Study of Y-shaped liquid crystalline materials with polar nitro substituent

A new homologous series of Y-shaped liquid crystals namely 4-Nitro-[2′4′bis (4″-n-alkoxybenzoyloxy)] phenyl bisazobenzenes have been synthesized and its thermotropic properties studied on the hot stage of a polarizing microscope. The compounds consist four phenyl rings joined through ester and bisazo linkages with alkoxy and nitro as terminal substituents. The structures of synthesized compounds were confirmed by spectroscopic techniques such as FTIR, ¹HNMR as well as elemental analysis. The compounds were found to exhibit enantiotropic nematic and smectic mesophases. The role of molecular shape, size and polarity of functional groups in the mesophases formation is discussed.     

Synthesis and Mesomorphic Characteristics of Fluoroaniline Derivatives with Different Lateral Groups

Two new homologous series of liquid crystals viz. 4-(4'-n-alkoxybenzoyloxy)-2-chlorophenylazo-4”-fluorobenzenes(I) and 4-(4'-n-alkoxybenzoyloxy)-2-methylphenyl azo-4”-fluorobenzenes(II) with terminal fluoro, lateral chloro(I) and methyl(II) group and central ester and azo linkages are synthesized and their mesomorphic properties are studied. Both the series are similar in molecular structure with the difference in their lateral substitutions; series I has chloro group and series II has methyl group as laterally substituted groups. All the twelve homologues of each of the series are mesogenic in nature. Series I shows nematic mesophase from the first C₁ to the last C₁₆ derivative synthesized; smectic mesophase is exhibited by last two viz. C₁₄ and C₁₆ derivative, where as all the members from C₁ to C₁₆ of series II only show nematic mesophase. The nematic mesophase shows marble texture and the smectic mesophase shows Schlirene texture of the Smectic C variety. Both the series are compared with structurally related series.     

Synthesis and Mesomorphic Characterisation of Chiral Homologues

Abstract

Chiral liquid crystals have attracted considerable interest as they exhibit a good variety of modulated phases. We have synthesised a homologous series viz., 4-(4^!-n-alkoxy benzoyloxy) benzylidene-4^!!?1-(s)-methyl propoxy anilines, incorporating a terminal chiral centre, inorder to obtain better understanding of the relationship between molecular structure and appearance of SmC* phase in the molecules. It is observed that, in the present series the lower members upto butyl are pure nematogens, while pentyl to hexadecyl derivatives exhibit classical smectic as well as nematic mesophases. An additional smectic C* phase is observed in the middle octyl to dodecyl homologues. The homologues have been characterised by IR, NMR and DSC. Their mesomorphic properties have been compared with structurally related homologous series.     

Synthesis,Characterization and Mesomorphic Properties of New Rod-like Thiophene Based Liquid Crystals

Two new mesogenic homologous series of Schiff base esters, 2-[4-(4′-n-Alkoxy benzoyloxy) benzylidenamino] 3-cyno thiophine (Series-A) and Schiff base cinnamates, 2-[4-(4′-n-alkoxy cinnamoyloxy) benzylidenamino] 3-cyano thiophene (Series-B), comprising a thiophene moiety were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as FT-IR, ¹H-NMR and ¹³C-NMR, and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry and optical polarizing microscopy. All the derivatives are mesomorphic in nature showing the nematic phase, and the higher members of Series-A show a smectic C phase whereas Series-B exhibits only the nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related compounds.     

Synthesis and mesomorphic properties of 2,4-bis(4′-n-pentyloxybenzoyloxy)- benzylidine-4″- n-alkoxyaniline

The synthesis and mesomorphic properties of a new series of 2,4-bis(4′-npentyloxybenzoyloxy)- benzylidine-4″ -n-alkoxyaniline (DC5An) are reported. The molecular structure of compounds was confirmed by FTIR, ¹H-NMR, ¹³C-NMR, mass spectroscopy and elemental analysis. The mesomorphic properties were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) measurements. All compounds of the series exhibit nematic (N) and smectic C (SmC) phases. The first four homologues (DC5A1-DC5A4) display a N mesophase, whereas the highest homologues (DC5A5-DC5A10) exhibit an enantiotropic dimorphism N and SmC phases. The mesomorphic properties of the present series are compared and discussed with other structurally related series.     

