Discotic Columnar Phase Research Articles

Rods to discs in the study of mesomorphism in discotic liquid crystals

ABSTRACTThe rational design of calamitic liquid crystals is an area of research that has been intensively explored due to their extensive applications in various devices. The successful methods for design have been, to some extent, mapped on discotic systems such that certain features of the structures of calamitic phases have been superimposed upon those of nematic discotic and columnar phases. In this article, we explore the correlation between nematogenic behaviour of hard rod-like particles and that of hard disc-like systems. We show that for calamitics, nematic behaviour is observed, whereas for discotics this is not the case. Furthermore, we show that nematic discotic materials are miscible, whereas unlike smectics, columnar phases are less likely to be miscible. Indeed, it appears that columnar discotic phases are greater similarities with soft-solids than true liquid crystals.

Synthesis and liquid crystalline studies of disc-shaped molecule on azo-bridged benzothiazole-phenyl ethers

A new series of triphenylene core attached by six peripheral arms containing benzothiazole-azo with terminal ethoxy unit have successfully been synthesized and their liquid crystalline properties were characterized. The members in this series differ by the length of the methylene unit of (CH2)n, where n, varied following ascending order from 5 to 10. The molecular structure was characterized by elemental (C, H and N) analysis and spectroscopic methods including Fourier Transform Infrared (FT-IR) and Proton Nuclear Magnetic Resonance (1H NMR). The texture and the phase transition temperatures were investigated by using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The disc-shape molecule with shorter spacer (n=5) showed monotropic nematic phase. The higher homologues with n=8–10 exhibited enantiotropic nematic phase and monotropic smectic C phase. The XRD diffraction studies further confirm the presence of smectic C without any discotic columnar phase.

Mesophase Transformation of Mixed Liquid Crystals Formed by Supramolecular Self‐Organization of 4‐Substituted Benzoic Acids

AbstractA mixed liquid crystalline system consisting of 4‐(octadeca‐1,3‐diynyl)benzoic acid (14PhDA) and 4‐tetradecanoxybenzoic acid (14OBA) exhibits different mesophases depending on their composition and the temperature. A mechanism is investigated for the formation of mixed liquid crystalline phases and the transformation of smectic to discotic lamellar mesophases. The three kinds of mesophases, the discotic columnar phase of 14PhDA, the smectic C phase of 14OBA, and the discotic lamellar phase of a mixture of 14PhDA and 14OBA, are simultaneously observed in a temperature range from 110 to 140 oC during the process of formation of the mixed liquid crystals by the molecular diffusion of 14PhDA and 14OBA. After rapid cooling the sample to room temperature, microscopic IR spectra are measured to estimate the composition ratio of 14PhDA and 14OBA at local positions in each mesophase. The composition ratio discontinuously changes at the boundary between the 14OBA and 14PhDA/14OBA phases due to a significant difference in the mesophase structures, i. e., the calamitic and the discotic phases, while the 14PhDA content continuously increases at another boundary between the 14PhDA/14OBA and 14PhDA mesophases. It is concluded that the diffusion of 14OBA dimer from the smectic phase to the discotic lamella phase is fast in contrast to the slow diffusion of disc‐like mesogens included in the discotic mesophases.

Historical Overview of Polar Liquid Crystals

Brief history of ferroelectric and antiferroelectric liquid crystals is described. To reduce the symmetry of the molecular systems, two ideas were successfully used; introductions of chirality and molecular shape asymmetry. The chirality introduced into rod-shaped and disc-shaped molecular systems led to chiral smectic C and chiral discotic columnar phases. Dogleg from rod and cone or bowl from disc in molecular shapes brought about polar organization by their packing, realizing so-called banana phases and polar columnar phases, respectively. Particularly, bent-core mesogens exhibit a variety of novel polar phases. In addition to such established polar structures, some evidences about polar structures realized in polar nematic and cholesteric phases are given in some detail. Attempts for the application of these polar liquid crystals such as displays are also overviewed.

Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-bonded complexes

We report the synthesis and investigation of a new self-assembled benzoylhydrazine-based compound, namely 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine and their hydrogen-bonded complexes with different carboxylic acid derivatives, of which some exhibit liquid crystalline properties and some are non-mesogens. The conversion of the non-liquid crystalline target compound that is free from carboxylic acid to liquid crystalline complexes containing various carboxylic acids can probably be rationalised through the breaking of intermolecular hydrogen bonding within the supramolecular assembly by carboxylic acid dopants. The enhancement of liquid crystalline properties of benzoylhydrazine compounds with respect to various carboxylic dopants is documented. Other salient features can be exemplified by the formation of discotic columnar phase as shown by the azo-linkage containing 4-(4′-(10-decyloxy)phenylazo)benzoic acid-doped complex.

Absolute determination of the orientational order quality in a columnar discotic liquid crystal

ABSTRACTSimple NMR techniques can provide an absolute quantification of the quality of the orientational order of discotic columnar phases, provided the anisotropic local magnetic interactions are thoroughly characterized. For the prototypical discotic liquid crystal hexapentoxy-triphenylene, we measure the 13C chemical shift anisotropy of the triphenylene carbons, and use this result to analyze the orientational order, that occurs through a first order phase transition from the high temperature liquid phase, and is almost saturated (order parameter close to 0.85).

Fluorescent lanthanide complexes of Schiff base ligands possessing N-aryl moiety: influence of chain length on crossover (calamitic to discotic) phase behaviour

New lanthanide complexes, Tb(III), Dy(III) and Gd(III) of N-aryl based Schiff bases exhibiting mesomorphism have been synthesised and characterised. The crossover phenomena of calamitic lamellar to discotic columnar phase behaviour in these lanthanidomesogens is found to be controlled by the variation in chain length of the single alkyl substituent on the terminal N-aryl ring, hitherto the first case of a metallomesogen with only one alkyl chain length at each end of the ligand as evidenced by thermal microscopy studies and complemented by X-ray studies. It is also observed as a function of temperature in a single component. The electronic properties of these systems are dominated by the donor–acceptor substituted organic chromophore ligand, and the emission maxima revealed a large Stokes shift of 160 nm. The ligand–ligand charge transfer is reflected in emission spectra and is due to the presence of phenyl rings in the ligands.

Lamellar Nanoconfinements Effects in Discotic Liquid Crystalline Block Copolymers

AbstractWe have evaluated the effect of slit‐like nanoconfinements imposed on columnar discotic phases within a discotic block copolymer displaying a lamellar microphase. Findings are that the columns are oriented uniformly along the lamellar normal within the plane of thin films, that a rectangular rather than a hexagonal columnar phase is formed within the discotic regions, that the thermodynamic stability of the columnar phase is strongly reduced relative to the low molar mass model compounds and finally, that the isotropic phase can be unusually strongly supercooled with respect to the columnar phase formation. Slit‐like nanoconfinements allow thus to induce novel types of the intrinsic order and columnar orientations.magnified image

Synthesis of Tripod-shaped Liquid Crystals with sp3Nitrogen at the Apex

nigrogen at the apex were prepared from triethanolamine. Their physical properties were investigated by using optical microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The XRD study suggests that the tripod-shaped molecules show the 2D-ordered phase of either the frustrated smectic layer structure or discotic columnar phases.

Separation of dialkyl sulfides by metallomesogenic stationary phases for complexation gas chromatography

A copper mesogenic side-chain polymer (P-C 15CuC 18) was cross-linked onto the capillary wall as a stationary film for gas chromatography (GC) separation of alkylsulfides. These organic sulfides are of interest for their large health impact because of their wide range of volatilities and high reactivities toward metals. Different GC parameters for optimal separation efficiency are discussed for use with a mesogenic polymer column along with flame photometric detection (FPD). Both the carrier gas flow-rate and column temperature were studied to determine the relationship of plate height to the chemical structure of the solutes, as well as to determine the morphology of the mesogenic polymer. Van ’t Hoff plots show phase transitions of the stationary mesophase as the column temperature was varied. The results reveal that the separation mechanism might be based on ligand exchange and polarity interaction between the analytes and the stationary phase, with the vapor pressure of the analytes also being important. The former interaction dominates in the lamellar crystalline phase and the latter interaction dominates in the hexagonal columnar-discotic phase. With high reproducibility for retention time (RSD ≤ 0.37%) and for peak area (RSD ≤ 5.16%), the GC–FPD system produced linear calibration graphs ( r ≥ 0.9918) for the determination of 13 sulfides with a detection limit below 2.5 ng.

