Mesomorphism dependence on molecular rigidity and substitution of same functional group on lateral or terminal position of tailed phenyl ring

Novel liquid crystal materials (LCs) of low temperature range (53°C to 75°C) have been synthesized through a series of chalconyl derivatives consisting of two phenyl rings bonded through a –CH?CH?CO? central bridge to study the effect of molecular structure on LC properties in general and with a focus on molecular rigidity. The novel homologues series (C₁ to C₁₈) consists of thirteen homologues with general formula RO?C₆H₄?CH?CH?CO?C₆H₄?OC₁₀H₂₁(n) (meta). The C₁, C₂, C₃ homologues are nonliquid crystals (NLC) and the rest of the homologues (C₄ to C₁₈) are either monotropic or enantiotropic liquid crystals. C₄ to C₆ homologues are enantiotropicnematic and the rest of the mesomorphic homologues are (C₇ to C₁₈) monotropicsmectic in addition to monotropicnematic character. Transition and melting temperatures including textures of homologues were determined by an optical polarizing (POM) microscopy equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren, and that of the smectic phase are of the type Smectic A or C as judged directly from the heating top of the microscope. Thermal stability for smectic is very poor and of the nematic is (N-I) 69.3°C whose, total mesophase length ranges between 07.0 to 14.0°C at C₈ and C₄ homologues respectively.     

Synthesis and Liquid Crystal Behavior of a Novel Ester Homologous Series

A novel ester homologous series of 4-[4’-n-alkoxy cinnamoyloxy] benzyl benzoates has been synthesized. The series consists of 12 homologues. Liquid crystal properties commence from the sixth member to the last member of the series with the exhibition of an enantiotropic nematic phase without the exhibition of any smectogenic mesophase. The remaining homologues do not exhibit liquid crystal behavior. The texture of the nematic phase is of the threaded or Schlieren type. The solid-nematic or isotropic transition curve adopts a zigzag path and the nematic-isotropic transition curve steeply rises and then falls in the phase diagram and behaves in normal manner. An odd–even effect is absent in the nematic-isotropic transition curve with an alteration of transition temperatures. The average thermal stability for the nematic mesophase is 153.1°C, and the nematogenic temperature ranges vary from 12°C to 50°C. Analytical data confirm the molecular structures of the homologues. The Liquid Crystal properties and transition temperatures were observed through an optical polarizing microscope, equipped with a heating stage. The mesomorphic characteristics of the novel ester series are compared with other, known and structurally similar series. The novel series is predominantly nematogenic with the absence of any smectogenic character, with relatively short mesophase temperature ranges and of the middle ordered melting type.     

Mesomorphism Dependence of Molecular Flexibility with Reference to Bromo Tail Group

Halogenated chalconyl derivatives of novel homologues of esters are synthesized and studied with a view to evaluate their liquid crystal (LC) properties and their dependence on molecular structure with reference to molecular rigidity and flexibility. Novel homologous series of chalconyl esters comprises 12 homologues. All the members of a series are enantiotropically smectogenic. Nematogenic mesophase is missing throughout the series. Textures of smectic phase are of type A or C, as judged either by observing directly the sample homologue through polarizing microscopy or some selected members of the series by miscibility method. Transition temperatures were observed through an optical polarizing microscope equipped with a heating stage. The Cr-Sm transition curve adopts zigzag path and behaves in a normal manner. Sm-I transition curve exhibits an odd-even effect and behaves in a usual established manner. The average thermal stability for smectic is 154.79°C, and the mesogenic phase length range is from 5.1 to 24.4°C. The LC properties of the novel series are compared with structurally similar other known series. Thus, present novel series is fully smectogenic with middle ordered melting type and short range of liquid crystallinity.     

Mesomorphism dependence on molecular rigidity with reference to ‒CH˭CH‒ unit of central bridge

A novel ester homologous series of rich mesomorphism and low temperatures with unexpected phase behaviors of eleven homologues was synthesized and studied with a view to understanding and establishing the relation between mesomorphic behaviour and the molecular structure of a series 4-(4′-n-alkoxybenzoyloxy)-4″-chlorobenzyl cinnamates. All the members of the novel series are enantiotropically smectogenic and the octyloxy (C₈) to hexadecyloxy (C₁₆) homologues are enantiotropically nematogenic, in addition to smectogenic. Odd–even effect is observed for Sm?I/Sm?N transition curve but it is absent for N?I transition curve. Textures of nematic phase are threaded or Schlieren and that of the smectic phase are fan shaped or batonates of smectic-A type phase or Smectic-C type for C₁₆ homologues as judged directly from a heating stage of an optical polarizing microscopy. Analytical and spectral data confirmed the molecular structures of novel homologues. Mesomorphic properties of present series are compared with the structurally similar other known series. The average smectic and nematic thermal stabilities are 92.78°C and 100.8°C, respectively. Mesophase length minimum to maximum for smectic and nematic are 21.0°C to 31.1°C and 8.4°C to 42.6°C respectively. Thus, the present novel series is partly nematogenic and fully smectogenic with considerable degree of mesomorphism and low melting type.     

