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Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid-crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacrylate mesogen consisting of an azobenzene core and discrete oligodimethylsiloxane tails. The synchronous helical photoalignment and photopolymerization originate from the cooperative movement of the mesogens ordered in well-defined responsive structures, together with the flexibility of the oligodimethylsiloxane blocks. The resulting thin films show excellent thermal stability and light-induced memory features with reversible responses. Additionally, we demonstrate the fabrication of photo-patterned films of liquid-crystal networks with opposite helical senses. These findings provide a new method to make light-controllable chiroptical materials with exciting applications in optics and photonics.

The synthesis and thermotropic behaviour of some di-alkyloxy-phenyl-1,2,4-triazolium trifluoromethane-sulfonate salts bearing a seven-carbon atom perfluoroalkyl chain on the cation is herein described. The fluorinated salts presenting a 1,2,4-triazole as a core and differing in the length of two alkyloxy chains on the phenyl ring demonstrated a typical liquid crystalline behaviour. The mesomorphic properties of this set of salts were studied by differential scanning calorimetry and polarized optical microscopy. The thermotropic properties are discussed on the grounds of the tuneable structures of the salts. The results showed the existence of a monotropic, columnar, liquid crystalline phase for the salts tested. An increase in the temperature mesophase range and the presence of two enantiotropic mesophases for the sixteen-atom alkyloxy chain salt can be observed by increasing the length of the alkyloxy chain on the phenyl ring.

The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts.

We investigate the isotropic, uniaxial nematic and biaxial nematic phases, and the transitions between them, for a model lyotropic mixture of flexible molecules consisting of two rigid rods connected by a spacer with variable bending stiffness. We apply density-functional theory within the Onsager approximation to describe strictly excluded-volume interactions in this athermal model and to self-consistently find the orientational order parameters dictated by its complex symmetry, as functions of the density. Earlier work on lyotropic ordering of rigid bent-rod molecules is reproduced and extended to show explicitly the continuous phase transition at the Landau point, at a critical bend angle of 36.. For flexible dimers with no intrinsic biaxiality, we find that a biaxial nematic phase can nevertheless form at a sufficiently high density and low bending stiffness. For bending stiffness kappa > 0.86k(B)T, this biaxial phase manifests as dimer bending fluctuations occurring preferentially in one plane. When the dimers are more flexible, kappa < 0.86k(B)T, the modal shape of the fluctuating dimer is a V with an acute opening angle, and one of the biaxial order parameters changes sign, indicating a rotation of the directors. These two regions are separated by a narrow strip of uniaxial nematic in the phase diagram, which we generate in terms of the spacer stiffness and particle density. info:eu-repo/semantics/publishedVersion

7 pages; International audience; A series of five-membered heterocyclic 1,2,3-triazole derivatives with different substituents in N1 position was synthesized. The heterocyclic moiety was connected through an ester function to a p-decyloxyphenyl or p-decyloxybiphenyl tails Polarized microscopy studies, X-ray scattering and differential scanning calorimetry (DSC) analysis revealed that the target compounds exhibit enantiotropic liquid crystalline properties. Their mesomorphic behavior is closely related to the nature of the substituent X present in N1 position of the heterocycle.

The effect of dipole substitution on the self-assembly, thermodynamics, and dynamics has been studied in a series of hexa-peri-hexabenzocoronenes (HBCs). The HBCs bear the same number and type of aliphatic chains, but different dipoles directly attached to the cores ranging from similar to 0 to similar to 3.4 D. Dipole substitution alters the energetics and reduces the transition temperature favoring the columnar hexagonal liquid crystalline phase at the expense of the crystalline phase. The equation of state was obtained by independent pressure volume temperature measurements in both phases that resulted in the equilibrium phase diagram. According to the latter, increasing pressure imparts stability to the crystalline phase. The molecular and supramolecular dynamics investigated, respectively, by dielectric spectroscopy and rheology, identified a hierarchy of motions comprising a fast axial motion, a slower process that completely relaxes the dipole moment, and an even slower soliton-like relaxation of structural defects. Journal of Physical Chemistry B

The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Colh) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C10Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C10Br, a 'high temperature' glass transition, manifested by a Vogel-Fulcher-Tammann (VFT) type α2-process, was found at -31 °C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (α1) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as -100 °C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a 'hindered' polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails. © 2005 Elsevier B.V. All rights reserved. ispartof: JOURNAL OF NON-CRYSTALLINE SOLIDS vol:351 issue:33-36 pages:2622-2628 ispartof: location:NETHERLANDS, Delft status: published

