Liquid crystalline 3-, 4- and 6-armed star molecules based on nitromethane-trispropanol or pentaerythritol without mesogen spacers

Some molecules of unusual shape and apparently non-linear geometry, with mesogens tied directly to a central unit (for example, tetrahedral pentaerythritol), have been investigated for liquid crystalline behaviour. It was found that these three-, four- and six-armed 'star' molecules generated liquid crystalline mesophases, which were characterized by DSC, optical microscopy and X-ray diffraction. The temperature ranges of the fluid mesophases for the thermotropic compounds were above 158°C for the three-armed molecules and above 219°C for the four-and six-armed 'stars'. All the liquid crystalline compounds exhibited a smectic phase, which appears to be smectic A, with the molecules in their fully extended conformations within the layers. Some of the compounds also had a smectic phase of higher order or a nematic phase.     

Phase characterization of LC (meth)acrylic monomers based on ω-hexyloxy- and ω-undecyloxy-salicylaldimine groups with different alkoxy tail substitutions

The synthesis and phase characterization of three homologous series of liquid crystalline acrylic and methacrylic monomers, consisting of 21 new compounds are presented. They are based on ω-hexyloxy- and ω-undecyloxysalicylaldimine groups with different alkoxy tail substitutions. The liquid crystalline materials were characterized by polarizing optical microscopy and differential thermal analysis. Smectic A and tilted smectic C phases were observed in the compounds. Near the transition to the isotropic, a narrow nematic phase, coexisting with the smectic A phase, was detected for the pentyloxy and hexyloxy derivatives in the M11 and A11 series. In case of M11R11 and M11R12 only a tilted smectic C phase was detected. The clearing point was comparable for all series, around 100°C.     

Phase characterization of LC (meth)acrylic monomers based on ω-hexyloxy- and ω-undecyloxy-salicylaldimine groups with different alkoxy tail substitutions

The synthesis and phase characterization of three homologous series of liquid crystalline acrylic and methacrylic monomers, consisting of 21 new compounds are presented. They are based on ω-hexyloxy- and ω-undecyloxysalicylaldimine groups with different alkoxy tail substitutions. The liquid crystalline materials were characterized by polarizing optical microscopy and differential thermal analysis. Smectic A and tilted smectic C phases were observed in the compounds. Near the transition to the isotropic, a narrow nematic phase, coexisting with the smectic A phase, was detected for the pentyloxy and hexyloxy derivatives in the M11 and A11 series. In case of M11R11 and M11R12 only a tilted smectic C phase was detected. The clearing point was comparable for all series, around 100°C.     

Interface induced crystal structures of dioctyl-terthiophene thin films

Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT sample from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films.     

New Schiff's bases containing 1,3,4-thiadiazole and 1,3,4-oxadiazole units: a study of the effect of the heterocyclic ring and the position of the lateral alkoxy group on liquid crystalline properties

The synthesis of novel Schiff's bases incorporating the five-membered 1,3,4-thiadiazole (series 7, 9) and 1,3,4-oxadiazole (series 8, 10) rings have been prepared and their liquid crystalline properties studied. All compounds of series 7 exhibit an enantiotropic smectic C phase. No liquid crystalline properties were observed for the compounds of series 8-10. A study of the structure/mesomorphic activity relationship is also described.     

New Schiff's bases containing 1,3,4-thiadiazole and 1,3,4-oxadiazole units: a study of the effect of the heterocyclic ring and the position of the lateral alkoxy group on liquid crystalline properties

The synthesis of novel Schiff's bases incorporating the five-membered 1,3,4-thiadiazole (series 7, 9) and 1,3,4-oxadiazole (series 8, 10) rings have been prepared and their liquid crystalline properties studied. All compounds of series 7 exhibit an enantiotropic smectic C phase. No liquid crystalline properties were observed for the compounds of series 8-10. A study of the structure/mesomorphic activity relationship is also described.     

Liquid crystalline properties of 4‐hexyloxybenzylidene‐4′‐alkyloxyanilines

The liquid‐crystalline polymorphism of the homologous series of 4‐hexyloxybenzylidene‐4′‐alkyloxyanilines is investigated. Basing on the polarization microscopy (POM, TOA), the DSC calorimetry and miscibility studies the following mesophases were detected: nematic, smectic A, smectic C and smectic I. The phase diagrams of the compounds of these series with 4‐hexyloxybenylidene‐4′‐pentylaniline (as the standard of mesophases) show induction of the smectic F mesophases. Their dependence on the alkyl chain length and mole fraction is shown.     

Conductive liquid crystalline compounds having a piperazine structure

New conductive thermotropic liquid crystalline materials having a piperazine ring in the central core: 1-[4-(9-decenyloxy)phenyl]-4-alkylpiperazines ( 6 ) were synthesized. The mesomorphic behaviours of these compounds and their conductivity in the liquid crystal phase were measured. The principal features of these compounds are to exhibit a smectic B phase around room temperature (for example 6 : Cr 50 SmB 81 I, °C) and to exhibit a large dark current (6d: 430 μA cm^-2, applied voltage 20 V, at 70°C) in the smectic B phase.     