Mesogenic 3,6-bis(4-hydroxyphenyl)-1,2,4,5-tetrazine alkanoate esters

A novel series of 3,6-bis(4-hdroxyphenyl)-1,2,4,5-tetrazine alkanoate esters were synthesized and their mesogenic properties were studied using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The impact of changing the tail-core linkage from alkyl or alkoxy to ester is profound. Compared to the alkyl or alkoxy linkages, the ester linkage reduced mesogenic properties. Short-tailed compounds are non mesogenic (4a-4e), while long-tailed compounds (4f-4r) exhibit nematic phases. Unlike the alkyl or alkoxy tail series, none of the 18 presented esters in this series exhibits a smectic phase.     

Synthesis and study of mesomorphic properties in rod-like chalconyl compounds

In order to investigate the influence of the central linking group and effect on flexibility on mesophase behavior of liquid crystal we have synthesized newly homologous series viz. 3-(4-Octyloxyphenyl)-1-(4′-n-alkoxy phenyl) prop-2-en-1-one (Series-l) consists of thirteen homologues (C₁ to C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈). Textures of a nematic phases are threaded or Schlieren type. The textures of smectic and nematic phase are directly judged from the heating and cooling condition. Group efficiency order for mesophases is derived on the basis of thermal stabilities from the comparative study of thermometric data determined from structurally analogous series. A transition curve as depicted in a phase diagram behaves in normal manner. Structural and conformational characterization of these new compounds had achieved by ¹H NMR, ¹³C NMR, IR, and elemental analysis.     

Mesomorphism dependence of a terminal or lateral alkoxy group

A novel homologous series of thermotropic mesomorphs has been synthesized and studied with a view to understanding and establishing the effect of molecular structure on mesomorphic properties with reference to rigidity and flexibility of the homologues series: RO-C₆H₄-CH?CH-CO-C₆H₄-OC₁₈H₃₇(n). The novel homologous series comprises 13 novel homologues (C₁ to C₁₈), from which 11 homologues are enantiotropically mesogenic (C₃ to C₁₈). Smectogenic mesophase commences from C₇ homologue, and nematogenic mesophase is exhibited by C₃ to C₁₈ homologues in enantiotropic manner. Thus, C₇ to C₁₈ homologues are enantiotropically smectogenic plus nematogenic. Textures of smectic phase are of the type A or C, and that of nematic phase are threaded or Schlieren as confirmed through an optical polarizing microscope equipped with a heating stage. Transition curve of a phase diagram behaved in a normal manner except N-I transition curve, which shows minor deviating trend (C₁₂ to C₁₈) from expected normal behavior. An odd-even effect is exhibited by N-I and Sm-N transition curves. Analytical, spectral, and thermal data confirm the molecular structures of novel homologues. Thermal stabilities for smectic and nematic are 52.7°C and 66.6°C, respectively, whose total mesophase lengths range from 12.0°C to 28.0°C. Thus, novel series of chalcones is a low melting series whose mesogenic transition temperatures vary between 38.0 and 86.0°C.     

Mesomorphism Dependence on the Position of Substitution of a Pair of Esters

A novel homologous series of ethylene derivatives of thermotropic liquid crystals has been synthesized. The methoxy to octyloxy derivatives are nematogenic, the decyloxy to tetradecyloxy derivatives are smectogenic, in addition to nematogenic, and the hexadecyloxy homologue is smectogenic only. All the members of the series are enantiotropically mesogenic. Thermotropic behavior was determined by an optical polarizing microscope equipped with a heating stage and Differential Scanning Calorimetry (DSC) study. Analytical and spectral data confirm the molecular structures of homologues (infrared, nuclear magnetic resonance, mass spectra, X-ray, and DSC data). Textures of the nematic phase are threaded or Schlieren and that of smectic phase are focal conic fan-shaped of smectic A or C. Transition curves of the phase diagram behave in a normal manner except one or two deviations from the normal trend. The mesophase range (Sm+N) varies from 3°C to 44°C. The average thermal stability for smectic is 93°C and that for nematic 117.4°C. The LC behavior of the novel series is compared with a structurally similar known series.     

Synthesis of 1 - (4-Alkoxy or Alkyl- Benzoyloxy-Phenyl) - 2- (4′- Pentylphenyl) - Ethanes. Influence of the Central Group on the Mesomorphic Properties

An homologous series of mesomorphic compounds, the I-(4-alkoxy or alkyl-benzoyloxyphényl)-2-(4′-pentylphenyl)-ethanes, has been synthesized. The compounds with R = alkyl have low-melting points and wide mesomorphic ranges, for example from 33.5°C to 106.5C. The compounds with R = alkoxy exhibit a smectic polymorphism; for example a compound of this series is successively smectic B, F and C. The influence of the central linkage when the ethane group is replaced by an ester, single bond, ethylene, azomethine, azo, methylenecetone or cetone groups, is discussed.     

