Preparation of Stable Anisotropic Films with Columnar Order from Polymerizable Star-shaped Supramolecular Liquid Crystals

We have fabricated new stable anisotropic films with columnar order using star-shaped supramolecular liquid crystals as photoreactive monomers. The polymerizable supramolecular liquid crystal exhibiting a hexagonal columnar mesophase has been prepared simply through hydrogen bonding between a phloroglucinol core and pyridine derivatives containing acrylate groups in the alkyl chain. Photopolymerization of the supramolecular monomer in the liquid crystalline state yielded cross-linked anisotropic polymer networks with columnar order. The controlled approach in the present study opens a new way to design and prepare stable anisotropic materials for potential electronic and optical applications.     

Liquid Crystals arrive back home at their birthplace

The preparation and characterisation of a series of hydrogen bonded liquid crystalline dimers containing benzoic acid, alkanoic acid and phenol donors and alkoxy-stilbazole or alkoxy-4-pyridone hydrogen bond acceptors are reported. These heterodimers possess strong intermolecular donor–acceptor hydrogen bonding. The heterodimers, as well some of the individual components used in their preparation, possess liquid crystalline phases.     

Novel cyclotriveratrylene columnar liquid crystal with three alkyl chains: The balance between the number and length of alkyl chains for liquid crystalline behavior

Series of cyclotriveratrylene (CTV) derivatives with triazole ring and three alkyl groups were prepared by one-pot click condensation in yield of 80–88%. The structures and crown conformations were confirmed by NMR and MS. Their liquid crystalline properties were investigated by DSC, POM and XRD analysis. The studies on mesomorphic properties suggested that the CTV derivatives with pentyl, hexyl or dodecyl groups show no mesophase but the one with octadecyl groups possesses ordered hexagonal columnar mesophase. In comparison with the reported columnar CTV liquid crystals with six alkyl chains at least, the CTV columnar CTV liquid crystal with three alkyl chains was reported for the first time. These results suggested a subtle balance between the number and length of alkyl chains for columnar CTV liquid crystalline behavior.     

Design,Synthesis and Analysis of Chlorohydroquinone Derivatives—Liquid Crystalline Complexes

A novel linear double hydrogen-bonded liquid crystalline material is designed and isolated. The ingredients of the mesogens synthesized are chloro hydroquinone (ClHQ) and p-n alkyloxy benzoic acid (nBAO) where n varied from pentyl to dodecyl alkyloxy carbon numbers. The series is abbreviated as ClHQ + nBAO, and seven of eight synthesized complexes are found to exhibit liquid crystalline phases. These liquid crystalline complexes are characterized by Fourier Transformation Infrared spectroscopy (FTIR) in order to confirm the formation of hydrogen bond. Mesophases and their corresponding transition temperatures are studied by polarizing optical microscopy (POM) and their respective enthalpy values along with the order of the transitions are determined by Differential Scanning Calorimetry (DSC). The experimental measurement of tilt angle is carried out by optical extinction method and fitted to the theoretically predicted mean field exponent which is found to be in good agreement. Dielectric relaxations at different temperatures in nematic phase for the complexes have been carried out and their corresponding activation energy values are calculated from Cole–Davidson plots. Light filtering action in the liquid crystalline complexes is done to validate the commercial applications of these mesogens.     

Polymorphic Modifications of Chitosan

This work describes the analysis of the crystal structures of chitosan, its main polymorphic modifications, and its characteristic mutual chain packing and hydrogen bond systems in the crystalline regions of conformers. The analysis takes into consideration the crystal structures of chitosan complexes (salts) with organic and inorganic acids and their structural transformations. Notably, the transformation of the hydrated form of chitosan into anhydrous is found to be irreversible and occurs either at high temperatures or through a less stable form of hydrated salts. The interaction with polyanions during the formation of multilayer films can be considered as a way to form the anhydrous crystalline form of chitosan.     

