Monotropic Mesophase Research Articles

STUDY ON PHASE TRANSITION FEATURES AND INFRARED SPECTROSCOPY OF 3OCB LIQUID CRYSTAL

In the study, some physical properties of the 3OCB liquid crystal belonging to the cyanobiphenyl group, which is frequently used in dimeric molecules and eutectic mixtures, were investigated. In this context, its optical properties in different temperature interval have been investigated. As a result of optical measurements, it was determined that 3OCB exhibited a monotropic mesophase and that the phase range of the mesophase was determined. In addition, it was observed that a heterophase region appeared in the liquid crystalline isotropic phase-nematic mesophase transition. Morphological analysis of the mesophase and heterophase region was also performed. Also, by performing calorimetric measurements, how the relevant liquid crystal phase interval changes in bulk state was compared with the results obtained from optical measurements. Information about the 3OCB's dominant vibration bands was obtained by performing infrared spectroscopic measurements. The infrared spectroscopy of 3OCB, which is frequently used in industry and scientific studies, has been performed to provide information about the functional groups and structure of the molecule.

Nematic Triphenyltriazine Triesters and the Induction of the Columnar Mesophase by Fluorine Substitution

Whereas their para homologs are not mesogenic, the disk-shaped triphenyltriazine meta-trialkylesters obtained via trimerization of 3-cyanobenzoic alkylester, which are configurationally more flexible, exhibit a monotropic nematic mesophase. Introduction of fluorine atoms into the alkyl chains or into the phenyl moieties leads to the appearance of an enantiotropic columnar mesophase. If fluorine is introduced both in the chains and in the phenyl moieties, only a monotropic mesophase remains. Fluorination of either the alkyl chains or the aromatic core, but not both, appears thus as a simple means of inducing or stabilizing columnar self-assembly in disk-shaped systems. As the homeotropically alignable columnar mesophase can thus be made to persist at room temperature, as energies higher than 3 eV of the first excited triplet state are computed in agreement with the value reported for the parent arene, and as they are not fluorescent themselves, these compounds are of promise as aligning host matrices for blue-emitting TADF devices with improved light outcoupling. Dilution of a columnar with a nonmesogenic homolog induces the nematic state, indicating that the nanoscopic make-up of both mesophases is closely related.

Phase behaviors of classic liquid crystal dimers and trimers: Alternate induction of smectic and twist-bend nematic phases depending on spacer parity for liquid crystal trimers

A new heliconical mesophase without apparent molecular positional ordering, which was discovered in achiral bent molecules [i.e., the twist-bend nematic (NTB) phase], has become a hot topic of research in the field of liquid crystals (LCs). In this study, a series of classic LC trimer homologs, namely 4,4′-bis[ω-(4-cyanobiphenyl-4′-yloxy)alkoxy]biphenyls (CBOnOBOnOCB; n = 4–11), was synthesized, and their phase transitions and mesophase structures were evaluated in detail, to reinvestigate their elusive monotropic mesophases. Polarized optical microscopy (POM) observations revealed that below the nematic (N) phases, even-n homologs exhibited the fan-shaped and polygonal textures of the layered smectic (Sm) phase, while odd-n homologs displayed the blocky and striped textures associated with the recently discovered heliconical NTB phase. X-ray diffraction analyses of CBOnOBOnOCB (n = 10 and 11) revealed that their mesophases exhibited the cybotactic N phase property, and suggested that the monotropic mesophase observed for odd CBO11OBO11OCB was the pseudo-layered heliconical NTB phase rather than the layered Sm phase. Therefore, it was suggested that the Sm and NTB phases were alternately induced, depending on the spacer parity of classic LC trimer homologs CBOnOBOnOCB. This could be ascribed to the steric interactions associated with different molecular geometries, which are largely governed by the imposed spacer parity, and possess parallelly and obliquely located mesogenic biphenyl moieties for the even-n and odd-n homologs, respectively. In addition, the phase-transition behavior of a homologous series of ether-linked cyanobiphenyl-based LC dimers (CBOnOCB; n = 3–12) was investigated. POM observations shows that odd-n CBOnOCB homologs (n = 5, 7, 9, and 11) exhibited the monotropic N–NTB phase transition, which was only observed in the small supercooled N domains. Even-n CBOnOCB homologs exhibited only the N phase and did not exhibit Sm phases below the temperature of the N phase upon cooling. Hence, alternate induction of the Sm and NTB phases depending on n parity was observed only in the LC trimer homologs.

