Discotic Compounds Research Articles

Discotic liquid crystals of transition metal complexes 46: mesomorphism and antagonist solubility of octaphenoxy-phthalocyaninato copper(II) complex substituted by oligoether chains

We synthesized a novel discotic liquid crystalline compound, octakis[3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)phenoxy]phthalocyaninato copper(II) (abbreviated as [m- MeO(EtO)3PhO]8PcCu ), and established the mesomorphism by using a differential scanning calorimeter, a polarizing optical microscope, and temperature-dependent wide angle X-ray diffraction diffractometer. Very interestingly, this [m- MeO(EtO)3PhO]8PcCu complex showed a hexagonal ordered columnar (Colho) mesophase in the virgin sample, whereas it showed a rectangular ordered columnar (Colro(P21/a)) mesophase in the non-virgin sample. The Colho mesophase gave a dimer stacking distance at 9.26 Å, whereas the Colro mesophase gave a short monomer stacking distance at 3.45 Å. Furthermore, this novel Pc derivative is readily soluble in polar solvents such as acetone, ethanol and methanol. Using antagonist solubilities of the present hydrophilic [m- MeO(EtO)3PhO]8PcCu derivative in a polar solvent and the previous hydrophobic (C10O)16TzCu derivative in the non-polar solvent, a p-n junction layered thin films could be successfully prepared.

Synthesis and Mesomorphism of a Novel Triphenylene-Based Discotic Liquid Crystal with Chiral Chain

A novel triphenylene-based discotic liquid crystal compound was synthesized in this study. The chemical structures of compounds were characterized by 1HNMR spectra, FT-IR spectra and were confirmed. The phase transition behavior was studied in the combination of texture observation by DSC and POM equipped with a temperature-controllable hot-stage. The object compound showed liquid crystal phase and the results showed that columnar liquid crystal phase between 90.1°C and 138.1 °C during heating.

Synthesis and Mesophases Study on 2,3,6,7,10,11-Hexaheptylcarboxyltriphenylene

A triphenylene-based discotic compound 2,3,6,7,10,11-hexaheptylcar-boxyltriphenylene was synthesized. The structure of the compound was determined by1HNMR and FT-IR spectrum and its mesomorphism was clarified by DSC and POM methods. The carrier mobility was measured using time-of-flight method and has a value of 1.2 × 10-1cm2V-1s-1.

Photophysical and self-assembly properties of asymmetrical multi-aralkyl and arylaldehyde substituted pyrene derivatives

A series of novel asymmetrical pyrene derivatives with aralkyl and aldehyde groups have been successfully synthesized, and their spectroscopic parameters were investigated detailedly. The effects of aralkyl substituent amounts on the electronic absorption and emission spectra have been explored in evaluation of their potential as optical materials components. Moreover, the electrochemical properties of the new pyrene derivatives have been studied for the molecules' HOMO and LUMO levels by cyclic voltammograms. In particular, titration of anhydrous ethanol into dilute CH2Cl2 solution of above compounds, an unusual change of the fluorescence value was observed. The change is believed to correlate strongly to intermolecular charge transfer. The morphological evolution of self-assembled pyrene derivatives with (arylethynyl)aldehyde substituents, from tamen-distinct-like morphologies to vesicular textures, was obtained by increasing aralkyl-substituted fragments. These asymmetrical discotic compounds represent an interesting set of candidates for optoelectronic device components.

Progress in liquid crystal chemistry II

It is a great pleasure to introduce this second Thematic Series on Progress in liquid crystal within the Beilstein Journal of Organic Chemistry. Why liquid crystals? Liquid crystals have a major impact on our modern society, reaching from simple digital calculators to high-resolution flat-panel displays, and their market volume is expected to further increase. For example, in 2010 revenues of €1,013 million from sales of liquid crystals were reported by Merck, the world’s largest supplier of liquid crystal materials for electro-optical applications. This increase of 38% on 2009 was attributed to the demand for liquid crystal displays (LCDs). Forecasts predict annual global shipments of over 268.8 million LCD television sets by 2014 [1]. However, the chemistry behind liquid crystals, and particularly the synthesis, is the platform for such tremendous technological achievements, and this is true for both calamitic (rod-like) as well as discotic (disk-shaped) or other types of liquid crystals [2–4]. Since our initial Thematic Series Progress in liquid crystal two years ago [5], the research field has further broadened and stretches currently from materials science, through energy conversion and storage, to life sciences. The interested reader might be directed to a very recent special issue of Liquid Crystals edited by John W. Goodby to find more detailed information [6]. The review articles and original research papers of this second Thematic Series in the Beilstein Journal of Organic Chemistry, written by known experts of their field, cover diverse topics such as novel discotic and calamitic compounds, bent-core mesogens, amphiphiles, and liquid-crystalline nanoparticles. It is our goal to give the reader insight into both synthetic aspects of liquid crystal chemistry as well as application-oriented properties, such as photoconductivity or chirality transfer, to name just a few selected examples. Finally, we would particularly like to inspire people with complementary expertise, working in different fields of chemistry, to join forces with the liquid crystal community and to introduce their specific knowledge and objectives in order to aid the further advancement of this topic. Sabine Laschat Stuttgart, January 2012