Experimental evidence for extended hydrogen diffusion in silicon thin films during light-soaking

We have used mass spectrometry to detect hydrogen effusing from silicon thin films exposed to light. Our results indicate a long range diffusion of hydrogen through the whole film, which ends with its release into the vacuum system. The changes in the film properties are characterized by dark and photoconductivity and hydrogen exodiffusion measurements. From the evolution of dark conductivity measurements after turning off the light, we show that this long range motion of hydrogen is not due to the heating of the sample. A comparison of hydrogen exodiffusion spectra of as-deposited and light-soaked samples shows that the weakly-bonded hydrogen content decreases by 30% for a-Si:H films and that the tightly-bonded hydrogen migrates to grain boundaries of crystalline regions in the case of pm-Si:H films. These results clearly demonstrate the long range motion of hydrogen during light soaking.     

Synthesis of novel azoester homologous series of liquid crystalline behavior and the study of mesomorphism dependence on lateral substitution of middle phenyl ring

The titled azoester liquid crystalline homologous series consists of eleven homologues. The pentyl to tetradecyl derivatives of the series are nematogenic without exhibition of smectogenic character. Rest of the members of the series are nonliquid crystalline in nature. Textures of the nematic mesophase are schlieren or threaded type. Transition curves in the phase diagram showed normal phase behavior. Transition temperatures and liquid crystal behavior observed under an optical polarizing microscope equipped with a heating stage. An odd even effect is observed for nematic-isotropic transition curve. Analytical and spectral data confirms the structures of the molecules. Present homologous series is predominant nematogenic and partly nonmesogenic. Average thermal stability for nematic is 125.33°C and nematogenic mesophase length varies between 12°C to 48°C at tetradecyl (C₁₄) and octyl (C₈) derivatives, respectively.     

Multirings Aromatic Aldehyde Liquid Crystal with Azo Linkage and Their Photosensitivity in Mesophase

Ten new rod-like aromatic aldehyde liquid crystalline molecules with azo linkage were synthesized, in which bi(trans-cyclohexyl), cyclohexyl phenyl, and biphenyl carboxylic acid mesogenic cores with terminal ethyl, n-propyl, n-butyl, and n-pentyl substituents were esterified with azo benzoic aldehyde. These molecules were designed in an attempt to construct a series of new azo liquid crystalline molecules to investigate the influence of ultraviolet (UV) light on their mesophase. All compounds have been characterized on the basis of their spectral data, differential scanning calorimeter (DSC), and hot stage polarizing optical microscope (HS-POM). All these compounds exhibited liquid crystalline phase that belonged to nematic and photosensitive properties. Their temperature ranges of mesophase are from 101 °C to 150 °C. Under irradiated 365 nm UV light, they showed photosensitivity in the solvent of methanol. Observed under HS-POM, the UV light also did change the textures of these compounds. The result showed that terminal ethyl is enough for these molecules to exhibit wider temperature range of mesophase, and these new molecules have photosensitivities observed under illumination of UV light not only in solution but also in mesophase due to the change of their structures from trans isomer to cis one.     

“Molecular Rope Curtain” Type of Liquid Crystals Based on a Sliding Graft Copolymer Having Mobile PEG Side Chains

A sliding graft copolymer having a polyrotaxane main chain and side chains of polyethylene glycol with a molecular weight of 2000 (PEG2000) was found to be a novel “molecular rope curtain” type of liquid crystalline material, which displayed a smectic A mesophase between 51 °C and 250 °C without any rigid mesogenic moieties.     

Synthesis of liquid crystals based on hydrogen-bonding of 4-(Octyloxy)benzoic acid with 4-alkylbenzoic acids

A molecular recognition process has been used to form new mesogenic molecular structures, where intermolecular hydrogen bonding occurs between 4-(octyloxy)benzoic acid (8BAO) and four 4-alkylbenzoic acids (nBAs, n = 2, 5, 6, 7). The synthesis of these complexes has been attained by resorting to mechanochemistry. The resulting materials have been characterized by polarizing optical thermal microscopy, differential scanning calorimetry, vibrational spectroscopy, X-ray powder diffraction, and ¹H NMR relaxometry. All the elements of the series show the formation of a mesophase. For one of the complexes, its electro-optical properties have also been assessed, resulting comparable to those of other widely used liquid crystals.     