Two series of asymmetric banana-shaped compounds have been synthesized and studied. In the 1,3-phenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the lack of symmetry was derived solely from the difference in length of the two terminal alkoxy chains. In the 3,4'-biphenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the asymmetric nature originates from the 3,4'-substitution of the central biphenyl group and from the difference in length of the two terminal chains. All the melting points of the asymmetrical compounds in the series with the central phenyl unit are lower than those of the symmetrical compounds. The liquid crystalline B-1 or B-2 phase was retained in all cases. In the series with the central biphenyl unit the compounds with the shortest chain attached to the para -position of the central biphenyl unit have the lowest melting points. A significant lowering of the melting points in comparison with the symmetrically substituted compounds, however, could not be achieved. All the compounds of both series show a layer spacing which is comparable to those of the symmetrically substituted parent compounds. The observed switching behaviour of both the symmetric and asymmetric compounds with a B-2 phase was antiferroelectric.

Stereospecific formation of aryl 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside was achieved by reaction of penta-O-aceeyl-beta-D-glucose 1 with substituted phenols in the presence of boron trifluoride. Yields of the purified products varied from 52-85%. Benzyl alcohol could also be glucosylated using similar conditions. All products were purified by crystallization from ethanol. The purity and the anomeric configuration of the products were determined by means of H-1 and C-13 NMR spectroscopy melting points and optical rotation.

Stereospecific formation of aryl 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside was achieved by reaction of penta-O-aceeyl-beta-D-glucose 1 with substituted phenols in the presence of boron trifluoride. Yields of the purified products varied from 52-85%. Benzyl alcohol could also be glucosylated using similar conditions. All products were purified by crystallization from ethanol. The purity and the anomeric configuration of the products were determined by means of H-1 and C-13 NMR spectroscopy melting points and optical rotation.

K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad-380 008, Gujarat, India Sheth P.T. Arts and Science College, Godhra-389 001, Gujarat, India Matushri Virbaima Mahila Science and Home Science College, Rajkot-360 007, Gujarat, India Manuscript received 05 October 2010. accepted 18 August 2011 Titled homologous series, methyl-p-(p'-n-alkoxycinnamoyloxy)cinnamates is synthesized and studied with a view to understand the relation between molecular structure and mesogenic property. First and second member of the series are nonmesomorphic. Third, fourth, fifth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth members of the series are enantiotropic nematic without exhibition of any smectic property even in the monotropic condition. Odd-even effect is not appeared in nematic-isotropic transition curve. Solid-isotropic or solid-nematic transition curve falls from first to fourth member of the series and follows zig-zag path of rising and falling up to fourteenth homologue and further falls to the sixteenth member of the series. Nematic-isotropic transition curve initially rises and then falls in a normal manner. Transition temperatures are observed through hot stage polarizing microscope. Nematic mesophase is of threaded, type of texture in all the derivatives. Average thermal stability is relatively higher and series is of middle ordered melting type. Mesomorphic properties are compared with structurally similar homologous series. Analytical data support the structure of the molecules.

Strong dipole moments have been built into two hexa-peri-hexabenzocoronene (HBC) derivatives (1 and 2) originating from the push-pull structure of the molecules with one electron-donating and one electron-withdrawing substituent. The influence of dipole moment on the self-assembly of HBCs in solution and in bulk has been investigated. Chemical Communications

The phase transition behavior of the liquid crystal dimer alpha,omega-bis(4,4'-cyanobiphenyl)nonane (CBC9CB), which has been reported to exhibit a nematic-nematic phase transition, has been investigated by means of high-resolution adiabatic scanning calorimetry. This nematic-nematic phase transition is weakly first-order with a latent heat of 0.24 +/- 0.01 kJ kg(-1). Mixtures up to 40wt% with 4-pentyl-4'-cyanobiphenyl (5CB) liquid crystals have also been investigated, which also show this nematic to nematic phase transition. The transition stays weakly first-order with a decreasing latent heat with increasing concentration of 5CB. For mixtures with more than 40 wt % uniaxial nematic-unknown nematic phase transition was not observed. ispartof: Physical Review E, Statistical, Nonlinear and Soft Matter Physics vol:84 issue:4 ispartof: location:United States status: published

