Novel oxazepinedione-derived symmetric dimers: synthesis and mesophase characterisation of seven-membered heterocyclic compounds

The synthesis and characterisation of three sets of symmetric dimeric compounds composed of seven-membered oxazepinedione heterocyclic rings were carried out. All the dimers possess the tetradecyl- (n = 14) alkyl side chain attached to the nitrogen atom of the oxazepinedione core. The oxazepinedione core in turn was connected with varied connecting spacers (n = 4, 6, 8, 10 and 12). The dimers were spectroscopically characterised by FT-IR, ¹H-NMR, ¹³C-NMR and elemental analysis techniques. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry and polarising optical microscopy with heating assembly. The precursor imines 2a–e itself started exhibiting liquid crystalline SmA/tilted hexatic mesophase. Further fusion of 2a–e with maleic anhydride, succinic anhydride and phthalic anhydride gave the novel oxazepinedione-derived symmetric dimers 3a–e, 4a–e and 5a–e respectively. The dimers 3a–e and 4a–e did not exhibit any liquid crystal (LC) properties. However, the phthalic anhydride-fused oxazepinediones 5a–e show monotropic nematic liquid crystalline phase. The results indicate that the formation of mesophase is dependent on the type of fused oxazepinedione ring.     

Heterocyclic pyridine-based liquid crystals: synthesis and mesomorphic properties

A series of new calamitic liquid crystals, 4-{[(pyridin-4-yl)methylidene]amino}phenyl 4-alkoxybenzoates comprising a heterocyclic (pyridine) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were synthesised and characterised. This series consists of nine members wherein the members differ by the length of alkoxy chain (C_nH_2n+1O–, where n = 2, 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviours were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first three members of the series (n = 2, 4 and 6). As the alkoxy chain increased to n = 8 and n = 10, the nematic phase appeared together with an additional smectic A (SmA) phase. When moving from n = 12 until the highest members (n = 18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA).     

Investigation of liquid crystalline property of a new calamitic liquid crystalline system methyl 4-(4ʹ-(4ʹʹ-(decyloxy)benzyloxy) benzylideneamino)benzoate

A new polar calamitic liquid crystal, methyl 4-(4?-(4?-(decyloxy)benzyloxy) benzylideneamino)benzoate (M3BA) containing ether and Schiff base groups as linker with terminal polar ester group, has been synthesised and mesomorphic properties are studied by differential scanning calorimetry, polarising optical microscopy, density functional theory, temperature-dependent X-ray diffraction and temperature-dependent micro- Raman study. The smectic A (SmA) mesophase with focal conic texture has been observed with wide mesomorphic range. Layer thickness in SmA phase is greater than the optimised length of the molecule, indicating partially bilayer SmA phase. Analysis of Raman marker bands of C–H in-plane bending of phenyl rings, C=C stretching of rings, C=N stretching and C=O stretching shows structural changes at molecular level at Cr → SmA phase transition and provides proper intermolecular interactions responsible for dimeric unit in partially bilayer SmA phase.     

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.     

Esters derived from 7-decanoyloxychromone-3-carboxylic acid: synthesis and mesomorphic properties

The synthesis and liquid crystalline properties of a new series of calamitic liquid crystals containing 4-H-benzopyran-4-one (chromone) within the central core is reported. The first homologue in the series display SmA phase (8a), the homologues (8b-e) exhibit SmA and SmC mesophases and the homologues (8f-h) exhibit only a SmC mesophase.     

A study on the effect of carboxylate ester and thioester linking groups in ferroelectric liquid crystal dimers

Two series of symmetrical liquid crystal twins possessing a chiral centre at the inner side of the molecules were synthesized and characterized. Structural effects on the mesomorphic and physical properties were investigated in terms of (a) variation of carboxylate and thioester groups linking the spacer and core, (b) variation in achiral chain length between two mesogenic units. The mesomorphic investigation reveals that these compounds exhibit a BP, N*, SmA* and SmC* mesophase sequence for the BDPNP series, and a SmA and SmC* sequence for the ABPNTP-n series. The P_s values were measured and a largest of 38.5 nC cm^-2 was observed for ABPNTP-12.     

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.     

Synthesis, mesomorphic properties and structural study by semi-empirical calculations of amides containing the 1,3,4-thiadiazole unit

The synthesis and liquid crystalline properties of a new series of amides (series 2a-f , 3a-d and 4a-d ) incorporating pyridine and 1,3,4-thiadiazole rings are reported. No homologues of the series 2 show mesomorphic properties. In the series 3 only the highest homologues ( 3d ) displays an enantiotropic SmA mesophase; the compound 3c exhibits a monotropic SmA mesophase, and the homologues 3a , b display no liquid crystal properties. The amides 4b-d display an enantiotropic SmA phases and the first homologue ( 4a ) exhibit only crystalisotropic transition. These series are compared with previously reported Schiff's bases and amide analogues. A structural study by AM1 semi-empirical calculation is also described.     