A DIONE APPROACH TO MODIFY THE OPTICAL AND MESOPHASE PROPERTIES OF DISCOTIC TRIPHENYLENE DERIVATIVES

Two discotic liquid crystalline compounds, 6,7,10,11-tetra-pentyloxytriphenylene-1,4-dione and 6,7,10,11-tetra-heptyloxy- triphenylene-1,4-dione were synthesized and characterized. The synthesis consisted of two key steps: the preparation of 1,4-dimethoxy-6,7,10,11-tetra-alkoxytriphenylene and the oxidation to form the target compounds. In the latter step, the reaction was significantly improved using sodium nitrite in trifluoroacetic acid as an oxidant, resulting in an enhanced overall reaction yield and dramatically reduced reaction time. Both products show liquid crystalline phases, which were investigated using polarized optical microscopy and thermal analysis. The product with a longer side chain displayed a broader liquid crystal phase temperature range and favored a faster structure formation at low temperature. In addition to absorption at 272 nm, which is commonly observed in triphenylene-based discotic liquid crystals, the optical absorption of both compounds extends to the visible range, with extra absorption observed at 630 nm.

Synthesis and Mesophases Study on 2-(8-bromooctanoic acid ester)-3,6,7,10,11-penta-pentyloxytriphenylene

A novel triphenylene-based discotic liquid crystal compound 2-(8-bromooctanoic acid ester)-3,6,7,10,11-penta-pentyloxytriphenylene was synthesized in this study.The chemical structure of the compound was characterized by1HNMR spectra, FT-IR spectra and we confirmed its structure. The mesophases were investigated by using different scanning calorimetry DSC and polarizing optical microscopy POM, the results showed that the target product had Liquid crystal properties and the temperature range of 90-101 °C, and showed a clear columnar phase. The carrier transport mobility was measured using time-of-flight TOF method, μ=1.09*10-2cm2V-1s-1.

The Synthesis and Mesophases Studies of a Novel Discotic Compound Containing Two Triphenylene Cores Linked by Crown Ether

In this study, a novel discotic compound based on triphenylene core were synthesized. 6,7,10,11-tetrapentyloxy-2-hydroxy-3-methoxy triphenylene was synthesized via the common synthisis route including the Williamson Etherification of catechol, the iodination of 1,2-dipentyloxybenzene, the Ullman Coupling and the coupling of 3,3′-4,4′-tetrapentyloxy diphenyl and methoxy-phenol;Bis-(8-bromooctanoyl)-dibenzo-18-crown-6 was obtained from 8-bromooctanoic acid and dibenzo-18-crown-6 in polyphosphoric acid and then reacted in Et3SiH with trifluoroacetic acid as catalyst to obtain bis-(8-bromooctyl)-dibenzo-18-crown-6. Bis-(8-bromooctyl)-dibenzo-18-crown-6 reacted with 6,7,10,11-tetrapentyloxy-2-hydroxy-3-methoxy triphenylene via Williamson reaction to produce the goal product. The chemical structures of the compounds were identified by using fourier transform infrared spectroscopy, nuclear magnetic resonance and the thermal properties were characterized by optical polarizing microscope and differential scanning calorimeter.

Synthesis and Hole Transport Properties of Highly Soluble Pyrene-Based Discotic Liquid Crystals with Trialkylsilylethynyl Groups

Four pyrene-based discotic compounds with trialkylsilylethynyl groups in the side chains were prepared and characterized by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. All of the compounds were highly soluble in organic solvents, and two of the compounds exhibited a columnar phase, Colr, and the others were crystalline. The hole transport ability in the liquid-crystalline phases was determined by the time-of-flight (TOF) method to be on the order of 10−2 cm2 V−1 s−1, the highest hole mobilities for pyrene derivatives yet observed.