Design,synthesis and characterization of hydrogen bonded liquid crystals formed between methyl malonic acid and p-n-alkyloxy/alkyl benzoic acids

Two novel homologous series of hydrogen bonded liquid crystals (HBLC) comprising of 14 mesogens are formed between Methyl Malonic acid (MM) and p-n-alkyloxy/alkyl benzoic acids (nBAO/nBA). FTIR study confirms the formation of hydrogen bond. Phases exhibited by these mesogens are characterized by optical textural studies and Differential Scanning Calorimetry (DSC) studies. Phase diagram is constructed from these studies. Other thermal parameters such as order of the transition, thermal stability factor and specific heat are also elucidated. Optical tilt angle measurement and optical filtering action are also carried out. The influence of oxygen atom is also discussed.     

Crystal structures and hydrogen bond analysis of three arenesulfonate salts ofl-alanine,glycine, andl-serine

Single crystal X-ray structures are presented for three amino acid arenesulfonate salts:l-alanine 2,4-dinitrobenzenesulfonate hydrate (1), 21 glycine 1,5-naphthalene-disulfonate dihydrate (2), andl-serine 4-hydroxybenzenesulfonate (3). Hydrogen bond patterns of each salt are analyzed systematically by using hydrogen bond graph set notation. First-, second-, and selected third-level graph set motifs of the three salts are presented and discussed. Hydrogen-bonded diad, chain, ring, ribbon, and two-dimensional sheet patterns are identified in these structures. Even though the three salts contain apparently similar types of hydrogen-bonding interactions, their graph sets are quite different.Deceased June 10, 1992.     

Synthesis and mesomorphic behavior of symmetrical chiral liquid crystal dimers incorporating ester linked biphenyl- naphthyl cores and terminal vinyl group

A series of symmetrical chiral, liquid crystal dimeric molecules possessing ester- linked, biphenyl-naphthyl cores with varied spacer lengths and terminal vinyl groups have been synthesized using Naproxen as the synthetic precursor. The synthesized symmetrical chiral dimers were characterized by 1H NMR spectroscopy, and their liquid crystalline behavior was confirmed by DSC and HOPM studies. Structural effects on the mesomorphic and physicochemical properties were investigated in terms of variation of chiral chain length. The synthesized dimeric compounds exhibited SmX^*, SmC^*, SmA^*, N^*, BPI^*, and BPII^* mesophase sequences. An odd-even effect was observed in the dimers and the duration of the mesophase decreased with increasing spacer length. The synthesized vinyl substituted liquid crystalline dimers are particularly useful in understanding liquid crystal polymorphism and act as model compounds for liquid crystal polymers.     

Thermo‐morphological properties of the smectic C* mesophase in new chiral salicyaldimine liquid crystals

Specific textures and their temperature transformations in large temperature interval for the chiral smectic C* mesophase of new liquid crystalline materials, synthesized by our group, have been investigated in detail. Temperature dependences of the pitch of helical structure of the smectic C* mesophase have been determined for these materials. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low temperature powder diffraction and DFT solid state computational study of hydrogen bonding in NH4VO3

The crystal structure of NH₄VO₃ was refined by the geometry optimization done by total energy minimization in solid state using DFT/plane waves approach. The lattice parameters were derived by the Le Bail technique from the low temperature X‐ray (40‐293 K) and synchrotron (100‐293 K) powder diffraction data. The structure is formed by the infinite chains of irregular VO₄ tetrahedra running approximately parallel to the c‐axis, which are interlinked by the ammonium ions placed between them. The ammonium ions link to the [VO₄]_∞ chains through one linear, one bifurcated and two trifurcated N‐H…O hydrogen bonds. Considering their stability there are six distinct N‐H…O hydrogen bonds: two strong with the N‐H…O bond angles close to the straight, two medium with the bond angles of 123° and 148° and two very bent (105° and 107°) and hence weak hydrogen bonds. There is a reasonable agreement between the energies of the stretching ν(NH) modes estimated using the optimised N…O contact distances and those obtained experimentally. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Molecular and crystal structure of 4-hexylbenzoic acid: Design of the mesophase

