., form single crystal liquid crystals in which the long axes of their columns are perpendicular to the glass surface. Both the self-assembly of supramolecular columns induced solely by the fluorophobic effect and the homeotropic alignment of these columns in their Φh LC phase open extremely interesting new synthetic and technologic opportunities in the area of self-assembly of well-defined supramolecular architectures obtained from monodendrons and other building blocks.

Tubular Architectures from Polymers with Tapered Side Groups. Assembly of Side Groupsviaa Rigid Helical Chain Conformation and Flexible Helical Chain Conformation InducedviaAssembly of Side Groups

Syntheses of N-[3,4,5-tris(n-dodecan-1-yloxy)phenyl]maleimide (6) and exo,exo-5,6-bis[[[3,4,5-tris(n-dodecan-1-yloxy)benzoyl]oxy]methyl]-7-oxabicyclo[2.2.1]hept-2-ene (16) and their polymerization by radical, anionic and ring opening metathesis polymerizations, respectively, to yield the corresponding polymers 7 and 17 are described. Regardless of the polymerization method by which it was synthesized, 7 produced a hexagonal columnar (Φh) liquid crystalline phase generated from the tubular architecture of the rigid 7/2 helical chain conformation surrounded by its tapered side groups. 17 also produces a Φh phase. However, in this case, the assembly of tapered side groups of 17 into a tubular architecture induced a 3/1 helical chain conformation of its own flexible backbone. These two experiments support the model in which polymers containing tapered side groups form tubular supramolecular architectures by inducing a flexible helical chain conformation during the self-assembly of their own tapered side group...

Molecular design of amphitropic liquid crystalline carbohydrates–amphiphilic N-methyl-glucamides exhibiting lamellar, columnar or cubic mesophases

Amphiphilic 1-deoxy-1-(N-methylbenzamido)-D-glucitols display smectic, hexagonal columnar or discontinuous cubic thermotropic liquid crystalline phases depending on the number of alkyl chains attached to the benzamido group.

Supramolecular Tubular Structures of a Polymethacrylate with Tapered Side Groups in Aligned Hexagonal Phases

X-ray methods have been used to analyze the supramolecular tubular structures in the hexagonal solid state and columnar hexagonal liquid crystalline (O h ) phases of a polymethacrylate with tapered side groups: specifically, poly{2-{2-[2-(2-(methacryloyloxy)ethoxy)ethoxy]ethoxy)}ethyl 3,4,5-tris((p-(dodecyloxy)-benzyl)oxy)benzoate}, abbreviated as 12-ABG-4EO-PMA. Oriented fibers were drawn from the O h liquid crystalline phase at ∼ 60°C and annealed for several days at 4°C. The X-ray pattern for these fibers recorded at room temperature (25°C) contained eight equatorial reflections that are orders predicted for a hexagonal unit cell with a= b= 60.4 A