Mesogenic cinnamates with a substituted ethyl terminal chain*

Two new mesogenic homologous series of liquid crystalline cinnamates with substituted ethyl tails, β‐methoxyethyl [4‐(4′‐n‐alkoxycinnamoyloxy)benzoates (I) and β‐chloroethyl [4‐(4′‐n‐alkoxycinnamoyloxy)benzoates (II), have been synthesized and characterized by a combination of elemental analysis and standard spectroscopic methods. In series I, lower‐chain members exhibit nematic mesophase, middle members exhibit enantiotropic nematic as well as smectic A (SmA) mesophases, whereas higher members exhibit only an enantiotropic SmA mesophase. In series II, methoxy to n‐butyloxy derivatives exhibit a monotropic nematic mesophase. The SmA mesophase commences from n‐propyloxy derivative as monotropic and persists up to the last member synthesized. The mesomorphic properties of present series were compared with each other and with a structurally related mesogenic homologous series to evaluate the effects of substituted ethyl tail and cinnamoyloxy central linkage on mesomorphism.     

Synthesis of two naphthyl-containing homologous series of mesogenic ligands and the related metallomesogens containing Cu(II)

Two new naphthyl-containing homologous series of mesogenic ligands, the 4-n-alkoxy-2-hydroxybenzylidene-2'-naphthylamines (series I) and 4(4'-n-alkoxybenzoyloxy)-2-hydroxybenzylidene-2'-naphthylamines (series II), as well as the related metallomesogens of higher homologues containing a Cu(II) atom, have been synthesized. All the ligands and complexes were characterized by a combination of elemental analysis and standard spectroscopic methods. In series I, n-heptyloxy and n-octyloxy derivatives are non-mesogenic whereas the remaining higher members synthesized exhibit a monotropic nematic mesophase. In series II, all the members synthesized exhibit an enantiotropic nematic mesophase. All the metallomesogens of series I synthesized exhibit a monotropic smectic A mesophase, except for the n-octyloxy derivative, which is non-mesogenic, whereas metallomesogens of series II exhibit enantiotropic nematic mesophases up to the n-tetradecyloxy derivatives; the n-tetradecyloxy and n-hexadecyloxy derivatives also exhibit smectic C mesophases. All the members of series II and their metallomesogens exhibit mesophases with wide temperature ranges and greater thermal stability as compared to series I and their metallomesogens, respectively. The mesomorphic properties of both the present series and their metallomesogens are compared with each other and with other structurally related series to evaluate the effect of the naphthalene moiety on mesomorphism.     

Azomesogens containing an ethoxyethyl terminal chain: synthesis and characterization

Two homologous mesogenic series, the ethoxyethyl 4-(4'-n-alkoxyphenylazo)benzoates (I) and the ethoxyethyl [4-(4'-n-alkoxybenzoyloxy)phenylazo]-4'-benzoates (II), both containing a terminal ethoxyethyl chain, have been synthesized. In series I, all nine members synthesized exhibit only an enantiotropic smectic A mesophase. In series II, all 12 homologues exhibit an enantiotropic nematic mesophase; a smectic A phase appears in the n-butyloxy derivative as a enantiotropic phase and persists through to the n-hexadecyloxy member. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effects of the ethoxyethyl chain on mesomorphism.     

Synthesis and characterization of two isomeric liquid crystal series with reactive double bonds

Two series of potentially cross-linkable liquid crystal materials derived from p-phenylenebisacrylic (series I, n(P.FB.P), n = 2-10) and p-hydroxycinnamic acid (series II, n(HC.T.HC), n = 2-10) have been synthesized and their thermal and mesomorphic properties studied. All these compounds show enantiotropic mesomorphism over a wide range of temperatures. Compounds with short terminal chains are nematic and when the terminal chain length is increased they show smectic polymorphism-smectic A and C. Most of the compounds are thermally stable over their mesophase ranges.     

Synthesis and characterization of new liquid crystalline materials containing a non-activated arylazoindolinobenzospiropyranyl group as a chiral unit. Part II

Two series of new liquid crystalline compounds containing a non-activated arylazoindolinobenzospiropyran, ABP-SPAB 1a-1e (series 1) and SPAP-ABPC 2a-2e (series 2), have been synthesized. These LC dyes were characterized by a differential scanning calorimetry polarizing optical microscopy, X-ray diffraction and electro-optical measurements. All but one of the series 1 compounds examined exhibit monotropic second and/or third transition liquid crystal phases on cooling from the isotropic liquid. In particular, ABP-SPAB 1b shows a monotropic SmC phase, in addition to a SmA phase. In series 2, most of the compounds exhibit a monotropic nematic phase on cooling. SPAP-ABPC 2c forms an enantiotropic nematic phase and a monotropic SmA phase; 2e shows enantiotropic nematic and SmA phases.     