High‐Temperature Ferromagnetism of a Discotic Liquid Crystal Dilutely Intercalated with Iron(III) Phthalocyanine

Room-temperature ferromagnetism of an organic discotic liquid crystalline compound (DLC) is achieved by intercalation at low levels with paramagnetic iron(III) phthalocyanine (see figure). These ferromagnetic DLCs are very similar to the so-called dilute magnetic semiconductors of inorganic nature. It is expected that this novel approach will open up a new way of preparing the high-temperature organic ferromagnetic compounds needed for molecular spintronics.

Morphology of open films of discotic hexagonal columnar liquid crystals as probed by grazing incidence X-ray diffraction

The structure and the orientation of thermotropic hexagonal columnar liquid crystals are studied by grazing incidence X-ray diffraction (GIXD) for different discotic compounds in the geometry of open supported thin films. Whatever the film deposition mode (either spin-coating or vacuum evaporation) and the film thickness, a degenerate planar alignment with the liquid crystalline columns parallel to the substrate is found. However, if a specific thermal process is applied to the liquid crystal film, homeotropic anchoring (columns normal to the interface) can be stabilized in a metastable state.

Discotic liquid crystals of transition metal complexes 42: the detailed phase structures and phase transition mechanisms of two Cub mesophases shown by discotic liquid crystals based on phthalocyanine metal complexes

We found in our previous works that the sandwich-type phthalocyanine-based rare earth metal complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato]lanthanoid(III) ({[( C n O )2 PhO ]8 Pc }2 M, M = Eu and Lu , n = 8–16) (1 and 3), exhibited two thermotropic cubic mesophases, Cub1 and Cub2, together with columnar mesophases. It is rare that the discotic liquid crystalline compounds show the cubic mesophase. We revealed that their symmetries of the lower temperature Cub1 mesophase and the higher temperature Cub2 mesophase were [Formula: see text] and [Formula: see text], respectively. However, their detailed phase structures were not revealed in the previous works. In this work, we have synthesized a series of novel sandwich-type phthalocyanine-based terbium complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato]terbium(III) ({[( C n O )2 PhO ]8 Pc }2 Tb , n = 8–16) (2). Their mesomorphic properties have been investigated using polarization microscope, DSC and temperature-dependent X-ray diffraction techniques. As the result, the present Tb complexes (2) also showed two cubic mesophases, [Formula: see text] and [Formula: see text], together with columnar mesophases, as well as the previous Eu homologs (1) and Lu homologs (3). We have furthermore investigated by using temperature-dependent electronic absorption spectroscopy to reveal their detailed phase structures and phase transition mechanism of these two Cub mesophases. We have revealed that the [Formula: see text] mesophase forms a bicontinuous structure consisting of branched columns like jungle gym, but that the [Formula: see text] mesophase forms a discontinuous structure consisting of short columns like drums that resulted from the cutting off of the branched columns.

Synthesis and Optical/Thermal Behavior of New Azo Photoisomerizable Discotic Liquid Crystals

In this study, discotic azo compounds were prepared by a reductive coupling of 5-nitroisophthalic acid followed by a convergent synthesis, resulting in five new examples of azo photoisomerizable discotic molecules, which differ from each other by the linking groups (ester, amide or 1,3,4-oxadiazole) and number of aliphatic chain (4 or 8). The thermal and liquid crystalline properties of the compounds were completely characterized by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction analysis. Two products presented a stable columnar hexagonal mesophase with 95 and 134 °C of range. The results obtained show that the choice of the linking group and number of aliphatic chains has a significative influence in the materials properties. The photoisomerization capacity was evaluated in solution by spectroscopic methods and also by 1H NMR, indicating that these molecules are promising candidates for controlling the conductivity in electro-optical devices.

Synthesis and mesomorphic behaviour of new discotic liquid crystalline compounds containing triphenylamine as a core moiety via Sonogashira coupling

Design and synthesis of cholesterol based disk-like liquid crystalline compounds using triphenylamine as a core moiety have been achieved by Pd-catalyzed cross-coupling reaction. The newly synthesized compounds exhibit a cholesteric phase with fingerprint texture as well as oily texture. In the low temperature region, there is a signature of smectic B with characteristic dendritic and mosaic textures. The mesogenic properties were characterized by polarizing microscopy, differential scanning calorimetry and HRXRD studies.

