Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

• Marjan Krasna,
• Matej Cvetko and
• Milan Ambrožič

Beilstein J. Org. Chem. 2010, 6, No. 74, doi:10.3762/bjoc.6.74

• due to elastic forces. We study domain-type configurations of ensembles, which are quenched from the isotropic phase. We show that for large enough concentrations of NPs the long range uniaxial nematic ordering is replaced by short range order exhibiting strong biaxiality. This suggests that the

• nematic configuration represents the simplest liquid crystal phase [6]. In the bulk nematic phase LC molecules tend to be oriented homogeneously along a single symmetry breaking direction. At the mesoscopic level the average local orientational ordering is commonly described by the nematic director field

• . The directions ± of this unit vector field are physically equivalent, reflecting the so called head-to tail invariance of LC phase on the mesoscopic scale. If ensembles are suddenly quenched from the isotropic to the lower symmetry nematic phase, then unavoidably a domain pattern forms [7]. The reason

A surprising new route to 4-nitro-3-phenylisoxazole

• Henning Hopf,
• Aboul-fetouh E. Mourad and
• Peter G. Jones

Beilstein J. Org. Chem. 2010, 6, No. 68, doi:10.3762/bjoc.6.68

• , especially in flat-panel displays [2], light emitting diodes [3][4][5], anisotropic networks [6][7], and semiconductor materials [8]. Incorporation of the isoxazole moiety into such materials can result in significant changes in the corresponding mesogenic phases, since isoxazoles display classical nematic

Self-assembled ordered structures in thin films of HAT5 discotic liquid crystal

• Piero Morales,
• Jan Lagerwall,
• Paolo Vacca,
• Sabine Laschat and
• Giusy Scalia

Beilstein J. Org. Chem. 2010, 6, No. 51, doi:10.3762/bjoc.6.51

• found, possibly formed as a result of an intermediate lyotropic nematic state arising during the solvent evaporation process. Moreover, in sufficiently thin films the crystallization seems to be suppressed, extending the uniform order of the liquid crystal phase down to room temperature. This should be

• reminiscent of nematic organization. One explanation for the formation of planar alignment in thin films (generally thicker than those studied here, however) has been proposed by Grelet and Bock [15] in terms of the difference in surface tension at the different interfaces. In that case the stable LC order in

• the films appears only upon thermal annealing. While the same process might be occurring in our system, the evidence of nematic order – absent in the phase sequence of HAT5 – is difficult to explain following this scenario, suggesting that another or additional mechanism plays a role. One possible

Competition between local disordering and global ordering fields in nematic liquid crystals

• Matej Cvetko,
• Milan Ambrožič and
• Samo Kralj

Beilstein J. Org. Chem. 2010, 6, No. 2, doi:10.3762/bjoc.6.2

• Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 10.3762/bjoc.6.2 Abstract We study the influence of external electric or magnetic field B on orientational ordering of nematic liquid crystals or of other rod-like objects (e.g. nanotubes immersed in a liquid) in the presence of random

• structural transitions. Most studies so far have been carried out in thermotropic nematic LC phases, which exhibit long range orientational order [7]. To enforce disorder to LC ordering one either confines LC to various porous matrices [8][9][10][11][12] (e.g., aerogels, Controlled-pore glass, Vycor glass

• ]. Studies so far have mainly focused on structural and phase behavior [8][9][10][11][12][13][14][15][16][17][18]. It has been shown that the isotropic nematic phase transition is typically replaced by the paranematic–nematic (PN–N) phase transition. The transition temperature in most cases decreases with

Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues

• Aleksandra Jankowiak,
• Piotr Kaszynski,
• William R. Tilford,
• Kiminori Ohta,
• Adam Januszko,
• Takashi Nagamine and
• Yasuyuki Endo

Beilstein J. Org. Chem. 2009, 5, No. 83, doi:10.3762/bjoc.5.83

• stabilization of the nematic phase, upon CH2→O replacement, was observed in p-carborane mesogens relative to benzene analogues. Thus, in series 1–4, the nematic phase is stabilized by about 14 K more for the pairs 1A/2A and 3A/4A, than for terphenyl (D) and bicyclo[2.2.2]octane (C) analogues (Figure 2