Azomesogens with polar chloro,nitro and phenolic –OH substituents

Two new mesogenic homologous series containing chloro, nitro and phenolic hydroxy groups were synthesised and their molecular structures characterised by a combination of element analysis and standard spectroscopic methods. The mesomorphic behaviour of the compounds of both series was investigated by polarising optical microscopy and, in some cases, differential scanning calorimetry. All the compounds of both the series exhibit an enantiotropic nematic mesophase. In series I higher members also exhibit an enantiotropic smectic A (SmA) mesophase, whereas in series II the enantiotropic SmA mesophase commences somewhat earlier for the middle members. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effects of different polar substituents on mesomorphism.     

Synthesis,characterisation and liquid crystalline properties of some Schiff base and cinnamate central linkages involving 1,3,5-trisubstituted pyrazolone ring system and their Cu(II) complexes

Two new mesogenic homologous series, each containing 1,3,5-trisubstituted pyrazolone derivatives, 4-n-alkoxyphenyl and Schiff base–cinnamate central linkages, have been synthesised to give 4-[(5-hydroxy-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl) methyleneamino] phenyl 3-(4-n-alkoxyphenyl)acrylate [Series-A] and 4-[(5-hydroxy-3-methyl-1-p-tolyl-4,5-dihydro-1H-pyrazol-4-yl)methyleneamino] phenyl 3-(4-n-alkoxyphenyl)acrylate [Series-B] and their Cu(II) complexes have also been synthesised. These compounds were characterised by elemental analysis, Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (¹H NMR), carbon-13 NMR (¹³C NMR) and ultraviolet (UV)-visible and mass spectral studies. Their mesomorphic behaviour was studied by polarising optical microscope (POM) with a heating stage. POM data were compared with differential scanning calorimetry thermograms. In Series-A and -B, all compounds exhibit mesomorphism. Series-A compounds exhibit an enantiotropic nematic mesophase except propyl derivative, while a smectic A (SmA) mesophase is observed from the heptyl derivative and persists up to the last member of the homologous series. n-Heptyloxy derivative is monotropic for SmA phase. Series-B compounds also exhibit the enantiotropic nematic mesophase, while the SmA mesophase is observed from the heptyl derivative and persists up to the last member of the homologous series. n-Dodecyloxy derivative exhibits monotropic SmA and nematic mesophases. The mesomorphic properties of both series are compared with each other and the other structurally related compounds. The study reveals that cinnamate linkage containing liquid crystals have higher thermal stability compared to structurally related series containing chalcone linkage. In case of complex series, only one compound from each series gives nematic mesophase.     

Mesogenic benzothiazole derivatives with methoxy substituents

Two new mesogenic homologous series containing 6-methoxybenzothiazole ring at the terminus of the molecule, viz. 2-(4′-n-alkoxyphenylazo)-6-methoxybenzothiazoles and 2-[4′-(4″-n-alkoxy-benzoyloxy) phenylazo]-6-methoxybenzothiazoles were synthesized. In series I,n-butyloxy to n-tetradecyloxy derivatives exhibit nematic mesophase. Smectic A mesophase commences from then-dodecyl-oxy derivative as a monotropic phase and is retained up to the last member synthesized. All the members of series II exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related series to evaluate the effect of the benzothiazole ring and the methoxy substituent on mesomorphism. This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore during 9–11 October 2003     

Azo compounds and Schiff 's bases derived from 5-(4-pyridyl)-2-amino-1,3,4-thiadiazole: synthesis, mesomorphic properties and structural study by semi-empirical calculations

The synthesis and liquid crystalline properties of new Schiff 's bases (series 3a-f) and azo compounds (4a-f) incorporating pyridine and 1,3,4-thiadiazole rings are reported. The first homologues in the series of Schiff's bases (3a-c) show a monotropic mesophase and the homologues 3d-f display an enantiotropic SmA phase. The only azo compounds to exhibit liquid crystalline properties are the homologues 4e, f which show a monotropic nematic phase. These series are compared with Schiff's bases and azo compounds analogues (series 5 and 6), previously reported by us and an AM1 study of the structure/mesomorphic property relationship is described.     

Azomesogens with methoxyethyl tail: Synthesis and characterization

Two new mesogenic homologous series are synthesized from methoxyethyl 4-(4′-hydroxyphenylazo) benzoate. In series I the phenolic -OH group is alkylated, whereas in series II it is esterified with 4-n-alkoxybenzoyl group. In series I, all the nine members synthesized exhibit only enantiotropic smectic A mesophase. In series II, all the twelve homologues exhibit enantiotropic nematic mesophase. Smectic A mesophase appears from then-decyloxy derivative as a enantiotropic phase and persists till the last n-hexadecyloxy member. The mesomorphic properties of both the series are compared with each other and also with the properties of other structurally related series to evaluate the effect of the methoxyethyl tail on mesomorphism.     