The crystal structure of 4-hexylbenzoic acid C₆H₁₃-C₆H₄-COOH, which forms a nematic mesophase upon melting, is determined. The crystal contains three crystallographically independent molecules. Their molecular skeletons are made up of two almost planar fragments: a benzene ring, π-conjugated with the carboxyl group and a planar zigzag aliphatic fragment. One of the independent molecules forms centrosymmetric dimers via pairs of hydrogen bonds between carboxyl groups, whereas the two others are linked via hydrogen bonds. The dimers in the crystal are packed into pseudostacks with a pronounced nonparallel arrangement of conjugated fragments. There is no good mutual projecting of benzene rings in the stacks, which corresponds to efficient π-stacking interaction. The graph describing the mesophase of this compound contains only one structure-forming element (a hydrogen bond) and corresponds to the nematic mesophase.     

Mesomorphism dependence on molecular rigidity and flexibility

A novel homologous series of liquid crystalline properties is synthesized and studied with a view to understand the effect of molecular structure on its thermotropic properties. Novel homologous series consisted of thirteen homologs. All the homologs are enantiotropically smectogenic with absence of nematic property even in the monotropic condition. Textures of the homologs as observed through an optical hot stage polarizing microscopy. The mesophase temperature range vary minimum from 6.0°C to a maximum 37.0°C at the methyloxy and propyloxy derivatives of a series respectively with its thermal stability (Sm–I) 127.0°C. Transition curves of a phase diagram behaved in normal manner. Odd–even effect is observed for Sm–I transition curve.     

Conformation and segmental mobility of a diluted single polymer chain simulated with bond fluctuation model

The conformation of a single long polymer chain has been modelled using the Bond Fluctuation Model. The interaction between non-bonded segments has been introduced in the model by means of a Lennard-Jones potential while two energy potentials depending on bond length and bond angle took into account intramolecular interactions. The effect on chain configuration of varying bond angle potential, which tends to extend the polymer chain, was studied. The chain was allowed to equilibrate at high temperature, adopting a random coil conformation. When the system was subjected to a cooling ramp, its energy and dynamically accessible volume decreased but the system maintained the liquid conditions up to a temperature range in which the glass transition yielded a glassy coil with very restricted but not null segmental mobility. The remaining mobility in the glassy state, as well as its conformation, characterised through correlation functions, also depended significantly on the strength of bond angle potential. Further isothermal annealing yielded very compact structures, always amorphous with particular shapes depending on annealing temperature.     

Structure determination and hydrogen bonding of 1-naphthoxyacetic acid, a potential plant growth hormone

1-Napthoxyacetic acid crystallizes in the centrosymmetric space group C2/c (No. 15) with cell dimensions of a=14.273(2)Å, b=5.845(1)Å, c=24.211(1)Å, =105.815(2)°. The structure of the title compound reveals a carboxyl group-naphthalene ring dihedral angle of 4.85(14)°, O—H- - -O hydrogen bonded dimer, hydrogen bond distance of 2.640(2)Å, hydrogen bond angle of 172(2)°, and a cis configuration of O2 (double bond) and O3 relative to the C11—C12 bond all of which indicate that the title compound may be effective as a plant growth hormone.     

Preparation and Photoluminescent Properties of Hydrogen-bonded Discotic Liquid Crystals

Photoluminescent discotic liquid crystals (DLCs) have been prepared through intermolecular hydrogen bonding between core and peripheral units. 1,3,5-Trihydroxybenzene was employed as core molecule and peripheral stilbazole derivatives containing linearly conjugated moieties were complexed to form hydrogen-bonded DLCs. Their structures, mesophases, and optical properties were investigated. The complexation of core and peripherals made some discotic complexes form photoluminescent DLCs. The prepared luminescent DLCs exhibited columnar mesophases with strong blue or sea green photoluminescence. These findings may contribute to the development of luminescent supramolecular liquid crystals for emitting materials in light emitting devices.