Mesomorphism dependence on molecular rigidity and flexibility

A novel homologous series of mesogens was synthesized and studied with a view to understanding and establishing the relations between molecular structure and liquid crystal properties. Eleven members of the series were synthesized. Mesogenic behavior commences from the C₆ member and continues up to the C₁₄ member. The rest of the members, C₁ to C₅ and C₁₆, are non-mesogenic. Mesogenic homologues (C₆ to C₁₄) are enantiotropically nematogenic. Textures of nematic phase are threaded or Schlieren. Transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. Analytical and structural data confirm the molecular structures of homologues. Thermal stability for nematic phase is 198.0°C. Mesomorphic phase length ranges from 11.0°C to 50.0°C. Cr-I/N and N-I transition curves of a phase diagram behave in normal manner from C₁ to C₁₂ members, and higher members C₁₄ and C₁₆ deviated from normal behavior. Mesogenic properties of present novel ester series are compared with the structurally similar series. Odd-even effect is missing for the N-I transition curve. Thus, the present series is partly nematogenic without exhibition of smectic property whose transition temperatures vary between 153°C and 210°C.     

Study of deviation from normal liquid crystal behavior of mesomorphic-isotropic transition curve in a chalconyl ester series with equipolar terminal end groups

A novel chalconyl ester homologous series RO.C₆H₄.COO.C₆H₄.CO-CH:CH-C₆H₄.OC₈H₁₇(p) synthesized and studied with a view to understanding and establishing the relation between molecular structure and Liquid Crystal (LC) properties of thermotropic mesomorphs. The novel series consists of eleven homologous (C₁ to C₁₆). Enantiotropicnematic type of mesophase formation commences from C₃ homologue and continued up to the last C₁₆ homologue of a novel series. Smectogenic character is totally absent for the novel series. Transition temperatures and the textures of nematic phase were determined through an optical polarizing microscopy (POM) equipped with a heating stage. Textures of nematic phase are threaded or Schlieren. Transition curve Cr-N/I and N-I behaved in normal manner except C₈ homologue which showed negligible deviation from normal behavior. N-I transition curve exhibited odd–even effect. Analytical and structural data supported the molecular structures of homologues. Average thermal stability for nematic is 98.88°C whose degree of mesomorphismvary from 12.0°C to 37.0°C. Evaluated thermometric data of present novel series are compared with structurally similar series. Group efficiency order for nematic on the basis of thermal stability, early commencement of mesophase and the degree of mesomorphism. Thus, present series is predominantly nematogenic and lower middle ordered melting type the low degree of mesomorphism.     

Dependence of mesomorphism on geometrical shapes of isomeric and nonisomeric series of chalconyl esters

A meta substituted chalconyl ester homologous series: RO?C₆H₄?COO?C₆H₄(meta)?CO?CH?CH?C₆H₄?OC₁₂H_25(n)(para) is synthesized and studied with a view to understanding the effect of molecular substitution at meta position in a molecular structure on thermotropic liquid crystal properties. The novel homologous series consists of thirteen homologues (C₁ to C₁₈). All the homologues except the nonliquid crystal homologues C₁, C₂, C₃ are enantiotropic nematic with the absence of smectic properties. The transition and melting temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren. Transition curves (Cr-N/I and N-I) behave in normal manner except homologues between C₁₀ and C₁₄ of N-I curve, which show negligible deviation from normal and a smooth descending tendency. The N-I transition curve exhibits an odd-even effect up to C₁₀ homologue and then the odd-even effect disappears for higher homologues. Analytical and the spectral data support the molecular structures. Thermal stability for nematic is 107.3°C and the mesophase lengths range between 13.0°C and 35.0°C at the C₁₈ and C₁₂ homologues respectively. Group efficiency order for nematic is derived on the basis of thermal stability as ?OC₁₂H_25(n) (linear) > ?OC₁₂H_25(n) (nonlinear) > ?OC₁₆H₃₃ (nonlinear).     

The Liquid Crystal Properties of Some Aromatic Esters Derived From Naphthalene

Abstract The 2,6-naphthylene ring system has been used to replace each of the 1,4-phenylene rings in various 4-substituted-phenyl 4-substituted-benzoates, where the substituents were alkyl and/or alkoxy. For the dialkyl esters, the N-I temperatures were increased by 60–80° compared with the simpler, analogous phenyl benzoates, irrespective of the position of the 2,6-naphthylene ring. For the esters with one alkyl and one alkoxy substituent, the N-I temperatures were again higher than those of the corresponding phenyl benzoates (～60°); S_A properties were quite pronounced in the 6-alkyl-2-naphthyl 4-alkoxybenzoates. When both substituents were alkoxy groups, S_C phases of quite wide thermal range were exhibited, usually preceded on cooling by a nematic and a S_A phase.     