X-ray study of the highly ordered smectic phases of N-pentyl-N'-(p-pentyloxyphenyl)piperazine

The structures of the highly ordered liquid crystalline smectic phases of N-pentyl-N'-(p-pentyloxyphenyl)piperazine are identified using X-ray diffraction methods. For this compound a phase sequence hexagonal smectic B (S_B)-orthofrhombic crystalline smectic H (C_H)-monoclinic crystalline smectic H (C_H) is observed for the first time. The changes in structural symmetry at the phase transitions are discussed.     

Anthraquinone derivatives as electron-acceptors with liquid crystalline properties

Dialkoxy derivatives of anthraquinone (AQ), dicyano-anthraquinone (DCAQ) and tetracyanoanthraquinone (TCAQ) were synthesized and their associated electrochemical, optical and self-assembling properties were investigated as candidates for n-type materials. AQ shows UV absorption features, whereas both DCAQ and TCAQ exhibit bathochromic and hyperchromic electronic transitions into the visible region. The electron accepting strength of the three compounds was established by cyclic voltammetry as -1.52 V, -1.3 V and -0.9 V vs. ferrocene/ferricenium for AQ, DCAQ and TCAQ, respectively. All three quinones displayed quasireversible, two sequential one-electron transfer redox reactions. DFT calculations of DCAQ and TCAQ demonstrate structural changes upon reduction, which is supported by spectroelectrochemical experiments. Furthermore, the structural changes result in different absorption profiles and show potential as electrochromic materials. Finally, both AQ and DCAQ show liquid crystalline phases and importantly, DCAQ exhibits both a smectic liquid crystalline and a soft crystal phase between -6 °C and 85 °C, which offers promise as a self-assembling n-type material.     

Conductive liquid crystalline compounds having a piperazine structure

New conductive thermotropic liquid crystalline materials having a piperazine ring in the central core: 1-[4-(9-decenyloxy)phenyl]-4-alkylpiperazines (6) were synthesized. The mesomorphic behaviours of these compounds and their conductivity in the liquid crystal phase were measured. The principal features of these compounds are to exhibit a smectic B phase around room temperature (for example 6: Cr 50 SmB 81 I, °C) and to exhibit a large dark current (6d: 430 μA cm^?2, applied voltage 20 V, at 70°C) in the smectic B phase.     

Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid

The liquid crystalline character of salts resulting from the interaction of poly(propylene imine) dendrimers with 3-cholesteryloxycarbonylpropanoic acid has been studied. The supramolecular structure and consequently the observed liquid crystalline phases are dictated by the degree of protonation of primary amino groups as compared with that of tertiary ones, determined by FTIR spectroscopy in the bulk and by NMR spectroscopy in solution. Glass transition temperatures of the materials are about 38°C. At higher temperatures they are transformed to smectic C* phases while a second-order smectic C phase to smectic A phase transition is observed between 90 and 110°C depending on dendrimer generation. At about 150°C the onset of degradation is observed. The influence of the ionic dendrimeric scaffold on the thermotropic properties is discussed.     

Structure and internal dynamics of a side chain liquid crystalline polymer in various phases by molecular dynamics simulations: a step towards coarse graining

Side chain liquid crystalline polymer with relatively long spacer was modeled on a semiatomistic level and studied in different liquid crystalline phases with the aid of molecular dynamics simulations. Well equilibrated isotropic, polydomain smectic and monodomain smectic phases were studied for their structural and dynamic properties. Particular emphasis was given to the analysis on a coarse-grained level, where backbones, side chains, and mesogens were considered in terms of their equivalent ellipsoids. The authors found that the liquid crystalline phase had a minor influence on the metrics of these objects but affected essentially their translational and orientational order. In the monodomain smectic phase, mesogens, backbones, and side chains are confined spatially. Their diffusion and shape dynamics are frozen along the mesogen director (the one-dimensional solidification) and the reorientation times increase by one to one-and-half orders of magnitude. In this phase, besides obvious orientational order of mesogens and side chains, a stable detectable order of the backbones was also observed. The backbone director is confined in the plane perpendicular to the mesogen director and constantly changes its orientation within this plane. The backbone diffusion in these planes is of the same range as in the polydomain smectic phase at the same temperature. A detailed analysis of the process of field-induced growth of the smectic phase was performed. The study revealed properties of liquid crystalline polymers that may enable their future fully coarse-grained modeling.     

Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid

The liquid crystalline character of salts resulting from the interaction of poly(propylene imine) dendrimers with 3-cholesteryloxycarbonylpropanoic acid has been studied. The supramolecular structure and consequently the observed liquid crystalline phases are dictated by the degree of protonation of primary amino groups as compared with that of tertiary ones, determined by FTIR spectroscopy in the bulk and by NMR spectroscopy in solution. Glass transition temperatures of the materials are about 38°C. At higher temperatures they are transformed to smectic C* phases while a second-order smectic C phase to smectic A phase transition is observed between 90 and 110°C depending on dendrimer generation. At about 150°C the onset of degradation is observed. The influence of the ionic dendrimeric scaffold on the thermotropic properties is discussed.     

Preorganised effects of a tetramesogenic supermolecule on supramolecular assembly in the liquid crystalline phases

After preparing a homologous series of tetrameric mesogenic compounds in which two U-shaped molecules were connected via a rigid benzene derivative or a flexible alkyl chain, we investigated their phase transition behaviour using optical microscopy, differential scanning calorimetry and X-ray diffraction analysis. The compounds possessing an alkyl spacer as the central group exhibited nematic and smectic A phases just as the corresponding U-shaped molecule did. The compound possessing a 1,2-benzene unit as the connecting group showed nematic and smectic A phases, although the compound possessing a 1,3-benzene unit exhibited only an anticlinic smectic C phase. Structure–property relations of the liquid crystalline tetramers are interpreted in terms of preorganised effects of the four mesogenic units.     

Thermotropic and lyotropic liquid crystalline behaviour of 4-alkoxyphenyl beta-D-glucopyranosides

The liquid crystalline properties of a series of 4-alkoxyphenyl beta -D-glucopyranosides (methoxy to decyloxy and dodecyloxy) were studied using polarized light microscopy and differential scanning calorimetry. The compounds with the shortest alkoxy substituents are not liquid crystalline. The butoxy derivative displays a monotropic smectic A phase and the higher homologues display enantiotropic smectic A phases. The lyotropic behaviour was studied as a function of concentration and temperature. Hexagonal, cubic and lamellar phases were observed for compounds with alkoxy chains longer than butoxy. The nonyloxy derivative forms long ribbons in dilute solution as revealed by electron microscopy.     

New possibility for an organic semiconductor: a smectic liquid crystalline semiconductor having a long conjugated core and two long alkyl chains

We report a new possibility for liquid crystalline organic semiconductors. These materials exhibit smectic liquid crystalline phases, in which the molecules assume a smectic molecular order by self-assembly. Because of the strong dispersion force among long alkyl chains, on cooling, smectic molecular order was retained at room temperature. A charge transport ability was also retained. The conductivity of a device having smectic liquid crystalline order is about 5×10⁷ that of a device with no smectic order. The current - voltage characteristic of the device has a very sharp increase at low threshold voltage (5 V). A high carrier mobility of 1.8×10^-2 was observed in the smectic phase of one of the compounds studied (e).     

Novel mesogenic asymmetric diacylhydrazines: synthesis, mesomorphic behaviour and X-ray study

The synthesis and liquid crystalline properties of a new series of diacylhydrazine derivatives (2a-g) are reported. All compounds of series 2 exhibit a smectic C (SmC) phase. The first homologues (2a, 2b) display a monotropic SmC mesophase, whereas the highest homologues (2c-g) exhibit an enantiotropic SmC phase. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray measurements.     

New possibility for an organic semiconductor: a smectic liquid crystalline semiconductor having a long conjugated core and two long alkyl chains

We report a new possibility for liquid crystalline organic semiconductors. These materials exhibit smectic liquid crystalline phases, in which the molecules assume a smectic molecular order by self‐assembly. Because of the strong dispersion force among long alkyl chains, on cooling, smectic molecular order was retained at room temperature. A charge transport ability was also retained. The conductivity of a device having smectic liquid crystalline order is about 5×10⁷ that of a device with no smectic order. The current?–?voltage characteristic of the device has a very sharp increase at low threshold voltage (5?V). A high carrier mobility of 1.8×10^‐2 was observed in the smectic phase of one of the compounds studied (e).     

Thermal properties and ionic conductivity of a polymer prepared by the in situ photopolymerization of a vinylimidazole monomer containing a mesogenic group

We have synthesized liquid crystalline polymers containing an imidazolium salt moiety and a mesogenic group by the in situ photopolymerization of a liquid crystalline vinylimidazole monomer in order to investigate the relationship between their thermal properties and ionic conductivity. A smectic phase was shown by the vinylimidazole monomer. The in situ photopolymerization of the monomer was carried out in the temperature range of the smectic phase. The polymer thus prepared displayed a highly ordered smectic phase in the temperature range between room temperature and about 200°C. The ionic conductivity of the polymer increased with increasing temperature. Anisotropic ionic conductivity behavior was observed for the polymer. The ionic conductivity of the polymer aligned homogeneously is larger than when homeotropically aligned.