When hydrogen bond tailors molecular packing in non-anisometric molecules. The case study of N-alkyl 1,3-diphenyl-4,5-dihydro-1H-pyrazole-5-carboximidamides

ABSTRACT In this paper, we report the synthesis of novel liquid crystals (LCs) based on 5-membered pyrazoline heterocycle. The synthesis of pyrazoline derivative was carried out by [3 + 2] 1,3-dipolar cycloaddition reaction of benzaldehyde phenyl hydrazone (1) with acrylonitrile, mediated by chloramine-T as the oxidising agent, followed by addition of hydroxylamine hydrochloride, and subsequently alkylated with various alkyl chains to afforded the title compounds. The LCs properties were investigated using differential scanning calorimetry and polarising optical microscopy. For title compounds with longer alkyl chains, monotropic columnar hexagonal mesophase was characterised by XRD analysis. The mesophase-formation was driven by intermolecular hydrogen bonds despite their non-discoid molecular structure.

Mesomorphic properties of liquid crystalline compounds with chalconyl central linkage in two phenyl rings

ABSTRACTIn order to investigate the influence of the central linking group and the effect of flexibility on mesomorphism, we have synthesised a newly homologous series 3-(3-butoxyphenyl)-1-(4-n-alkoxy phenyl) prop-2-en-1-one (series-l) consisting of 13 homologues C1–C8, C10, C12, C14, C16 and C18. In the present series, mesophase commences from the C6 homologue. C1–C5 homologues did not exhibit liquid crystalline (LC) property, while C6–C12 homologues exhibited an enantiotropic nematic phase and the rest of the homologues C14–C18 displayed monotropic SmC and nematic mesophase. The transition temperatures of the synthesised compounds were determined by an optical polarising microscopy equipped with a heating stage. All newly synthesised compounds were confirmed by 1H-NMR, 13C-NMR, IR and elemental analysis.

Mesogenic naphthyl derivatives

ABSTRACTTwo new mesogenic homologous series of liquid crystalline naphthalene derivatives with different central linkages: 2- Naphthyl-4-n-alkoxybenzoates (I) and trans-2-Naphthyl -4-n –alkoxycinnamates(II), have been synthesized and characterized by a combination of elemental analysis and standard spectroscopic methods. Twelve compounds have been synthesized in both the series I and II. In series I, methoxy to n-pentyloxy derivatives are non mesogenic, n-hexyloxy to n-hexadecyloxy derivatives exhibit monotropic nematic mesophase. Smectic A mesophase commences from n-decyloxy derivatives as a monotropy and persist up to the last member synthesized. All the 12 compounds of series II exhibit mesomorphism. Methoxy to n-propyloxy derivatives exhibit monotropic nematic mesophse, and n-butyloxy to n-tetradecyloxy derivatives exhibit enantiotropic nematic mesophase. n-Hexayloxy to n-hexadecyloxy derivatives also exhibit enantiotropic smectic A mesophase. The mesomorphic properties of present series were compared with each other and with a structurally related mesogenic homologous series to evaluate the effects of central linkage on mesomorphism.

Physical properties of 8OS5 thioester studied by complementary methods

ABSTRACTProperties of 4-n-pentylphenyl-4’-n-octyloxythiobenzoate (8OS5), belonging to the nOS5 homologous series, have been studied by complementary methods. The phase sequence, the phase transition temperatures, the thickness of molecular layers, the average distance between long axes of molecules and the correlation length were determined during cooling and heating. For the first time, simultaneous X-ray diffraction and differential scanning calorimetry measurements have been used to study mesomorphic properties. The results are compared with the ones obtained in standard measurements by means of differential scanning calorimetry, X-ray diffraction and polarizing optical microscopy. Meaning of experimental procedures applied in investigations of monotropic mesophases below a melting point is discussed.

Extended conjugated mesogens: synthesis and mesomorphic properties of H-shaped mesogens based on 3,3ʹ,5,5ʹ-tetrasubstituted 2,2ʹ-bithiophene with oligo(1,4-phenyleneethynylene) arms