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.     

Synthesis and Evaluation of Liquid Crystal Behavior of a Novel Homologous Series: 4-(4′-n-Alkoxy benzoyloxy) Phenylazo-2″, 6″-dimethylbenzenes

A novel homologous series entitled 4-(4′-n-alkoxy benzoyloxy) phenyl azo 2^″, 6^″-dimethyl benzenes consisting of 12 members is reported. Liquid crystal behavior as a nematogenic mesophase commences from the pentyloxy homologue monotropically and then continues enantiotropically until the last hexadecyloxy homologue without exhibition of any smectogenic behavior. An odd-even effect is observed for nematic-isotropic transition curve of the phase diagram. The textures of the nematic mesophase are of the threaded or Schlieren type. Analytical and spectral data support the molecular structure of the homologues. Transition temperatures of the novel homologues were determined by an optical polarizing microscopy. Liquid crystal properties of a novel homologous series are compared with other known homologous series. The average thermal stability for the nematic phase is 77.1°C.     

Novel Cinnamate Esters—Synthesis and Mesomorphic Properties in Relation to Molecular Structure

A novel homologous series 4-[4′-n-alkoxy cinnamoyloxy] benzyl cinnamates consisting of 11 homologs was synthesized and studied with a view to understanding and establishing the relation between molecular structure and mesomorphic behavior of a substance. Mesomorphic behavior of the series commences from the third homolog and then continues until the last hexadecyloxy homolog. The first and second members of a series are non-mesomorphic. Nematogenic mesophase formation is observed from the propoxy homolog to the hexadecyloxy homolog, but the smectogenic mesophase formation is observed from the hexyloxy homolog to the tetradecyloxy homolog. All mesomorphic transitions are enantiotropic in nature. Transition temperatures were determined by an optical polarizing microscopy equipped with a heating stage. The textures of the nematic mesophase are threaded or Schlieren in type and that of the smectic mesophases are focal conic fan shaped of the smectic A or smectic C type. A phase diagram of the series shows a normal behavior of the transition curves with a minor abnormality of the last three homologs for the nematic-isotropic transition curve. The average thermal stability for smectic and nematic mesophases is 176.0°C and 219.3°C, respectively. Analytical and spectral data agree with the molecular structures of homologs. Mesomorphic phase length varies between 22°C and 76°C. Smectic phase length varies from 6°C to 33°C and nematic phase length varies from 22°C to 54°C. Thus, the novel present series is predominantly nematogenic and partly smectogenic. Mesomorphic properties of the novel series are compared with structurally similar other known homologous series.     

Study of the molecular structure on liquid crystal properties with reference to thermotropic azoester derivatives

An azoester homologues series: RO?C₆H₄?COO?C₁₀H₆?N?N?C₆H₄?OC₅H₁₁ (para) as novel liquid crystalline (LC) materials has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on LC properties with reference to laterally substituted phenyl ring and terminally substituted ?OR and ?OC₅H₁₁ (n) groups; including ?COO? and ?N?N? central bridges. Novel homologous series of thermotropic LC variety consists of thirteen homologues (C₁ to C₁₈). C₁ to C₃ derivatives are nonliquid crystal (NLC); C₄ is only nematogenic and C₅ to C₁₈ are smectogenic plus nematogenic. All the mesogenic homologues (C₄ to C₁₈) are enantiotropically nematogenic or/and smectogenic as confirmed by a polarizing optical microscopy (POM) equipped with a heating stage. Transition curves Cr-I/M, Sm?N, and N?I behaved in normal manner in a phase diagram. Odd-even effect is exhibited by Sm?N and N?I transition curves. Analytical, spectral and thermal data confirms the molecular structure of novel homologues. Novel azoester series is predominantly nematogenic and partly smectogenic whose mesogenic temperatures ranges minimum to maximum from 79.0°C to 162.0°C. Thermal stability for smectic and nematic are 128.2°C and 147.7 °C, respectively. Thus, it is a middle ordered melting type of novel series whose total mesophaselength ranges from 20.0°C to 56.0°C. Textures of nematic are threaded or schlieren and that of smectic are smectic A or C.     