Mesomorphism dependence on lateral substitution of functional groups and their position in series: 4(4′-n-alkoxy benzoyloxy)-3-chloro phenyl azo-2″-methoxy benzenes

Eleven homologues of the title series were synthesized. The methyl-to-pentyl derivatives are nonmesomorphic. The nematic mesophase commences from the sixth member of the series without any smectic phase. An odd–even effect in the nematic–isotropic transition curve is not observed. The nematic mesophase appeared as a threaded or a Schlieren-type texture as observed through a hot-stage polarizing microscope. The nematic–isotropic transition temperatures are between 89°C and 127°C with the mesomorphic range varying from 9°C to 44°C at the hexyl and tetradecyl derivative of the series, respectively. The nematic–isotropic transition curve initially rises and then falls in a normal manner as the series is ascended, but it abnormally rises beyond the 10th homologue. The series is enantiotropic nematic with a middle-ordered melting type. Analytical data support the structures of the molecules. The thermal stability and some other mesomorphic characteristics are compared with structurally similar homologous series. The average nematic–isotropic thermal stability is 105.4°C.     

Synthesis,Thermodynamic Properties,and Gas- Liquid Chromatographic Evaluation of a High-Melting Liquid Crystal Series

The synthesis, phase transition temperatures and thermodynamic data (enthalpies and entropies) are reported for the methoxy through n-octyloxy (and n-decyloxy) homologues of the liquid crystal series represented by N,N′-bis[p-alkoxybenylidene]-α, aα′-bi-p-toluidine. The trends in transition temperatures are more or less analogous to previously-studied liquid crystal series. Nematic-isotropic enthalpy values are appreciably higher than average values for other series. Entropy values show the usual odd-even effect, but in contrast to observed trend for other series, they decrease with increasing terminal substituent chain length. Di-Schiff' s bases with various terminal substituents that showed interesting linear correlation between nematicisotropic transition temperatures and the anisotropy of polarizability of the substituent were also synthesized. A simple gas-liquid chromatographic method for the investigation of the selectivity of nematic stationary phases and its dependence on the degree of molecular order in the nematic state is also presented.     

Study of mesomorphism and laterally substituted nitro group

A novel thermotropically mesomorphic, meta-substituted nitro group of chalconyl ester series, RO-C₆H₄-COO-C₆H₃-(NO₂)-CO-CH=CH-C₆H₄OC₁₂H₂₅(n) (para) is synthesized and studied with an aim to establish the relation between molecular structure and the mesomorphism with reference to changing molecular flexibility in presence of nitro lateral group. Novel homologous series consist of thirteen homologs (C₁–C₁₈) whose mesomorphism commences from C₅ homolog as enantiotropic nematogenic with absence of smectic property, even in the monotropic condition. Transition temperatures of novel substances were determined by an optical polarizing microscope, equipped with a heating stage (POM). Textures of a nematic phase are threaded or Schlieren. N-I transition curve exhibited narrow, sharp and short odd-even effect; with deviating trend in a phase diagram. Analytical, spectral and thermal data confirmed the molecular structures of homologs. Thermal stability for nematic is 182.89°C, whose mesophase lengths minimum to maximum ranges from 17°C to 45°C and it is an upper middle ordered melting type series. Group efficiency order for nematic is series 1 > series Y > series X, as derived from comparative study of structurally similar analogous series.     

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.     

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.     

Study of mesomorphism dependence on molecular flexibility of an azoester series containing a napthyl unit

A novel azoester homologous series of liquid crystalline (LC) compounds: RO?C₆H₄-COO?C₁₀H₆-N:N-C₆H₄?OC₄H₉(n) without lateral substitution has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on thermotropic LC substances with reference to tailed-end group. The novel homologous series consists of 13 homologs (C₁ to C₁₈) whose nematogenic and smectogenic mesomorphism commences enantiotropically from C₆ and C₁₂ members of the series, respectively. The C₁₂–C₁₈ homologs are smectogenic and C₆–C₁₈ are nematogenic, of which C₁₂–C₁₈ homologs are smectogenic plus nematogenic. The C₁–C₅ homologs are nonmesogenic. Transition temperatures and the textures of the homologs were determined and identified by an optical polarizing microscope (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren and that of the smectic phase are of the type A or C. Transition curves Cr-M/I, Sm-N and N-I of a phase diagram behaved in normal manner except N-I transition temperature of C₁₀ homolog which deviated by 9°C–10°C from normal behavior. N-I transition curve exhibited odd-even effect. Analytical, spectral, and thermal data confirms the molecular structures of homologs. Thermal stability for smectic and nematic are 115.5°C and 138.5°C, respectively whose corresponding mesophaselengths are varied from 10.0°C to 16.0°C and 13.0°C to 24.0°C, respectively. Group efficiency order for smectic and nematic are derived from comparative study of structurally similar analogous series; as smectic: ?OC₄H₉ (n) > ?CH₃ > ?H; Nematic: ?H > ?OC₄H₉ (n) > ?CH₃     