Esters derived from 7-decanoyloxychromone-3-carboxylic acid: synthesis and mesomorphic properties

The synthesis and liquid crystalline properties of a new series of calamitic liquid crystals containing 4-H-benzopyran-4-one (chromone) within the central core is reported. The first homologue in the series display SmA phase (8a), the homologues (8b–e) exhibit SmA and SmC mesophases and the homologues (8f–h) exhibit only a SmC mesophase.     

EPR anisotropy induced by a magnetic field in the smectic A phase of a mesogenic Cu(II) complex derived from a Schiff's base

The Q-band electron paramagnetic resonance (EPR) spectrum of the frozen smectic phase of the mesogenic compound bis[N -(4'-n-pentoxyphenyl)-4-n-decyloxysalicylaldiminate] copper(II) is studied. An anisotropic EPR spectrum is observed if freezing from the SmA phase is done in the presence of a magnetic field; the sample tends to orient with the director perpendicular to the magnetic field. The relative intensities of the EPR signal of this exchange coupled system are discussed in relation to the orientational distribution of the molecules. The results appear to be compatible with a biaxial magnetic susceptibility in the SmA phase. This suggests that an ordering of the short axes of the molecules in the plane perpendicular to the director in the SmA mesophase may take place.     

分子间作用力对咪唑盐介晶相性质的影响

通过对咪唑环1位(N1)取代烷基、3位(N3)取代基及阴离子的修饰合成了一系列具有近晶A (SmA)相的咪唑类离子液晶. 利用差示扫描量热法、单晶衍射、小角度X射线衍射等手段研究了咪唑盐的介晶相温度范围、介晶态的结构, 并测量了部分咪唑盐的各向异性导电率. 结果表明, 咪唑环N1取代烷基、N3取代基及咪唑盐的阴离子会改变分子间范德华力和氢键, 从而对咪唑盐的介晶相性质产生影响. 此外, 当乙烯基引入到咪唑环N3位置时, 咪唑盐相邻的层结构之间形成π-π堆积作用, 不仅有利于介晶态的形成, 同时使氟硼酸类离子液晶具有最大的层间距和最小的各向异性导电率. 这一结果表明, 调控离子液晶的性质时必须综合考虑各种分子间作用力的影响.     

Hole mobility and lifetime in a smectic liquid crystalline photoconductor of a 2-phenylnaphthalene derivative

We have investigated hole transport properties in the smectic mesophases of a 2-phenylnaphthalene derivative 6-(4'-octylphenyl)-2-dodecyloxynaphthalene in detail by using time-of-flight technique. The transient photocurrents were measured in liquid-crystal cells with various thickness from 5 to 700 microm. They were well defined and nondispersive in the smectic A (SmA) phase up to 500 microm and in the smectic B (SmB) phase within the entire thickness employed, while they exhibited an exponential decay in the SmA phase at 700 microm. The mobilities in the SmA and SmB phases were constant in each mesophase irrespective of the cell thickness, and were 2.5 x 10(-4) and 1.7 x 10(-3) cm2V s, respectively. The hole lifetimes were determined to be 10 ms and longer than 5 ms for the SmA and SmB phases, respectively. We discuss the origin of these lifetimes from the two points of view, i.e., hole trapping by a trace amount of existing impurities and recombination with negative ionic charges. We conclude that impurities are mainly responsible for the present hole lifetime test.     

Insight into Out-of-Layer Fluctuations in the Smectic A Stability of 3,5-Diarylisoxazole Liquid Crystals

Polar-terminated 3,5-diarylisoxazole liquid crystals (ILCs) were synthetized and characterized. ILCs are composed by rigid core 3,5-diarylisoxazol, alkyl chain and polar-terminated flexible spacer. Hydroxyl-, ketal- and 1,2-diol-terminated ILCs rendered smectic C and A mesophase, while bromine-terminated ILCs showed smectic A and B mesophase, for monosubstituted and linear ILCs. For branched alkyl chain monotropic SmA was detected and for disubstituted ILCs no mesophase was detected. Out-of-layer fluctuations (OLFs) are discussed based on X-ray diffraction date and textures. The OLFs are dependent on the bromine atom hardness, hydrogen bonding through collective actions and conformational effects at the interface between layers. Smectic translational order parameter (TOP) Σ was also obtained for orientated bromine- and hydroxyl-terminated ILCs and related it with OLFs. For 1,2-diol-terminated ILCs two SmC sublayers were founded, probably related to the intramolecular hydrogen bond favoring the 5-membered and 6-membered formation.     