Atomistic simulation of structure and dynamics of columnar phases of hexabenzocoronene derivatives

Using atomistic molecular dynamics simulations we study solid and liquid crystalline columnar discotic phases formed by alkyl-substituted hexabenzocoronene mesogens. Correlations between the molecular structure, packing, and dynamical properties of these materials are established.

Fast Electron Transport in Discotic Columnar Phases of Triphenylene Derivatives

We investigated the negative carrier transport in discotic columnar phases of three triphenylene derivatives by time-of-flight experiments. We found that transient photocurrents had two transits of negative carriers, which appeared in different time ranges. The mobilities obtained from the fast transit were 2×10-2, 2×10-3, and 4×10-4 cm2/(V·s) for 2,3,6,7,10,11-hexabutyloxytriphenylene (H4T), 2,3,6,7,10,11-hexapentyloxytriphenylene (H5T) and, 2,3,6,7,10,11-hexahexyloxytriphenylene (H6T), respectively. These mobilities are almost the same as hole mobilities for each triphenylene derivative, indicating electron transport. On the other hand, the mobilities from the slow transit were about 10-5 cm2/(V·s), and exhibited the Arrhenius type of temperature dependence irrespective of the three triphenylene derivatives, indicating ionic transport. We discuss the nature of the negative carrier transport in triphenylene derivatives including the electronic and ionic transports.

Electronic and ionic carrier transport in discotic liquid crystalline photoconductor

We have investigated the negative charge carrier transport in discotic columnar phases of triphenylene derivatives, 2,3,6,7,10,11-hexapentyloxytriphenylene (H5T) and its related derivatives such as H4T and H6T, by time-of-flight experiments. We observed a fast transit for negative charge carriers in the discotic hexagonal columnar phase $({D}_{h})$ of H5T, which corresponded to a high mobility of ${10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ comparable to its hole mobility, in addition to a slow transit corresponding to the mobility of ${10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.3em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ reported previously. We observed two transits in H4T and H6T as well, in which the fast mobility was on the order of ${10}^{\ensuremath{-}2}$ and ${10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ in H4T and H6T, respectively, while the slow mobility was almost the same $(3\ensuremath{-}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$ in both H4T and H6T. Through dilution experiments with $n$-dodecane, we found that these fast and slow transits were attributable to the electronic and ionic conduction, respectively, and that the latter was caused by negatively ionized impurity molecules trapping photogenerated electrons. We discuss that there exist two distinct carrier transport channels for electronic and ionic charges in the intrinsic nature of discotic columnar phases.

Fast Electron Transport in Discotic Columnar Phase of Triphenylene Derivative, Hexabutyloxytriphenylene

We have re-investigated the charge carrier transport in a discotic columnar phase of triphenylene derivative, hexabutyloxytriphenylene (H4T) by time-of-flight experiments. We observed two transits for negative charge carriers in a different time range that corresponded to a fast mobility of 10−2 cm2/Vs and a slow mobility of 10−5 cm2/Vs in the discotic hexagonal plastic phase of H4T, while a high mobility on the order of 10−2 cm2/Vs as reported previously. These were attributed to the electronic conduction caused by fast electron transport along with the discotic columns and slow ionic conduction caused by drift of ionized impurity molecules that accepted photo-generated electrons, respectively.