ABSTRACTA new class of extended conjugated mesogens, namely H-shaped mesogens based on 3,3ʹ,5,5ʹ-tetrasubstituted 2,2ʹ-bithiophene with oligo(1,4-phenyleneethynylene) arms, have been synthesised, and the relationships between molecular structures and mesomorphic properties investigated. Tetraalkyl, tetraalkoxy and dialkyldialkoxy derivatives, [R1C6H4CCC6H2(C2H5)2CC]2[R2C6H4CCC6H2(C2H5)2CC]2C8H2S2 where R1 and R2 = alkyl and alkoxy chains of different lengths, exhibit nematic phases. The length, number and position of the terminal chains strongly affect the mesomorphic properties. The tetraalkyl derivatives in which R1 = R2 = pentyl to heptyl exhibit enantiotropic mesophases, whereas the derivatives with octyl or nonyl chains exhibit monotropic mesophases. The tetraalkoxy derivatives in which R1 = R2 = pentyloxy to nonyloxy all exhibit enantiotropic nematic phases. The mesophase range increases with increasing alkoxy chain length, except that the octyloxy and nonyloxy derivatives have almost the same temperature range. The dialkyldialkoxy derivatives in which R1 = alkyl; R2 = alkoxy and in which R1 = alkoxy; R2 = alkyl (R1 and R2 = heptyl, nonyl, hexyloxy or nonyloxy) exhibit enantiotropic mesophases. The derivatives in which R1 = alkoxy have a significantly lower crystal–nematic transition temperature than the corresponding derivatives (R2 = alkoxy), although the two types of derivatives have a similar nematic–isotropic transition temperature.

Columnar liquid-crystalline dinaphthoperylenetetracarboxdiimides.

Although the double Friedel-Crafts acylation of arenes with ethyl chloroglyoxylate is hindered by the strongly deactivating effect of the first-entering glyoxylic substituent, the double reaction is successful with the reactive arene perylene under long reaction times and with concomitant ester hydrolysis. The reaction is regiospecific, giving the 3,9-regioisomer exclusively. This perylenylenediglyoxylic acid is condensed first with o-bromophenylacetic acid and then with α-branched alkylamines to yield the title compounds. Whilst the corresponding tetraalkyl esters only show monotropic mesophases, these diimides show enantiotropic columnar mesophases that can be maintained at room temperature if racemically branched alkyl chains of moderate size are used. A palladium-induced C-C bond migration during the build-up of the arene system leads to an isomeric side product of reduced symmetry that can be isolated by aggregation-controlled chromatographic separation. The HOMO and LUMO energies of the title compounds are considerably higher than those of established perylenetetracarboxdiimides.

Study of Mesomorphism Through a Novel Homologous Series and Its Relation to Molecular Structure

A novel homologous series 4-(4′-n-alkoxy benzoyloxy)-3-chloro phenyl azo,3″,4″-dichlorobenzenes was synthesized with a view to understand and establish the relation between mesomorphism and the molecular structure. The novel series consists of 12 members, which showed commencement of monotropic nematic mesophase formation from the butoxy homologue and continued up to the hexadecyloxy homologue without exhibition of a smectic mesophase. The textures of the nematic mesophase are threaded or Schlieren in type. Transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. Isotropic-nematic transition curve of the phase diagram behaved in normal manner with exhibition of odd-even effect. Solid-isotropic transition curve behaved descending tendency by adopting zigzag path up to the pentyloxy homologue; which include methoxy to propoxy homologues as nonmesomorphic derivatives. Thermal stability for the nematic is just a few degrees (1°C to 2°C). Analytical and spectral data support the molecular structures. The mesomorphic properties of present novel series are compared with structurally similar other known homologous series.

Dielectric, calorimetric and mesophase properties of 1′′-(2′,4-difluorobiphenyl-4′-yloxy)-9′′-(4-cyanobiphenyl-4′-yloxy) nonane: an odd liquid crystal dimer with a monotropic mesophase having the characteristics of a twist-bend nematic phase

This paper reports a novel liquid crystal phase having the characteristics of a twist-bend nematic phase formed by a non-symmetric ether-linked liquid crystal dimer. The dimer 1''-(2',4-difluorobiphenyl-4'-yloxy)-9''-(4-cyanobiphenyl-4'-yloxy) nonane (FFO9OCB) exhibits two liquid-crystalline phases on cooling at a sufficiently high rate from the isotropic phase. The high temperature mesophase has been reported in the literature as nematic and confirmed in this study. The other mesophase is metastable and can be supercooled giving rise to a glassy state. Its identification and characterization are based on optical textures, broadband dielectric spectroscopy, calorimetry, measurements of both splay and bend elastic constants in the nematic phase and miscibility studies. It is concluded that the low temperature mesophase exhibits the characteristics of a twist-bend nematic phase. Dielectric measurements enable us to obtain the static permittivity and information about the molecular dynamics in the isotropic phase, in the nematic mesophase and across the isotropic-to-nematic phase transition. Two orientations, parallel and perpendicular to the director, have been investigated. In the high temperature nematic mesophase, the dielectric anisotropy is found to be positive. Measurements of the parallel component of the dielectric permittivity are well-explained by the molecular theory of dielectric relaxation in nematic dimers (M. Stocchero, A. Ferrarini, G. J. Moro, D. A. Dunmur and G. R. Luckhurst, J. Chem. Phys., 2004, 121, 8079). The dimer is modelled as a mixture of cis and trans conformers and the model allows an estimate of their relative populations at each temperature. The nematic-to-isotropic phase transition has been exhaustively studied from the accurate evolution of the heat capacity and the static dielectric permittivity data. It has been concluded that the transition is first order in nature, but close to tricritical. The nature of the nematic-to-the novel liquid crystal phase transition is difficult to analyze to the same extent because of insufficient precision. Only observations at cooling rates of 10 K min(-1) or higher were possible because on heating from the glassy state, the twist-bend nematic mesophase crystallizes at temperatures far below the nematic-nematic phase transition.