Reentrant nematic phase with the new pentamorphism n sa sc nre sare in a mixture

Three homologues of the new series 4 - cyanobenzylidene - 4′ - [4″ - alkoxybenzoyloxy] anilinie are presented. One of them exhibits a reentrant nematic and a reentrant smectic A phases. A diagram of state with 4 - cyanobenzylidene - 4′ - [4″ - decyloxybenzoyloxy] aniline and 4 - [4″ - decyloxybenzoyloxy] benzylidene - 4′ - cyanoaniline has been studies. In the system studies, the following new phase sequence was found with decreasing temperature N S_A S_C N S_A.     

Mesomorphic Properties of an Homologous Series of Alkoxy-Terminated Enamine-Ketone Containing Liquid Crystals

An homologous series of enamine-ketone compounds has been synthesized and their thermal properties investigated. The bis [3- p-n-alkoxyanilino)-2-butenoyl] benzenes exhibited nematic mesophases when the terminal alkoxy substituents were short and both nematic and smectic mesophases when the terminal alkoxy substituents contained twelve or more carbons. The thermal data indicate that although crystalline order is largely determined by the packing of the hydrocarbon tails, there is a low degree of interaction by the tails in the nematic mesophase.     

Phase transition studies in certain thermotropic liquid crystals thermal microscopy and DSC

Investigations on the phase transition studies in the thermotropic liquid crystals, (1) pcyanophenyl trans-4-propylcyclohexane carboxylate, (2) p-cyanophenyl trans-4-pentyl-cyclohexane carboxylate, (3) 4′-n-pentyloxy-4-cyanobiphenyl and (4) 4′-n-octyloxy-4-cyanobiphenyl are carried out by the thermal microscopy and the differential scanning calorimetric (DSC) studies. These studies reveal that the first three mesogens exhibit a single mesophase while the fourth one exhibits a smectic A phase in addition to the nematic phase. The textures exhibited by these mesogens in their mesophases and their transition temperatures, enthalpies and entropies are presented.     

Dependence of liquid crystallinity on molecular rigidity

A novel homologous series of liquid crystals (LC) of chalconyl derivatives is synthesized and studied with a view to understanding and establishing the effects of molecular structure on liquid crystal properties. The novel series consists of 12 homologues. Nematogenic LC property commences from C₃ and continues up to C₁₄ and the smectogenic mesophase is exhibited from C₄ to C₁₆. The C₃ homologue is a monotropic nematic and the rest of the homologues are enantiotropically smectic and nematic or only smectic (C₁₆). Transition curves Cr-Sm, Sm-N, Cr-I, and N-I behave in normal manner with exhibition of odd-even effect, showing phase behaviors of the series.     

Effect of Nitro Terminal Substituent on the Liquid Crystalline Characteristics of Ester Mesogens: p-Nitrophenyl-p'-n-Alkoxycinnamates

The homologous series p-nitrophenyl-p'-n-alkoxycinnamates is a medium melting homologous series; the first two members are non-mesogens and do not exhibit even monotropy. The nematic phase begins from the third derivative in monotropic condition; from the fourth member enantiotropic mesomorphism commences. Polymesomorphism begins from the sixth member with the appearance of smectic mesophase and ends at the seventh member. The rest of the homologues up to the octadecyl are purely smectogens. Thus the homologous series is predominantly smectogenic even though -NO₂ group is reported to be enhancing nematic character.^' Within the polymesomorphic region the nematic mesophase is homeotropic; however, it shows a clear threaded texture where it is the only mesophase shown. The N-I transitions do not exhibit the usual alternation in transitions which is a rare phenomenon. The N-I transition curve is unusually neither rising nor falling though a slight curve is seen; it merges with the S-I curve which shows a slight rising tendency as the alkyl chain length is increased. The S-N transition curve steeply rises and seems to be merging with the S-I curve. The mesomorphic range is good; the nature of the curve can predict the latent N-S or I-N transitions. All smectic orientations are of focal conic smectic A texture except in the case of sixth and seventh homologues where homeotropic nature prevails.     

Mesomorphic Heterocyclic Homologous Series: 1.7-(4'-n-Alkoxybenzoyloxy)-3-acetylcoumarins 11. 4'-Formylphenyl 7-n- alkoxycoumarin-3-carboxylates

Two homologous series of coumarin derivatives have been synthesized and mesomorphic behavior of their members has been studied. In case of Series I, mesomorphism does not begin to appear until the butyl homolog, which is monotropic nematic. The remaining members of the series exhibit both nematic and smectic or only smectic properties. In case of Series II, all the homologs, except the first seven, exhibit only a smectic phase. In both the series, plots of S-N or I transition temperatures versus the number of carbon atoms in the alkoxy chain show an ascending tendency.