Mesogenic quinazolone derivatives: synthesis and characterisation

Two new mesogenic homologous series of quinazolone derivatives have been synthesised by condensation of 4-n-alkoxybenzoyloxy benzaldehyde (for series I) / 4-n-alkoxy-3-methoxybenzoyloxy benzaldehyde (for series II) with 3-amino-2-methyl quinazolone in alcohol. The synthesised compounds are characterised by a combination of elemental analysis and standard spectroscopic methods. In series I, all the synthesised members exhibit the nematic mesophase. An enantiotropic smectic A phase is observed from the n-decyloxy derivative onward to the last homologue synthesised. Methoxy to n-propyloxy derivatives of series II are non-mesogenic, whereas the rest of the members exhibit a monotropic nematic mesophase. The mesomorphic properties of the present series I and II are compared with each other and with the other structurally related mesogenic homologous series to evaluate the effect of lateral methoxy substituent and quinazolone moiety on mesomorphism.     

Synthesis and mesomorphic properties of new liquid crystalline compounds VIII. Indolinobenzospiropyranyl aryliminobenzoates

A series of new liquid crystalline compounds, indolinobenzospiropyranyl aryliminobenzoates, 1a-d, have been synthesized and their mesomorphic properties characterized. Analysis by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction showed that the benzoates 1a and 1d form a monotropic mesophase, whereas 1b and 1c show an enantiotropic mesophase. Enantiomorphic properties are uncommon to spiropyran-containing LC molecules. Among the compounds investigated, 1a was found to exhibit a monotropic SmC phase between 90 and 79°C.     

Synthesis and study of 4-(4'-n-alkoxybenzoyloxybenzoyl)-4'-n-butoxyanilides

Thirteen compounds with ester and amide linkages were synthesized and their mesogenic properties evaluated. Methyl to n-propyl derivatives exhibit nematic phases, n-butyl to n-decyl derivatives exhibit smectic and nematic mesophases, whereas n-dodecyl to n-octadecyl derivatives exhibit only smectic phases. All the smectic homologues exhibit smectic C phases. Middle members of the homologous series exhibit polymorphism of smectic mesophase. A plot of transition temperatures versus number of carbon atoms in the alkoxy chain reveals an odd-even effect for nematic-isotropic transition temperatures. Nematic-isotropic and smectic-cholesteric thermal stabilities of the prepared compounds (series I) are higher compared to those of previously reported compounds, series A, B and C. The results indicate that a simple reversal of a central linkage has a dramatic effect on the appearance of smectic mesophase in a homologous series. The structures of the synthesized compounds were characterized using elemental analysis, thin-layer chromatography and spectral data.     

The influence of terminal chlorine on the mesomorphic properties of new thiobenzoates containing two and three benzene rings

New liquid crystalline chloro-substituted thioesters containing two and three benzene rings have been synthesized. 4-Chlorophenyl 4-n-alkoxythiobenzoates and 4-chlorophenyl 4-n-alkoxybenzoyloxy-4'-thiobenzoates are referred to as nO.SCl and nO.OSCl, respectively, where n varies from 4 to 16 for nO.SCl, from 4 to 10 for nO.OSCl and denotes the number of carbon atoms in the alkyl chain. Their mesomorphic properties were investigated by means of polarizing optical microscopy, differential scanning calorimetry, transmittance light intensity and X-ray diffraction measurements. The nO.SCl homologous series possesses smectic A (SmA) and nematic (N) phases for n = 4, 5, 6 while higher homologues have only an enantiotropic SmA phase. Those from the nO.OSCl homologous series have enantiotropic N and SmA phases and higher transition temperatures. The range of the N phase decreases, and of the SmA increases, with the elongation of the alkoxy chain in the nO.OSCl homologous series. The effect on mesomorphic behaviour of terminal alkoxy chain lengthening and replacement by chlorine on the other side of the molecule is discussed.     

Induction of smectic layering in nematic liquid crystals using immiscible components IV. The effect of bulky lateral carboxyl substituents on the thermotropic behaviour of 2,5-bis[4-(n-perfluoroheptyloctyloxy)benzoyloxy]toluene

Bulky lateral carboxylate substituents were introduced at the benzylic position of 2,5-bis[4-(n-perfluoroheptyloctyloxy)benzoyloxy]toluene by esterification of the corresponding benzyl bromide with potassium carboxylates. In spite of the bulky lateral substituents, none of the 2,5-bis[4-(n-perfluoroheptyloctyloxy)benzoyloxy]benzyl carboxylates exhibit a nematic mesophase in addition to, or instead of, the smectic mesophases. All of the crystalline and SmC-SmA transition temperatures and, with the exception of the 9-anthracene carboxylate derivative, all of the isotropization temperatures of the resulting 2,5-bis[4-(n-perfluoroheptyloctyloxy)benzoyloxy]benzyl carboxylates are lower than those of the parent toluene compound. The SmC-SmA transition decreases the most, thereby stabilizing the SmA mesophase. In most cases, the SmC mesophase is destabilized from an enantiotropic to a monotropic mesophase. There is no correlation between any of the transition temperatures and the size of the lateral substituent.     