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.

Macrocyclic Effects in the Mesomorphic Properties of Liquid‐Crystalline Pillar[5]‐ and Pillar[6]arenes

AbstractWhereas the reaction of 1,4‐bis(2‐bromoethyloxy)benzene (4) with paraformaldehyde in the presence of BF3·Et2O afforded exclusively the cyclopentameric pillar[5]arene derivative (5), both cyclopenta‐ and cyclohexameric macrocycles 5 and 6 were obtained when the reaction of 4 with paraformaldehyde was performed at 45 °C in CHCl3 with FeCl3 as the catalyst. Treatment of compounds 4–6 with sodium azide provided the corresponding polyazides, to which a cyanobiphenyl building block was subsequently grafted to generate model compound 1, pillar[5]arene 2, and pillar[6]arene 3, bearing two, ten and twelve mesomorphic subunits, respectively. The liquid‐crystalline and thermal properties of the compounds were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Comparison of the liquid‐crystalline properties of macrocycles 2 and 3 with those of 1 revealed the strong influence of the macrocyclic pillar[n]arene core on the mesomorphic properties. Whereas only a monotropic mesophase was observed for 1, a broad enantiotropic mesophase was evidenced for both pillar[n]arene derivatives.

Mesogens Based on Cholesterol Derivatives: Synthesis and Characterization

A new series of liquid crystals involving cholesterol based mesogenic units and Schiff base moiety interlinked through ester linkage were designed and synthesized. The target compounds were obtained by the reaction of 4′-(3-cholesteryl oxy carbonyl)benzaldehyde with different substituted aromatic and heterocyclic amines. The molecular structures of the compounds were confirmed by Fourier transform infrared (FT-IR), 1H, and 13C nuclear magnetic resonance spectra. The mode of linkage has been made via ‒COO‒ and ‒C˭N‒ bonds. The linkages and different substituted aromatic and heterocyclic groups were undertaken to study their influence on the isotropization temperature (Ti) and on mesomorphic property. The thermal phase behavior of the synthesized compounds was investigated by polarizing optical microscopy coupled with hot stage and differential scanning calorimetry (DSC). Enantiotropic cholesteric phase were shown by 4′-[3-Cholesteryloxycarbonyl]benzylidene- 1, 2, 4- triazine-3-yl and monotropic nematic mesophase were shown by 4′-[3-Cholesteryl oxycarbonyl]benzylidene-(4- methyl)aniline whereas 4′-[3-Cholesteryloxycarbonyl] benzylidene-(4-butoxycarbonyl)aniline defined oily streak phase in heating cycle. The remaining members of the series exhibited monotropic droplet texture in cooling cycle with exclusive suppression of cholesteric phase.

Methylene-linked liquid crystal dimers and the twist-bend nematic phase

The transitional properties of three methylene-linked liquid crystal dimers are reported, namely, 1,5-bis(4-cyanoanilinebenzylidene-4′-yl)pentane (CN-5-CN), 1,5-bis(4-methoxyanilinebenzylidene-4′-yl)pentane (1O-5-O1), and 1,5-bis(4-ethoxyanilinebenzylidene-4′-yl)pentane (2O-5-O2). Each dimer exhibits two monotropic mesophases. The higher temperature mesophase is a normal nematic phase while the lower temperature phase is assigned as a twist-bend nematic phase. The assignment of the twist-bend nematic phase was based on the strong similarities in the optical textures observed to those reported recently for a structurally similar dimer. The complete miscibility of the mesophases exhibited by CN-5-CN and 1O-5-O1 has been established. The analogous hexamethylene-linked dimers exhibit only the normal nematic phase as do the corresponding ether-linked dimers. A review of the literature reveals another five methylene-linked odd-membered dimers that exhibit a nematic–nematic transition and, in each, the lower temperature nematic phase exhibits similar properties to those reported for the twist-bend nematic phase. The formation of this new nematic phase has been attributed to a negative bend elastic constant which results from the bent geometry of methylene-linked odd-membered dimers.