Short chain copper(II) n-alkanoate liquid crystals

Four short chain members of the copper(II) n-alkanoate series Cu(Cn)2, from propanoate to hexanoate, have been synthesized, purified and characterized by means of optical microscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), FTIR and Raman spectroscopy. The TGA study shows that decomposition starts on heating above 420–470 K (depending on the sample) in a nitrogen atmosphere. In addition, thermal decomposition was investigated by DSC using special high pressure pans and endo- and exc-thermic processes were found which have not been reported previously. All but one of the compounds melt to a liquid crystal phase, which decomposes before the clearing point. The exception is the propanoate homologue, which decomposes directly from the solid state. Despite this problem of sample decomposition, the identification by optical microscopy of the tetragonal (butanoate) and hexagonal (pentanoate and hexanoate) discotic columnar phases was, for first time, possible by the addition of small amounts of the corresponding acid to the samples. These results are in agreement with the X-ray diffraction study performed using swelled mixtures of these salts with hydrocarbon solvents. Two solid–solid transitions, not previously reported in the literature, were found for the butanoate homologue at 395.9 and 422.9 K with ΔH=8.27 and 1.37 kJ mol−1, respectively. The solid and liquid crystalline phases were investigated using variable temperature FTIR spectroscopy.

3A04 Triphenylene誘導体Discotic相における高速の電子輸送特性(物理・物性)

3A04 Triphenylene誘導体Discotic相における高速の電子輸送特性(物理・物性)

Photoconductivity Measurements in the Discotic Columnar Phase of a few Anthraquinone Derivatives

It has recently been shown that the structure of the columnar phase of discotic liquid crystals is suitable for fast transport of photogenerated charge carriers. Although the magnitude of the charge carrier mobility exhibited by these systems is still small compared to those in organic single crystals, the fluidity and the resulting self-healing nature of the liquid crystalline columnar phases hold promises for potential applications. In this paper we report on steady-state photoconductivity measurements carried out on three anthraquinone derivatives exhibiting the columnar phase. Upon illumination of the sample with UV light the current through the sample increases abruptly and reaches a photo-stationary value within a short span; the fastest observed response time is 17 ms. It was found that the anisotropy of the photoconductivity, defined as the ratio of the photocurrent along and perpendicular to the column axis, reaches a value of about 450. We also discuss the relation between the chemical structure of the molecule and the maximum value of the photocurrent observed.

Synthesis and thermal properties of liquid crystalline side chain polymers with pendant cellobiose residues

Two series of thermotropic polymethacrylate (PM) samples with pendant cellobiose residues and an alkyl spacer (number of carbon atoms n = 4 and 10) were synthesized, and their mesomorphic properties were investigated to elucidate the function of acylated cellobiose moieties as discotic mesogens by differential scanning calorimetry (DSC), polarization microscopy and X-ray diffraction. The PM-4 samples with a short spacer (n = 4) showed two kinds of mesophases in a wide temperature region up to the degradation temperature of the sample, i. e., about 230°C, whereas the PM-10 samples with a long spacer (n = 10) showed a single mesophase between 45 and 135°C. X-Ray diffraction data suggested that both the mesophases formed by PM-4 and PM-10 belong to a kind of discotic columnar phases in which the side chain mesogens form the discotic columns around the polymer backbone.

Synthesis and thermal properties of liquid crystalline side chain polymers with pendant cellobiose residues

Two series of thermotropic polymethacrylate (PM) samples with pendant cellobiose residues and an alkyl spacer (number of carbon atoms n = 4 and 10) were synthesized, and their mesomorphic properties were investigated to elucidate the function of acylated cellobiose moieties as discotic mesogens by differential scanning calorimetry (DSC), polarization microscopy and X-ray diffraction. The PM-4 samples with a short spacer (n = 4) showed two kinds of mesophases in a wide temperature region up to the degradation temperature of the sample, i.e., about 230 °C, whereas the PM-10 samples with a long spacer (n = 10) showed a single mesophase between 45 and 135°C. X-Ray diffraction data suggested that both the mesophases formed by PM-4 and PM-10 belong to a kind of discotic columnar phases in which the side chain mesogens form the discotic columns around the polymer backbone.

A Plastic Columnar Discotic Phase

A plastic columnar discotic phase is reported for several triphenylene derivatives. It is characterized by a three-dimensional positional order of the molecules, as in a crystalline state, while maintaining the rotational mobility of the molecules. Only very minute changes in structure and dynamics occur at the phase transition from the normal discotic hexagonal phase to the discotic plastic phase.