A. K. Prajapati

Mesogenic properties and the effect of 1,2,4-trisubstitution on the central benzene nucleus of a three-ring mesogen

Four mesogenic homologous series have been synthesized by fixing a rigid 4-substituted phenylazo group to a resorcinol moiety. In series I and II, one phenolic -OH group is esterified by 4-n-alkoxybenzoyl groups; in series III and IV both the phenolic -OH groups are esterified by 4-n-alkoxybenzoyl groups. All the homologues of series III and IV exhibit low melting smectic C phases. Monoesters of series I and II, having free lateral hydroxy group with strong hydrogen bonding, exhibit high temperature nematic phases. The effect of different substituents on mesomorphic properties is discussed. One homologue of series III was doped with a chiral dopant and its spontaneous polarization evaluated.

Effect of Lateral Hydroxy/Alkoxy Group on Mesomorphism of Azobenzene Derivatives

Abstract Two homologous series are synthesized by fixing a rigid 4-methyl phenyl azo group to resorcinol moiety. In series I one phenolic -OH group is alkylated whereas, in series II both the phenolic -OH groups are alkylated. Monoethers of series I having free lateral hydroxy group due to strong hydrogen bonding, exhibit nematic mesophases whereas, diethers of series II are non-mesogenic.

Effect of a lateral methyl group on azo-mesogens containing the naphthalene moiety

Two mesogenic homologous series, 2-[4-(4-n-alkoxybenzoyloxy)-2-methylphenylazo]-naphthalenes (I) and 2-[4-(4-n-alkoxybenzoyloxy)-3-methylphenylazo]naphthalenes (II) with a lateral methyl group have been synthesized. Both series are purely nematogenic. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effect of the lateral methyl group on mesomorphism. The chiral nematic (N*) mesophase was induced in the system by doping with a derivative of naturally occurring chiral menthol.

Oil Solubilization Capacity, Liquid Crystalline Properties, and Antibacterial Activity of Alkanolamine‐Based Novel Cationic Surfactants

A series of monomeric and dimeric cationic surfactants with tuned polarity was synthesized. Oil solubilization capacity, thermotropic liquid crystalline properties, and minimum inhibitory concentration (MIC) of novel hydroxylated cationic surfactants using selected gram positive and gram negative bacteria were examined. Antibacterial activity and the propensity of gemini surfactants for oil solubilization were observed to be better than those of corresponding monomeric surfactants. Pseudo ternary phase diagrams for these surfactants, methyl methacrylate (MMA), and water clearly showed, that microemulsions can be easily formulated with all these surfactants. Solubilization and foam studies of mixed surfactant systems were also examined. Molecular architecture like the tail length, head group area, and presence of ethanolic goups in the surfactant affect the performance properties. Unlike conventional gemini surfactants the synthesized gemini surfactants also show thermotropic liquid crystalline properties (smectic‐A, Lα phase).

T-shaped non-symmetrical twin liquid crystalline compounds

New unconventional T-shaped non-symmetrical dimeric liquid crystalline compounds have been synthesised and their thermotropic properties studied on the hot-stage of a polarising microscope. These compounds consist of an azo-ester mesogenic unit with a range of terminal substituents (–CH3, –OCH3, –NO2 or –Cl) at one end, interconnected by a flexible spacer (nu2009=u20094, 5 or 10) via ether and ester linking units to a biphenyl moiety at the lateral hydroxyl position of the azo-ester. All the compounds were characterised using a combination of elemental analysis and standard spectroscopic methods. The compounds were found to exhibit enantiotropic nematic and smectic mesophases. The effect of different terminal substituents on mesomorphism is discussed.

Synthesis of a new mesogenic homologous series containing naphthalene moiety

Abstract A new series of mesogenic Schiff′s base esters, 4-(4′-n-Alkoxybenzoyloxy) 3-methoxy benzylidene 2”-aminonaphthalenes has been synthesized. The synthesized compounds were characterised by elemental analysis and standard spectroscopic methods. All the homologues synthesized exhibit mesomorphism. The mesomorphic properties of the present series are compared with other structurally related series. Chiral nematic mesophase (N*) is induced in the system by doping a derivative of naturally occurring chiral compound.

H-shaped azoester-oxymethylene containing twin liquid crystalline compounds

Two mesogenic homologous series of H-shaped symmetrical dimers were synthesised and their thermotropic properties studied by differential scanning calorimetry and on a hot-stage of a polarising microscope. These compounds consisted of two mesogenic units of azoester interconnected through tetramethylene flexible spacers (nu2009=u20094) by ether linkage resulting in the structure of ‘H-shaped’ dimeric compounds. The difference between the two series was in the structure of terminal substituents (–CH3 for series I and –OCH3 for series II) attached on the azoester mesogens at one terminus. All these compounds were found to be smectogenic. The mesomorphic properties of the series were compared with each other and with other structurally related mesogenic H-shaped dimers. The trans-azobenzene groups of the H-shaped dimeric compounds displayed a high-intensity π–π* transition at about 365 nm and a low intensity π–π* transition at around 470 nm, therefore photochromism can be achieved by the introduction of the azo linkage to the H-shaped dimeric compounds.

Effect of Terminal Branching on Mesomorphism

Abstract Two new mesogenic homologous series having following general structural formula have been synthesized. In series-I, n-octyloxy and n-dodecyloxy derivatives exhibit enantiotropic smectic A phase whereas n-decyloxy and n-tetradecyloxy derivatives exhibit monotropic smectic A phase, rest of the members are non-mesogenic. Looking to the terminally branched alkyl group smectogenic tendency of series-I is quite interesting. In series-II, all the members exhibit enantiotropic nematic phase. The smectic C mesophase commences from the n-heptyloxy derivative and is exhibited alongwith nematic phase till the last n-hexadecyloxy derivative studied. Though branching is known to be less conducive to mesomorphism, it is observed that entire series-II is mesomorphic in nature.

AZOMESOGENS CONTAINING TWO FUSED RING MOIETIES: SYNTHESIS AND CHARACTERIZATION

Several liquid crystalline compounds derived from 2-aminonaphthalene have been synthesized. The molecules are designed to accommodate two napthalene moieties. The molecular structures of these new compounds have been characterized by element analysis, FTIR, and NMR spectral studies. The mesomorphic behavior has been studied using mainly polarized microscope and in some cases differential scanning calorimeter as well. Our investigation reveals that all the compounds exhibit enantiotropic nematic phase. The mesomorphic behaviors of these new compounds have been compared with those of structurally related materials.

Induction of Chirality by Doping Mesogens with Non-Mesogenic Chiral Dopant

Abstract Use of chiral dopant in binary mixtures to induce ferroelectricity/chiral nematic phase is an easier way than the synthesis of ferroelectric or chiral nematic materials. Number of researchers have tried to induce chirality in the achiral mesogens by doping it with naturally occuring chiral compounds or their derivatives. Few binary systems were studied where one of the components is the non-mesogenic chiral dopant. In almost all the systems studied cholesteric phase (N) is induced with lowering in transition temperatures. The study provides means to induce chirality in mesogenic system by doping it with the derivative of naturally occurring chiral menthol.