Self‐Assembly of a Low‐Symmetry Monodendron Containing Two Asymmetrically Linked Molecular Wedges

Herein, we describe the synthesis of a low-symmetry monodendron, 3,4-bis(dodecyloxy)-5-[3,4,5-tris(dodecyloxy)benzyloxy]benzoic acid, following a simple route which starts from gallic acid ethyl ester and does not require any protecting groups. The self-assembled structures formed by the compound in 3D and 2D were investigated by synchrotron X-ray scattering and scanning force microscopy (SFM). In 3D, the compound forms a stable crystalline phase with an orthorhombic lattice in which the alkyl chains connected to different benzene rings form crystalline and amorphous domains. Upon cooling from the isotropic melt the compound exhibits a monotropic smectic mesophase. In 100-nm-thick films on a neutral substrate the structure loses its biaxiality, adopting a hexagonal columnar structure with the columns oriented parallel to the substrate. By contrast, in ultrathin films on graphite the SFM likely reveals two crystal orientations, which can develop due to the epitaxial adsorption on the substrate of the alkyl chains pertinent to different benzene rings.

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.

ChemInform Abstract: Columnar Mesophases of Cyclic Trimers of Disubstituted Acetylenes.

Hexa(4-alkyphenoxymethyl)benzenes, 4(with n= 4, 7, 9) were prepared by the alkylation of hexa(bromomethyl)-benzene and/or Cp2Co catalysed cyclotrimerization of the corresponding 1,4-di(4-alkylphenoxy)but-2-yne monomer, 2. The derivative 4(n= 4) is crystalline. The derivative 4(n= 7) displays an enantiotropic columnar mesophase and compound 4(n= 9) displays a monotropic columnar mesophase whose polarized optical microscopic textures are typical of Dho mesophases. An additional columnar mesophase of the derivative 4(n= 7) is monotropic. Hexa(4-alkoxyphenyl)benzenes, 3(n= 4–9) were prepared by PdCl2(PhCN)2 catalysed cyclotrimerizations of the corresponding 1,2-di(4-alkoxyphenyl)acetylenes, 1. The derivatives 3(n= 6–9) form anisotropic glasses whose columnar mesophases become more fluid as the temperature approaches isotropization. Methyl branches in either the mesogen or the alkoxy substituents promotes solidification, whether it is to a crystalline phase or to an anisotropic glass.

Synthesis and thermotropic behaviour of imidazole-terminated liquid crystals

Two novel liquid crystals containing terminal imidazole groups (Imi-COOH and Imi-DAH) were designed and synthesised. Imi-COOH exhibits a high-temperature monotropic smectic mesophase that is substantially stabilised by hydrogen bonding between acid and imidazole end-groups. Despite its rigid diacylhydrazine core, which offers the capability of forming lateral hydrogen bonds, Imi-DAH exhibits a nematic mesophase. Fourier transform infrared analysis suggested that the terminal imidazole group interferes with lateral hydrogen bonding between diacylhydrazine cores and destabilises the smectic mesophase. Future studies will examine how proton transport is affected by anisotropic mesophases.

Liquid Crystalline Properties of 3-[4-(4′-Alkoxybenzoyloxybenzylidene) amino]-1,2,4-triazines: Synthesis and Characterization

A new series of 3-[4-(4′-alkoxybenzoyloxybenzylidene)amino]-1,2,4-triazines, C3H2N3N˭CHC6H4OCOC6H4OCmH2m + 1 where m = 6, 7, 8, 9, 10, 11, 12, 14, and 16 have been synthesized. These compounds have been characterized by elemental analyses, FT-IR, UV-visible, 1H, and 13C NMR spectroscopy. Mesomorphic properties of these compounds were studied by differential scanning calorimetry and polarizing microscopy. The mesomorphic nature of these compounds is dependent on the alkoxy chain length. The compounds (m = 6, 7) do not exhibit mesomorphism while the compounds (m = 8, 9, 11, 12, 14) show a monotropic nematic mesophase in cooling cycle. The 3-[4-(4′-decyloxybenzoyloxybenzylidene)amino]-1,2,4-triazine displays an enantiotropic nematic mesophase and the hexadecyloxy compound exhibits the smectic A mesophase.