A. V. Doshi

Determination of Latent Mesogenic Behavior in Nonmesogenic Compounds by Extrapolation Method

A homologous series of 8-(4′-n-alkoxybenzoyloxy) quinolines were synthesized by established methods [5,6]. On evaluation by optical microscopy, none of the homologues were found to exhibit mesogenic behavior even in the monotropic condition. Then, each homologue (B) was mixed with a liquid crystal component (A) and binary systems were studied by optical microscopy. Solid–mesomorphic or isotropic–nematic transition temperatures of binary mixtures were determined and plotted to obtain the phase diagram for transition temperatures versus percentage composition of component (A). The nematic–isotropic transition curve was extrapolated to zero mole percentage of component (A) (100%B) to determine the latent transition temperature (LTT) of each nonmesomorphic homologue. The number of carbon atoms in the n-alkyl chain of each homologue versus LTT is plotted and a phase diagram is obtained. The isotropic–nematic transition curve behaves in a normal manner like a curve behaving for a typical nematogenic homologous series, including odd–even effects in its phase diagram. This method is useful to determine the probable temperature at which a nonmesogenic substance can show mesogenic behavior, provided a suitable condition is applied. Also, it is useful to correct the LTT of a homologue from the mesomorphic–isotropic transition curve.

Determination of Latent Transition Temperatures of Nonmesomorphs by Extrapolation Method in Binary Systems

Eight binary systems consisting of mesomorphs and nonmesomorphs (A1 or A2, + B1, B2, … B7, B8) were studied with a view to determine the latent transition temperature (LTT) for the nonmesomorphic component (B) of a binary system by an extrapolation method. Encouraging results supporting earlier views and LTT values were obtained for seven binary systems. Instead of reporting a single value of LTT, the range of temperature or two or three values are reported herewith depending upon the possible paths of extrapolation. LTT reported earlier for nonmesomorphs lie within the range of temperature determined presently. Though the “group slope value” differs from the earlier reported value, the group efficiency order remains the same. Thus, the present investigation raises the credibility of an extrapolation method to determine LTT and group efficiency order for nematic mesophase. Component A1 and A2 are nematogenic, namely, p-(p′-n-propyloxy benzoyloxy) anisole (A1) (90.0 to 116.0) and p-(p′-n-butyloxy benzoyloxy) anisole (A2) (116.0 to 105.5). B1 to B8 are Schiffs bases. Transition and melting temperatures are observed through hot stage polarizing microscope for binary mixtures and pure components.

Synthesis and Mesomorphism of Novel Liquid-Crystalline Isobutyl-p-(p′-n-Alkoxy Cinnamoyloxy) Cinnamates

A new homologous series viz. Isobutyl-p-(p′-n-alkoxy cinnamoyloxy) cinnamates consisting of 11 homologs has been synthesized with an isobutyl cinnamate end group and a further cinnamate moiety as a linking group. The methyl to butyl homologs are nonmesomorphic, and the pentyl to hexadecyl derivatives are enantiotropic nematogens without exhibition of any smectic phases. The average thermal stability for the nematic phase is 138.1°C with a middle ordered melting point. The structures of the novel materials were confirmed by spectroscopic techniques. The liquid crystal phase type was determined by optical polarizing microscopy and all textures are of the threaded type. The mesomorphic behavior of the series is compared with a structurally similar homologous series.

Study of Liquid Crystalline State and Evaluation of its Properties Through a Novel Homologous Series

A novel homologous series α-4-[4′-n-alkoxy benzoyloxy] benzoyl-β-3″,4″-dimethoxy phenyl ethylenes has been synthesized and studied for liquid crystal (LC) properties to understand and establish the relation between molecular structure and liquid crystalline behavior. Twelve members of series were synthesized. All the members except first member of the series are mesomorphic. The hexyloxy to tetradecyloxy homologoues are smectogenic and nematogenic in character. The ethoxy to pentyloxy and the hexadecyloxy homologues exhibit only nematogenic character with the absence of smectogenic mesophase formation. An odd–even effect is observed for the smectic-nematic and the nematic-isotropic transition curves in the phase diagram. The smectic mesophase showed as either the SmA or SmC. The nematic mesophase shows a threaded or Schlieren type texture. Spectral and analytical data confirms the molecular structures of the homologues. The thermal stabilities for the smectic and the nematic are 115.6°C and 156.6°C. The smectogenic and nematogenic mesophase length vary from 7°C to 28°C and from 7°C to 52°C respectively. The transition temperatures were observed through an optical polarizing microscope equipped with heating stage. Thus, the presently investigated novel homologous series is predominantly nematogenic and partly smectogenic with a middle ordered melting type and a considerable mesophase length. The LC properties of the novel series are compared with structurally similar homologous series.

Homologous Series of Azomesogens: 4-(4′-n-Alkoxy Benzoyloxy)-3-Chloro Phenylazo-2″-Chlorobenzenes

The increasing demand of liquid crystalline materials in various fields of applications has inspired the present investigation. A mesogenic homologous series, 4-(4′-n-alkoxy benzoyloxy)-3-chloro phenylazo-2″-chlorobenzenes, of twelve homologues has been synthesized. All the members of the series are either monotropically or enantiotropically mesogenic except the first member of the series. The nematic mesophase commences from the ethyl derivative and goes to the dodecyl derivative of the series. Tetradecyl and hexadecyl derivatives show a monotropic smectic phase. The nematic mesophase shows a threaded texture, while the smectic mesophase shows a focal-conic-fan-shaped texture. Polymesomorphism is not displayed by any member of the series. The solid-isotropic or solid-mesomorphic transition curve follows a zigzag path of falling and rising tendency as the series is ascended. The usual odd–even effect is observed in the nematic–isotropic transition curve with alternation of transition temperature. Transition temperatures are observed through a polarizing microscope with a heating stage. Analytical data support the structure of the molecules. The average thermal stability and mesomorphic properties of the series are compared with structurally similar other homologous series. Group efficiency order for the smectic and the nematic phases is suggested.