Synthesis of novel ester series and study of its mesomorphism dependence on terminal end group with lateral –OCH3 group

Novel liquid crystal (LC) materials of ester derivatives were synthesized and studied with a view to understanding and establishing the effects of molecular structure on LC properties. The novel molecules consist of two phenyl rings bonded through –COO– central group and a laterally substituted methoxy group with –OC_nH_2n+1 as well as –COOCH₃ terminal end groups, and yielded 12 homologous members of an ester series. The C₁ to C₃ members are nonmesomorphic, the C₄ to C₁₂ members are enantiotropic nematic only, and the C₁₄ to C₁₆ members are enantiotropically smectogenic in addition to nematogenic. Transition temperatures and the textures of LC state were observed through an optical polarizing microscope (POM) equipped with a heating stage. The textures of nematic phase are threaded or Schlieren, and that of smectic phase are focal conic of the type A or C. Transition curves of a phase diagram behave in normal manner with the exhibition of an odd-even effect (only N-I). Analytical and spectral data support the molecular structures of the novel ester derivatives. The LC properties of the present series are compared with structurally similar other known series. The average thermal stability of the series is 93°C for smectic and 120.88°C for nematic and the mesogenic phase length ranges between 2°C and 46°C.     

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 on molecular rigidity

A novel ester homologous series of thermotropic liquid crystal (LC) has been studied with a view to understanding and establishing the relation between LC property and the molecular structure. The series consists of 11 members, the C₁–C₅ and C₁₆ members of the series are nonliquid crystals. LC properties commence from the C₆ homolog and continue up to the C₁₄ homolog as enantiotropic nematic and smectic in addition to nematic. Transition temperatures of the homologs were determined by an optical polarizing microscope equipped with a heating stage. Textures of nematic phase are threaded or Schlieren and that of smectic is focal conic of the type-A. Analytical and spectral data confirm the structures of homologs. Thermal stability for nematic is 93 °C and 136 °C, respectively. The N–I and Sm–N transition curves of phase diagram do not exhibit odd-even effect. The N–I transition curve partly behaves in an abnormal manner. The Cr–I and Sm–N transition curves behave in normal manner. The LC behavior of the present series is compared with structurally similar known homologous series.     

Study of the Effect of Lateral Substitution on Mesogenic Behavior with Reference to -CH=CH- Unit

A novel cinnamate ester homologous series has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on liquid crystal (LC) properties with a focus on the highly polar methoxy group as a lateral substituent. The series consists of twelve homologs; of which C₁–C₅ are nonmesogenic, and the rest of the homologs are enantiotropically smectogenic or and nematogenic. The texture of nematic phases is threaded or Schlieren and that of the smectic is either smectic A or C, as recognized and determined through an optical polarizing microscope equipped with a heating stage. The Sm-N I and N-I transition curves exhibit odd-even effects and behave in normal manner. The Cr-I M behaves in normal manner. Analytical and spectral data confirm the molecular structures of homologs. The average thermal stabilities for smectic and nematic are 125.3 C and 129.8 C, respectively, whose total mesophase length varies from 13 C to 51 C. Some LC properties of present series are compared with the structurally similar known series.     

Molecular structural flexibility dependence of mesomorphism through ortho-substituted bromo group

A novel series of liquid crystal (LC) materials of Schiff's bases viz. RO-C₆H₄?CH?CH?COO?C₆H₄?N?CH?C₆H₄?Br (ortho) is synthesized and studied with a views to understanding and establishing the effect of molecular structure on liquid crystal properties and to provide novel thermotropic LC material to the scientific and technological community of research interest. The novel series consists of thirteen members (C₁ to C₈, C₁₀, C₁₂, C₁₄, C₁₆ &; C₁₈). All the members of a series are enantiotropic liquid crystals. Smectic (C₁₀?C₁₈) and nematic (C₁?C₁₈) property commence from C₁₀ and C₁ homologue respectively. Transition temperatures and the textures of homologues were determined using a polarizing optical microscope (POM) equipped with a heating stage. Transition curves Cr-M, Sm-N and N-I of a phase diagram behaved in normal manner. Odd–even effect is absent for Sm-N transition curve, but it is present for N-I curve. Sm-N transition curve is extrapolated to C₈ and C₆ nonsmectogenic homologues to determine and predict their latent ability for exhibition of smectic property. Analytical and spectral data confirms the molecular structures of homologues. Thermal stabilities of smectic and nematic are 85.4°C and 130.1°C °C whose upper and lower total mesophase length vary from 58.0°C to 06.0°C at the C₁₀ and C₁ = C₅ = C₆ homologue, respectively. Textures of nematic phase are threaded or Schlieren and smectic phase are of type A or C. LC properties of present novel series are compared with structurally series known series. Thus, present novel series is predominantly nematogenic and partly smectogenic with middle ordered melting type and considerable total mesophase length range.     