Electrochemical Measurements and DFT Calculations of Discotic Liquid Crystalline Compounds

not Available.

Nanoscaled Discotic Liquid Crystal/Polymer Systems: Confinement Effects on Morphology and Thermodynamics

We have studied the influence of geometric confinement imposed on the supramolecular architecture of a discotic model compound confined to self-ordered nanoporous alumina. We systematically varied the pore diameter and the chemical nature of the pore walls and studied the systems thus obtained by means of wide angle X-ray diffraction and differential scanning calorimetry. A dominant planar core phase was found for high-energy pore walls consisting of alumina, whereas no apparent texture was present in the case of pore walls coated with non-polar poly(p-xylylene). Inside pores of 35 and 180 nm in diameter, pronounced geometric confinement effects and interfacial effects influence the structure formation. Additionally, we performed molecular dynamics simulations using a coarse-grained discotic potential.

Anisotropic light absorption, refractive indices, and orientational order parameter of unidirectionally aligned columnar liquid crystal films

The anisotropic optical properties of thermotropic columnar liquid crystals absorbing in the visible range are investigated for different discotic compounds unidirectionally oriented in open supported thin films. Two methods to monitor the alignment of columnar mesophases in thin films are reported, making possible to achieve either homeotropic anchoring (columns normal to the substrate) by a specific thermal annealing, or unidirectional planar orientation (columns parallel to the substrate) by using a rubbed Teflon coating. The columnar liquid crystal anchoring is found to depend on the nature of the compound, either parallel or perpendicular to the Teflon orientation. Based on this control of the mesophase alignment, the dichroic ratio and the orientational order parameter of oriented samples are measured, and a high order parameter of 0.9 is found in the case of parallel alignment. From the polarized absorption data of the columnar liquid crystal films, the light wavelength dependence of the birefringence and of the real and imaginary parts (refractive index and extinction coefficient, respectively) of the anisotropic optical indices are determined over the whole visible range.

Synthesis and Phase Structures of Novel π‐Acceptor Discotic Liquid Crystalline Compounds Having a Pyrenedione Core

AbstractSeveral π‐acceptor discotic liquid crystalline compounds were synthesized by using a pyrenedione unit as a core. Terrace‐like and band‐like structures were revealed by polarized optical microscopy (POM) observations and XRD measurements. In conjunction with the results of the single‐crystal structure analysis of analogous crystalline compounds, all of the liquid crystalline compounds were confirmed to form a discotic lamellar phase DL2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Characteristic dielectric parameters of columnar discotic hexa- n -alkoxyanthraquinones

Temperature-dependent dielectric spectroscopy of resynthesized discotic compounds, rufigallol hexa-n-alkoxylates for n = 6, 7, 8, 9 having wide temperature range (>70°C) hexagonal columnar mesophase has been carried out in the frequency range of 10 Hz to 10 MHz. The mesophase and their transition temperatures have been determined by using polarizing microscope and differential scanning calorimeter. Dielectric permittivity parallel () and perpendicular () to column have been determined. Using these data, dielectric anisotropy () has been found to be positive throughout the entire range of the Colh phase for all of the four compounds of this series. No relaxation phenomenon is found in the frequency range of 10 Hz to 10 MHz. The DC conductivity of these compounds has been found to be rather low (∼10−10–10−11 S-m−1). All the electrical parameters show odd–even effect with the variation of n.

Thermodynamic, optical and dielectric studies of the homologous members of columnar discotic compound Rufigallol hexa- n-alkoxylates

Thermodynamic, optical texture and frequency dependent dielectric studies of re-synthesized discotic compounds Rufigallol hexa- n-alkoxylates (for n = 6, 7, 8, 9) having wide temperature range hexagonal columnar (col h) mesophase have been carried out. The mesophase and their transition temperatures have been determined by using polarizing microscope and differential scanning calorimetry. Dielectric permittivity parallel ( ε ||′) and perpendicular ( ε ⊥′) to column axis have been determined. Using these two sets of data, dielectric anisotropy (Δ ε′ = ε ||′ − ε ⊥′) has been obtained which has been found to be positive throughout the entire range of the col h mesophase for all of the four compounds of this series. No relaxation phenomenon has been observed in the frequency range of measurement i.e. 10 Hz to 10 MHz. The DC conductivity of these compounds has been found to be rather low (~ 10 − 10 to 10 − 11 S m − 1 ). All the dielectric parameters show odd-even effect with the variation of n.