Mesomorphism of Binary Systems of Nonmesogenic Compounds

Three binary systems, each consisting of two nonmesogenic compounds, viz. p-tolual-p-phenetidine (M.P. 108.5°C) [A] as the common component, and Methyl p-(p′-n-butyloxy benzoyloxy) benzoate (M.P. 119.0°C) [B1], Ethyl-p-(p′-n-butyloxy benzoyloxy) benzoate (M.P. 94.0°C) [B2], and n-Butyl p-(p′-n-butyloxy benzoyloxy) benzoate (M.P. 130.0°C) [B3] as the second component, respectively, are studied with a view to understand the effect of terminal groups on nematic and/or smectic mesomorphism. Latent transition temperatures (LTT) of the constituent components A, B1, B2, and B3 were determined by extrapolation. Binary system (A + B1) induces a nematogenic mesophase while binary systems (A + B2) and (A + B3) both induce a smectic mesophase in addition to a nematic mesophase. Phase diagrams of the binary systems under investigation are plotted for the mole percent of component (A) versus the transition temperatures of each binary system as determined from polarizing optical microscopy. The texture of the nematic mesophase is of threaded type and that of the smectic mesophase is focal-conic fan shaped of the type smectic-A. Components A, B1, B2, and B3 were prepared by established methods. Analytical data support the structure of molecules under investigation. Melting points of the constituent components match with data reported earlier.

Synthesis and Mesomorphism of Novel Liquid Crystalline: p-(p′-n-Alkoxy Benzoyloxy) Methyl Cinnamates

A new homologous series p-(p′-n-alkoxy benzoyloxy) methyl cinnamates is synthesized with a view to understand and establish the relation between mesogenic properties and structure of molecules. Ethyl to octyl, decyl, dodecyl, tetradecyl, and hexadecyl homolgues are enantiotropically nematogenic, while the methyl homologue is nonmesogenic. None of the homologues exhibit a smectogenic mesophase. An odd–even effect is observed in the nematic–isotropic transition curve. The average thermal stability is 105.0°C and the nematogenic mesophase ranges from 11.0°C to 54.0°C. Thus, the series is of a middle ordered melting type with moderate nematogenic range. Analytical data confirm the structure of the compounds, and the mesomorphism was identified by optical microscopy. The mesogenic properties are compared with structurally similar compounds.

Dependence of Molecular Structure on Mesomorphic Behavior with Special Reference to Central Bridge

A novel homologous series of liquid crystalline 4-(4′-n-alkoxy cinnamoyloxy)-4″-methoxy benzyl cinnamates was synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal behavior. The series consists of eleven members of the series. None of the homologue derivatives are either nonliquid crystal or smectogenic, i.e. all the eleven members of the novel homologous series are enantiotropcially nematogenic only. Transition and melting temperatures as well as textures of the nematic mesophase were determined on an optical polarizing microscope equipped with a heating stage. The transition curves of the phase diagram show phase behavior in a normal expected manner. An odd-even effect is observed for the nematic-isotropic transition curve. The textures of the nematic mesophase are threaded or Schlieren as determined a by miscibility method. Analytical and spectral data confirm the molecular structures of the homologues. The average thermal stability for nematic is 213.8°C. The isotropic temperatures vary between 190°C and 240°C. The nematogenic mesophase length varies from 17°C to 102°C. Thus, the novel homologous series is entirely nematogenic without the exhibition of smectogenic character. The liquid crystal (LC) properties of the present novel series are compared with structurally similar other known homologous series.

Synthesis and Study of Novel Liquid Crystalline Homologous Series: 4-(4′-n-Alkoxy Benzoyloxy)-3-Methoxy Phenyl azo-3″, 4″ Dichlorobenzenes

The synthesis and mesomorphic properties of a new homologous series of azomesogens, 4-(4′-n-alkoxy benzoyloxy)-3-methoxy phenyl azo-3″,4″ dichlorobenzene is detailed. The first four members of the series are nonmesomorphic, and the other eight members are smectogenic in character. The smectic mesophase, which is exhibited montropically, commences from the pentyl to the hexadecyl derivatives. The usual odd-even effect is observed in the isotropic-smectic transition curve. The isotropic-smectic transition curve behaves in a normal manner. The smectic mesophase shows a focal conic fan shaped texture of the smectic A type. An important feature of the series is the absence of the nematic property. The thermal stability and mesomorphic characteristic are compared with two structurally similar homologous series.

Synthesis and Mesomorphism of Novel Liquid Crystalline: 4-(4′-n-Alkoxy Benzoyloxy)-Naphthylazo-4″-Chlorobenzenes

A new azoester homologous series 4-(4′-n-alkoxy benzoyloxy)-naphthylazo-4″-chlorobenzenes is synthesized. Its first and second homologues are nonmesomorphic, while the rest of the homologues are mesomorphic, showing enantiotropic nematic behavior. Smectic character is totally absent. An odd–even effect is observed in the nematic–isotropic transition curve with alternation in transition temperatures. The average thermal stability and liquid crystal behavior for the nematic mesophase are compared with structurally similar homologous series. Analytical data support the structures of the molecules. The texture of the nematic mesophase is of threaded type. Transition temperatures are observed through hot-stage polarizing microscope. Analytical data support the structures.