Sheth P. T. Arts & Science College, Godhra-389 OOI, Gujarat, India Matushri Virbaima Mahila Science & Home Science College, Kalavad Road, Rajkot-360 007, Gujarat, India Manuscript received 23 November 2006, revised 5 May 2008, accepted 6 May 2008 A new homologous series of liquid crystals viz. 4-(4'-n-alkoxy benzoyloxy)-3-chlorophenylazo-4"-acetylbcnzenes are studied with a view to understand mesomorphic characteristics of the molecule. The nematic mesophase appeared as threaded type of texture. The first five and sixteenth homologues are nonmesomorphic. Mesomorphic property commences from the sixth member of the series as nematic type without exhibition of any smetic property. Transition temperatures are observed through hot stage polarizing microscope. Analytical data supports the structure.

Nonmesogenic 2,3,12,13-tetra-bromo-5,10,15,20-tetra-kis(4-butoxy-phenyl)- porphyrin crystallizes as the title 1,2-dichloro-ethane solvate, C60H58Br4N4O4�C2H4Cl2. The porphyrin ring shows a nonplanar conformation, with an average mean plane displacement of the ?-pyrrole C atoms from the 24-atom (C20N4) core of �0.50 (3) �. The 1,2-dichloro-ethane solvent is incorporated between the porphyrin units and induces the formation of one-dimensional chains via inter-halogen Cl?Br and butyl-aryl C - H?? inter-actions. These chains are oriented along the unit-cell a axis, with the macrocyclic ring planes lying almost parallel to the (010) plane. The chains are arranged in an offset fashion by aligning the butoxy chains approximately above or below the faces of the adjacent porphyrin core, resulting in decreased inter-porphyrin ?-? inter-actions, and they are held together by weak inter-molecular (C - Br??, C - H?? and C - H?Br) inter-actions. The nonplanar geometry of the macrocyclic ring is probably due to the weak inter-porphyrin inter-actions induced by the solvent mol-ecule and the peripheral butoxy groups. The nonplanarity of the mesogens could influence the mesogenic behaviour differently relative to planar porphyrin mesogens. � 2008 International Union of Crystallography.

Sheth P. T. Arts & Science College, Godhra-389 001, Gujarat, India E-mail : vrp181968@yahoo.co.in Matushri Virbaima Mahila Science & Home Science College, Kalavad Road, Rajkot-360 007, Gujarat, India Manuscript received 22 May 2007, accepted 22 August 2007 A new homologous series of liquid crystals viz. 4-(4'-n-alkoxy benzoyloxy)-napthylazo-4"-acetylbenzenes comprising eleven mesogens have been synthesized. The first four members of the series are non-mesogenic while nematic mesophase commences from fifth member of the series. Polymesomorphism occurs in eighth, tenth and twelfth member of the series. Only smectic mesophase occurs in fourteenth and sixteenth member of the series. The usual odd-even effect is observed in nematic-isotropic transition curve. The smectic-isotropic transition curve rises and falls smoothly as the series is ascended in usual manner. The mesomorphic range is wide. The thermal stabilityand mesomorphic characteristic are compared with structurally similar homologous series. Analytical data support the structure of molecules. It is middle ordered melting type with threaded texture of nematic phase and focal conic fan shaped texture of smecticmesophase.

A series of new thermoplastic polyesters based on 3,4-ethylenedioxythiophene (EDOT) with flexible aliphatic spacers have been synthesized and characterized for the first time. The thermal properties of these polyesters based on EDOT are comparable to those of conventional polyesters based on the 1,4-phenyl unit, indicating that EDOT is a viable replacement for the phenyl units. The glass-transition and melting-transition temperatures decrease monotonically with an increase in the spacer length. Theoretical calculations have revealed that the core angle for EDOT is comparable to that of unsubstituted thiophene and hence should be compatible with the formation of the mesophase. This has been confirmed experimentally by the synthesis of a main-chain, thermotropic, liquid-crystalline polyester based on EDOT that exhibits fluid birefringence. In fact, this is the first report in which a main-chain, liquid-crystalline polymer based on 3,4-disubstituted thiophene has been successfully designed and synthesized. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3479–3486, 2006