Mesomorphism dependence on heterocyclic tail

A novel homologous series of liquid crystal materials containing a heterocyclic ring was synthesized with a view to understanding and establishing the relation between liquid crystal (LC) properties and a molecular structure; and with a view to curing skin-related diseases following biological activity studies. The series consist of 13 (C₁ to C₁₈) members. All the members are liquid crystals. The C₄ to C₁₈ members are smectogenic of which C₄ and C₅ are monotropic and remaining members (C₆ to C₁₈) are enantiotropic in nature; whereas all C₁ to C₁₈ members are enantiotropically nematogenic. Hence the C₁, C₂, C₃ members are only nematogenic and the rest of the homologues are smectogenic in addition to nematogenic. Transition temperatures were determined by an polarizing optical microscope equipped with heating stage. Analytical and spectral data confirmed the molecular structures of homologues. It is a middle ordered melting type series. LC properties of a series are compared with the structurally known series.     

Low frequency relaxation in liquid crystals in relation to structural relaxation in glass-formers

Liquid crystals (LC) are the state of matter intermediate between isotropic liquids and the crystalline state. LC-forming molecules have strongly anisotropic shapes (rod-like in most cases). This leads to an interaction potential that consists of distance-dependent and orientation-dependent parts. Rotational dynamics of LC molecules falls into two frequency regions. Rotations about the short axes are strongly hindered by the potential barrier and thus coupled to fluctuations of the molecular centers of mass. This in turn causes these longitudinal or “flip-flop” motions, characterized by a relatively large relaxation time τ_||, to exhibit considerable temperature, pressure and volume dependences. Experimental relaxation times determined to date for various LC phases (nematic, smectic A, C, and E) for different thermodynamic conditions (isobaric, isothermal and isochoric) are discussed herein, adopting the formulae applied for characterization of the structural relaxation times of glass-formers (GF). This analysis appears fruitful; in particular, the strength parameter characterizing the steepness of the interaction potential can be determined from the relaxation times, and τ_|| is independent of temperature and pressure along the nematic-isotropic transition line, similar to the behavior of the structural relaxation time along certain transitions in GFs.     

Fabrication of a fast-switching liquid crystal device using reactive self-assembled polyimide alignment layer

ABSTRACT

We proposed a new vertical alignment method for simultaneously improving the alignment force and electro-optical properties. The key point of the new method is the self-assembly of the reactive monomer via hydrogen bonding with the polyimide alignment layer and the formation of pre-tilt using the reactive monomer on an alignment layer. Through the self-assembly of the reactive monomer and the generation of the pre-tilt, it is possible to obtain a higher alignment force and a fast response time. As a result, through a simple additional step, we can fabricate a fast-switching liquid crystal device using a reactive self-assembled alignment layer.     

Synthesis of Some Novel Aromatic Alkynyl Silanes: Mesomorphic Characterization of Ethynyl-Substituted Rod-Shaped Molecules

The synthesis and characterization of 10 new rod-shaped substituted benzoates possessing the 4-(2-trimethylsilyl)ethynyl group in terminal phenyl position is reported employing the simple and efficient Sonogashira cross-coupling and DCC esterification. 4′-Dodecylbiphenyl-4-carboxylic(2-trimethylsilylethynyl)-phenyl ester (3i), 4-(4′-hexadecyloxybenzyloxy) carboxylic-4-trimethylsilanylethynyl-phenyl ester (3j), and 1,4-bis(4-(pentyloxy)phenyl)buta-1,3-diyne (7) compounds were evaluated for liquid crystal property.

[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]     

Influence of a.c. Electric Field on Infrared Absorption Spectra of Liquid Crystals and Determination of Orientational Order Parameter by Infrared Dichroism. II. Molecules with Weak Negative Dielectric Anisotropy

The influence of a.c. electric field (10 kHz) on the IR spectra of the nematic phase of six p-alkoxybenzylidene-p,n-butylanilines with weak negative dielectric anisotropy was studied and the temperature dependence of the orientational order parameter and threshold voltage have been investigated. The values of band elastic constants K₃₃ were calculated for MBBA and EBBA.     

ENDOR Study of the Phase Transition in Benzil

ENDOR spectroscopy was used to elucidate the domain structure of benzil accompanying its phase transition at 84°K. Spectral twinning was observed on a single-crystalline sample as a result of multidomain formation below the phase transition temperature. This twinning was explained by applying the Landau theory of phase transitions. With knowledge of the anisotropy of the proton hyperfine interaction, we extracted the angle between the domains and the morphologic two-fold axis to be 1.55° at 2°K.