• to analyze the effect of the replacement of an alkoxy in 14[6] with an ester group in 15[6]. The CH2O→OOC exchange dramatically destabilized the nematic phase for the 10- and 12-vertex p-carborane derivatives, while a much smaller effect was observed for the carbocycles [25]. Series 14 and 15 [25

• exclusively the nematic phase. Similar nematic behavior is observed for carbocycles in series 17–20 with the exception of 19D, which exhibits a SmA phase in addition to a N phase. In contrast, most carbocyclic derivatives in series 14[6]–16[6] display only smectic and soft crystalline polymorphs. The bicyclo

Low temperature enantiotropic nematic phases from V-shaped, shape-persistent molecules

• Matthias Lehmann and
• Jens Seltmann

Beilstein J. Org. Chem. 2009, 5, No. 73, doi:10.3762/bjoc.5.73

• temperature range nematic. For the optimised mesogen structure, optical investigations by conoscopy monitored a uniaxial nematic phase upon cooling from the isotropic phase to room temperature (ΔT = 150 °C). X-ray studies on magnetic-field-aligned samples of this mesogen family revealed a general pattern

• engineering; thiadiazoles; V-shaped mesogens; Introduction Most molecules forming nematic liquid crystals, the nematogens, are based on rod-shaped (calamitic), anisometric cores with peripheral flexible chains along the molecular long axis [1]. Nematic phases are the simplest liquid crystalline mesophases

• , in which phase anisotropy of crystals is combined with fluid properties of liquids. In the nematic phases of calamitic mesogens only the molecular long axes are oriented along a so called director [2] and the molecular centres of gravity are distributed like in a liquid. In models, the molecules are

Molecular length distribution and the formation of smectic phases

• Nadia Kapernaum,
• C. Scott Hartley,
• Jeffrey C. Roberts,
• Robert P. Lemieux and
• Frank Giesselmann

Beilstein J. Org. Chem. 2009, 5, No. 65, doi:10.3762/bjoc.5.65

• mixtures of chemically similar smectogenic mesogens strongly differing in molecular length were investigated. In these mixtures the nematic phase present in the pure short mesogen disappeared rapidly on the addition of the longer mesogen, while the smectic state was preserved. In the smectic state the

• optimised mixtures consisting of several mesogenic compounds and non-mesogenic additives such as chiral dopants or UV-stabilizers. While the design of nematic mixtures is highly developed and widely applied, far less is known about the mixing of smectics and the particular effects thereof. In principle the

• bimodal) changes the structure and properties of the nematic and the SmA phases and the (possible) tilting transition to smectic C (SmC). As a general first approximation calamitic mesogens are considered as rigid rods. This means they are treated as long and thin hard spherocylinders [2]. The

Coaxial electrospinning of liquid crystal-containing poly(vinylpyrrolidone) microfibres

• Eva Enz,
• Ute Baumeister and
• Jan Lagerwall

Beilstein J. Org. Chem. 2009, 5, No. 58, doi:10.3762/bjoc.5.58

• composite fibre with core–sheath structure [10][11][12]. Recently it could be shown that also a room temperature nematic liquid crystal (LC) can be coaxially spun with a composite sheath of TiO2 and poly(vinylpyrrolidone) (PVP) [13]. Such composite fibres with a core exhibiting the responsiveness and

• PVP as sheath and the liquid crystal 4-cyano-4′-octylbiphenyl (8CB) as core produced by coaxial electrospinning. The latter LC exhibits a smectic phase (phase sequence: cryst. 20.5 SmA 32.0 N 39.2 iso.) in contrast to the LC used in our previous work, which formed only a nematic liquid crystal phase

• nematic transition, on the other hand, is shifted to higher temperatures with decreasing LC content of the fibres until it finally disappears in the last shown sample (in = 5 µl h−1). During this process the shape of this transition in the thermogram transforms continuously from a peak in the bulk to a