The synthesis and thermotropic properties of four homologous series of salicylaldimine-based dimer liquid crystals are reported. Two 4-(4-alkoxy-2-hydroxybenzylideneamino) benzoyloxy groups are connected to a central part consisting of a 1,3-phenylene, 1,5-pentylene, 2,2-dimethyl- 1,5-pentylene or 3,3-dimethyl-1,5-pentylene unit. The terminal alkoxy chains have been varied from 4 to 16 carbon atoms in length. All the compounds exhibit liquid crystalline phases whose behaviour depends on the nature of the central part and the length of the alkoxy terminal chains. All compounds of the series with the central phenyl part exhibit enantiotropic B-phases, and the sequence B-6 - B-1 - B-2 on increasing terminal chain length was observed. Replacement of the phenyl group with a pentyl central group partly suppresses the formation of B-phases. The longer homologues of this series show the B1 phase, while the shorter exhibit an intercalated SmCc mesophase. The introduction of methyl substituents to the pentyl spacer causes the melting points to fall dramatically and the formation of B-phases is totally suppressed. The compounds with the long tails show intercalated SmA(c) phases and those with short tails show intercalated SmCc phases.

Individual molecular tilt angle behavior in the smectic C region is represented upon application of a molecular statistical model to the polymorphic terepthal-bis-butylaniline (TBBA) in conjunction with the experimental layer spacings from SAXS measurements using the synchrotron X-ray beam. In the smectic A and smectic H phases of the mesogen, the order parameter fluctuations and pre-transitional effects responsible for sharp changes in the layer spacing and scattered intensities near the phase transition temperature are corroborated with varying positron annihilation lineshapes as a result of electron density fluctuations. ? 2002 Published by Elsevier Science Ltd.

Stereospecific formation of aryl 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside was achieved by reaction of penta-O-aceeyl-beta-D-glucose 1 with substituted phenols in the presence of boron trifluoride. Yields of the purified products varied from 52-85%. Benzyl alcohol could also be glucosylated using similar conditions. All products were purified by crystallization from ethanol. The purity and the anomeric configuration of the products were determined by means of H-1 and C-13 NMR spectroscopy melting points and optical rotation.

A chiral rigid moiety which forms the basis of a new class of non-amphiphilic carbohydrate liquid crystals has been developed. This moiety contains a fully intact glucopyranose ring embedded in a trans-decalin structure. The original carbohydrate is substituted so that only two hydroxyl groups are left, resulting in derivatives with reduced hydrophilicity. The substituents R and X-R' on the 4,6-O-ylidene beta-D-glucopyranoside are in the equatorial position and can be varied extensively, using straightforward synthetic procedures. Investigations as to the requirements for R and X-R' for inducing liquid-crystalline behavior have shown that at least one of the substituents should contain a large, polarizable aromatic moiety. An aromatic Schiff base fulfils this requirement.

Applied Chemistry Department, faculty of Technology & Engineering, M. S. University of Baroda, Baroda-390 001 Manuscript received 29 December 1992, accepted 9 March 1993 Liquid crystal formation in eight binary systems are reported in which one or both the components are non-mesogens. The binary systems of non-mesogens, comprising of components with terminal nitro or chloro substituent, exhibit induced smectic or nematic mesophases; induction of mesophase is higher in magnitude for a nitro group as compared to a chloro group. Shorter alkyl/alkoxy chains are not conducive to the mixed mesomorphism, probably due to lack of marked depression in melting points. The systems incorporating a monotropic mesogen and a non-mesogen, exhibit mesomorphic properties comparable with the binary systems of non-mesogens of the present work. Some of the binary compositions exhibit smectic phase at ambient temperature on cooling. The latent transition temperatures for non-mesogens are obtained and the phase diagrams are discussed in detail.

P. GChemistry Department, M. L. V. College, Bhilwara-311 001 Manuscript received 7 April 1987, accepted 11 August 1987 A new homologous series p-(p′-n-alkoxycinnamoyloxy)benzyiidene-p''-n-propoxy-anilines has been synthesised and its mesomorphic characteristics have been studied. It is a high melting series and exhibits rich mesomorphism. The range over which mesomorphic order prevails varies between 86° to 150°. The nematic isotropic transi­-tion curve shows odd- even effect. Polymesomorphism is also exhibited by the series, beginning from the seventh homologue with the appearance of smectic mesophase at about 125°. The S — N transition curve rises in a smooth fashion enhancing the smectic mesophase range at the cost of nematic mesophase length. Extrapolation of the smectic -nematic transition curve to the left, in keeping with its smoothness, makes it possible to determine the latent transition temperatures. The nematic mesophase shows a threaded texture while the smectic mesophase exhibits a focal conic fan-shaped smectic'A' texture.