Synthesis and some Physical Properties of 1-Cyclohexyl-2-(4”-Halobiphenyl-4'-yl)Ethanes

A series of 1-(trans-4'-n-alkylcyclohexyl)-2-(4”-halobiphenyl-4'-yl)ethanes, which show nematic phases, was prepared. Their transition temperatures, enthalpies and entropies were measured. Their bulk viscosities, birefringences and dielectric constants were determined by extrapolation. 1-(trans-4'-n-propylcyclohexyl)-2-(4”-fluorobiphenyl-4'-yl)ethane has a high clearing of 125° C, a low viscosity of 25 c.p. at 20 °C, a relatively high birefringence of 0.166 at 25 °C, and a positive dielectric anisotropy of 4.9. The transition temperatures, the N-I transition entropies, the bulk viscosities and the birefringences for the 1-(trans-4'-n-alkylcyclohexyl)-2-(4”-fluorobiphenyl-4'-yl)ethanes exhibited odd-even effects in relation to the number of carbon atoms in the alkyl chain. The bulk viscosity as a function of the third power of the van der Waals radius of the halogeno group, the birefringence as a function of the van der Waals radius of the halogeno group, and the dielectric constants as a function of the dipole moment of the halogeno group are discussed for the 1-(trans-4'-n-propylcyclohexyl)-2-(4”-halobiphenyl-4'-yl)ethanes.     

Mesomorphism dependence on halogenated chalconyl esters in terms of molecular flexibility/rigidity

Vinyl carboxy central group containing a novel chalconyl ester homologous series: RO.C₆H₄.CH ? CH.COO.C₆H₄.CH ? CH.CO.C₆H₄.I (para) have been synthesized and studied with a view to understand and establish the relation between thermotropic liquid crystalline (LC) behaviors and the molecular structure. Novel chalconyl ester homologous series consists of thirteen homologs (C₁–C₁₈). C₁–C₃ homologs are nonmesogenic, C₄ homolog is enantiotropic nematogenic and the rest of the homologs (C₅–C₁₈) are enantiotropically smectogenic plus nematogenic. Phase transition temperatures and textures of LC phase were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Cr-M/I, Sm-N, N-I transition curves in a phase diagram behaved in normal manner. Sm-N and N-I transition curves exhibited odd-even effect from C₄–C₁₀ or nearby C₁₀ homolog. Textures of nematic phase are threaded or Schlieren and that of the smectic phase are of the type smectic A or C. Analytical and spectral data confirms the molecular structure of homologs. Thermal stabilities for smectic and nematic mesophases are 155.0 and 180.7, respectively, and their corresponding mesophaselengths are varied from minimum to maximum at 17.0°C–39.0°C as well as 15.0°C–30.0°C. Thus, it is middle ordered melting type series. The group efficiency orders derived on the basis of smectic and nematic thermal stabilities are as under: Sm: -C₆H₄.I > -C₆H₄.Cl > -C₄H₃S and N:- C₆H₄.I > -C₆H₄.Cl > -C₄H₃S from comparative study of structurally similar analogous series     

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.     

Synthesis of novel azoester homologous series of liquid crystalline behavior and the study of mesomorphism dependence on lateral substitution of middle phenyl ring

The titled azoester liquid crystalline homologous series consists of eleven homologues. The pentyl to tetradecyl derivatives of the series are nematogenic without exhibition of smectogenic character. Rest of the members of the series are nonliquid crystalline in nature. Textures of the nematic mesophase are schlieren or threaded type. Transition curves in the phase diagram showed normal phase behavior. Transition temperatures and liquid crystal behavior observed under an optical polarizing microscope equipped with a heating stage. An odd even effect is observed for nematic-isotropic transition curve. Analytical and spectral data confirms the structures of the molecules. Present homologous series is predominant nematogenic and partly nonmesogenic. Average thermal stability for nematic is 125.33°C and nematogenic mesophase length varies between 12°C to 48°C at tetradecyl (C₁₄) and octyl (C₈) derivatives, respectively.