Functional properties of metallomesogens modulated by molecular and supramolecular exotic arrangements

• Alessandra Crispini,
• Mauro Ghedini and
• Daniela Pucci

Beilstein J. Org. Chem. 2009, 5, No. 54, doi:10.3762/bjoc.5.54

• the ancillary ligand. Indeed a transition from a calamitic to a columnar mesophase is observed, through a calamitic/discotic cross-over point, due to the peculiar combination of two different molecular architectures. The mononuclear tropolonate derivative (A in Figure 2) shows a chiral nematic phase

Novel banana-discotic hybrid architectures

• Hari Krishna Bisoyi,
• H. T. Srinivasa and
• Sandeep Kumar

Beilstein J. Org. Chem. 2009, 5, No. 52, doi:10.3762/bjoc.5.52

• switched in external electric fields. Various new applications of these materials include nonlinear optics, flexoelectricity, photoconductivity, molecular electronics and the design of biaxial nematic phases [8][9]. In addition to various banana phases, these mesogens also display classical nematic

A convenient method for preparing rigid-core ionic liquid crystals

• Julien Fouchet,
• Laurent Douce,
• Benoît Heinrich,
• Richard Welter and
• Alain Louati

Beilstein J. Org. Chem. 2009, 5, No. 51, doi:10.3762/bjoc.5.51

• governs the formation of a multitude of supramolecular architectures depending on the temperature (thermotropic liquid crystals) and/or of the solvent (lyotropic liquid crystals) [7][8]. In the case of the thermotropic liquid crystals the arrangements give rise to nematic phases (molecules are aligned

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• Abstract The addition of a chiral non-racemic dopant to a nematic liquid crystal (LC) has the effect of transferring the molecular chirality to the phase organization and a chiral nematic phase is formed. This molecular chirality amplification in the LC provides a unique possibility for investigating the

• efficient chiral inducers in biaryl nematic mesophases. In this paper, we focus on a new series of helicene-like molecules of known absolute configuration. We have integrated cholesteric pitch measurements with geometry optimization by DFT calculations and analysis of the twisting ability by the Surface

• ; helicene; nematic liquid crystal; Surface Chirality model; Introduction Nematic liquid crystals (LCs) are fluid phases formed by anisometric molecules which, though free to rotate as in ordinary liquids, are preferentially aligned along a common axis, called director. The addition of a chiral non-racemic

Progress in liquid crystal chemistry

• Sabine Laschat

Beilstein J. Org. Chem. 2009, 5, No. 48, doi:10.3762/bjoc.5.48

• smectic phases, nematic phase engineering by using V-shaped molecules, saddle-shaped columnar systems displaying anomalous odd-even effects, theoretical studies on the origin of chirality transfer in liquid crystalline host-guest systems, liquid crystalline carboranes and dyes and discotic phenanthrene

Shape- persistent macrocycle with intraannular alkyl groups: some structural limits of discotic liquid crystals with an inverted structure

• Sigurd Höger,
• Jill Weber,
• Andreas Leppert and
• Volker Enkelmann

Beilstein J. Org. Chem. 2008, 4, No. 1, doi:10.1186/1860-5397-4-1

• peripheral flexible side groups that point outward [13][14][15][16]. They can be used for a variety of different optic and electronic applications, for example as materials for photovoltaics (in the columnar phase) [17][18][19] or as compensation layers in display technology (in the nematic phase) [20][21

• of the compound. The term adaptable means that the orientation of substituents at that position can be influenced by an external parameter [25][26]. Compound 1 melts at 134 °C to form a nematic mesophase that becomes isotropic at 159 °C. However, compared to all previously reported discotic LCs, this

• mesophases. However, reports about shape-persistent macrocycles with extraannular PAH substituents are absent. If these compounds exhibit liquid crystallinity, the question about the mesogenic element (ring or PAH or both) arises. Additionally, biaxial nematic phases might be observable [31][32]. The