The preparation and properties of low molar mass liquid crystals possessing lateral alkyl chains

The first twelve members of three new mesogenic homologous series have been characterized, each of which are composed of molecules possessing lateral alkyl chains. The n-alkyl 2,5-bis-(4-n-hexyloxy-benzoyloxy)-benzoates are purely nematic whereas both nematic and smectic behaviour is observed for the 4-cyano-4'-biphenylyl 3'-n-alkyloxybenzoates and the 4-cyano-4'-biphenylyl 3',4'-n-alkyloxybenzoates. The transitional properties of these series are similar to those of the analogous conventional mesogens and hence, can be rationalized without making any special assumptions concerning the conformational distribution of the lateral alkyl chain.     

Synthesis and characterization of new liquid crystalline materials containing a non-activated arylazoindolinobenzospiropyranyl group as a chiral unit. Part II

Two series of new liquid crystalline compounds containing a non-activated arylazoindolinobenzospiropyran, ABP-SPAB 1a-1e (series 1) and SPAP-ABPC 2a-2e (series 2), have been synthesized. These LC dyes were characterized by a differential scanning calorimetry polarizing optical microscopy, X-ray diffraction and electro-optical measurements. All but one of the series 1 compounds examined exhibit monotropic second and/or third transition liquid crystal phases on cooling from the isotropic liquid. In particular, ABP-SPAB 1b shows a monotropic SmC phase, in addition to a SmA phase. In series 2, most of the compounds exhibit a monotropic nematic phase on cooling. SPAP-ABPC 2c forms an enantiotropic nematic phase and a monotropic SmA phase; 2e shows enantiotropic nematic and SmA phases.     

Synthesis and transition temperatures of novel fluorinated chiral liquid crystals containing 1,4-tetrafluorophenylene units

To continue the search for novel series of fluorinated ferroelectric liquid crystals, an additional two series of 4-[(S)-2-methylbutoxy]phenyl 4-[(4-n-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl] benzoates (C) and 4-(n-alkoxy)phenyl 4-[(4-(S)-2'-methylbutoxy-2,3,5,6-tetrafluorophenyl)] benzoates (D) have been synthesized. Polarizing microscopic textural observations and DSC measurements of the phase transitions of these novel compounds showed that compounds C were liquid crystals with a chiral nematic (N) phase and a monotropic chiral smectic C phase (S_c), and compounds D exhibited a chiral nematic (N) phase.     

Cholesterol-based dimeric liquid crystals: synthesis and mesomorphic behaviour

Chiral non-symmetric dimeric liquid crystals consisting of a cholesteryl ester moiety as chiral entity and a biphenyl aromatic core, interconnected through n-butyl (C₄) or n-pentyl (C₅) parity alkylene spacers, have been synthesized and investigated for their liquid crystalline properties. All the dimers exhibit enantiotropic mesophases. The first member of the dimers having the C₄ central spacer exhibit only the chiral nematic (N*) mesophase, while the higher homologues also show smectic A (SmA) and twist grain boundary (TGB) mesophases. The dimers of the other series containing the C₅ central spacer also have stable SmA, TGB and N* mesophases, except for the first which does not show the TGB phase. Both series of compounds show a weak odd-even effect with terminal alkyl chain substitution, while the spacer length has a marked influence on the phase transition temperatures.     

Liquid crystalline behaviour from binary mixtures of non-mesogenic 4-alkyl-N-(4-cyanophenyl) piperidines [1]

A relatively rare phenomenon, the induction of thermotropic mesophases from combinations of homologues of non-mesogenic compounds, is examined in some detail. Thus, monotropic nematic phases have been obtained from binary mixtures of 4-alkyl-N-(4-cyanophenyl)piperidines (I). Except for the hexyl homologue, the compounds I with butyl to nonyl as alkyl groups are non-mesomorphic as neat materials. From phase diagrams, the nematic clearing temperatures of the binary mixtures are found to vary linearly with composition and to increase as the molecular lengths of the components are increased. By introducing a methyl group at the 1-position of the alkyl chain, the melting points of the neat components are depressed, and the nematic clearing temperatures of the binary mixtures are lowered. Factors associated with the induction of this mesomorphism and with the 'kinetic' and thermodynamic stabilities of the monotropic nematic phases are discussed. Among these is the orientation between the rings of the core groups in I and in the more common mesogens, the trans-4-alkyl-1-(4-cyanophenyl) cyclohexanes, II.