New liquid crystalline phases with layerlike organization

Novel lamellar mesophases which are quite distinct from conventional smectic mesophases were obtained with a bolaamphiphilic triblock molecule composed of a rigid biphenyl core, two polar 2,3-dihydroxypropoxy groups in the terminal 4- and 4'-positions, and a semiperfluorinated chain [O(CH2)6C10F21] in the lateral 3-position. The competitive combination of microsegregation and rigidity in this molecule leads to layer structures in which the bolaamphiphilic cores segregate from the lateral chains into distinct sublayers. In these sublayers the biphenyl cores are aligned parallel to the layer planes. Decreasing the temperature leads to a subsequent inset of orientational and positional order of the biphenyl unit, which leads to a transition from an uniaxial SmA phase to a biaxial SmAb phase and finally to a mesophase with an additional periodicity within the aromatic sublayers. Here, microsegregation occurs on two distinct levels: The segregation of the nonpolar chains from the aromatic cores leads to the "bulk" layer structure and segregation of polar and aromatic subunits within the aromatic sublayers gives rise to an additional periodicity within the aromatic sublayers. These phases can be regarded as smectic phases built up by quasi-2D layers with nematic, respectively SmA-like order, separated by isotropic layers of the lateral chains.     

SmA-SmC-B2 polymorphism in an achiral cyano substituted banana-shaped mesogen

A new achiral five-ring banana-shaped mesogen is presented which has a cyano substituent in the 4-position of the central core. Microscopical, X-ray, dielectric and electro-optical investigations give evidence for the unusual phase sequence B₂, SmC, SmA. The B₂ phase shows an antiferroelectric switching behaviour; the spontaneous polarization was found to be 330 nCcm^-2.     

Morphological phase behaviour under pressure of polycatenar mesogens with a perfluorinated moiety

Two polycatenar materials composed of a four-aromatic-ring core with a perfluorinated moiety attached in one terminal position through either butylene- or pentylene spacer groups, and three tetradecyloxy chains at the other end (abbreviated as 14PC₄F and 14PC₅F), were investigated to study the effect of pressure on the phase transition behaviour. A polarizing optical microscope equipped with a high pressure optical hot stage, was used for the purpose. The T vs. P phase diagrams of 14PC₄F and 14PC₅F were constructed in the pressure region up to 100 MPa. 14PC₄F showed the stable crystal (Cr₁)-columnar tetragonal (Col_tet)-smectic A (SmA)-columnar hexagonal (Col_h)-isoropic liquid (I) phase transition sequence under all pressures. 14PC₅F exhibited the phase sequence metastable crystal (Cr₂)-cubic (Cub)-Col_tet-SmA-I in a melt-cooled sample on heating under pressure. But when the melt-cooled Cr₂ sample was annealed at 52-54°C for 2-3 h, the stable crystal (Cr₁) was formed slowly, giving a stable Cr₁-Cub-Col_tet-SmA-I phase sequence. The temperature region of the stable cubic phase broadened with increasing pressure. Furthermore a new mesophase of 14PC₅F was pressure-induced between the I and SmA phases on cooling at pressures above about 16 MPa. Since the monotropic mesophase exhibited a texture very similar to that of the high temperature Col_h phase of 14PC₄F with planar orientation, the new phase was assigned at a high temperature columnar hexagonal phase of 14PC₅F.     

Synthesis and liquid crystalline investigation of chiral 6-alkoxy-2-naphathoic acid derivatives

A two new series of materials with a chiral fragment derived from ((S)-(─)-2-methyl-1-butanol and 6-alkoxy-2-naphathoic acid as the molecular core was synthesised and investigated. All the homologues exhibited enantiotropic mesomorphism. Chiral smectic C (SmC*), smectic A (SmA) and chiral nematic (N*) phases were observed in different homologues. All the compounds were characterised by spectroscopic and elemental analysis. Thermal investigations and mesophase characterisations for all the compounds were carried out by the combination of DSC and POM analysis. The effects of the central linkage and various terminal normal alkyl chains with its structurally related compounds have been discussed.     

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

Lateral n -alkanoyl substituents were introduced at the benzylic position of 2,5-bis\[4-( n -perfluoroheptyloctyloxy)benzoyloxy] toluene by free radical bromination followed by esterification with the corresponding potassium n -alkanoates. All of the transition temperatures of the resulting 2,5-bis\[4-( n -perfluoroheptyloctyloxy)benzoyloxy] benzyl n -alkanoates decrease relative to those of 2,5-bis\[4-( n -perfluoroheptyloctyloxy)benzoyloxy] toluene and with increasing length of the n -alkanoyl substituent. The SmC-SmA transition decreases the most, thereby stabilizing the SmA mesophase and destabilizing the SmC mesophase. In contrast to the well established concept that lateral substituents disrupt smectic layering, none of the 2,5-bis\[4-( n -perfluoroheptyloctyloxy)benzoyloxy] benzyl n -alkanoates exhibit a nematic mesophase.     

Reaction of 1-[2-(vinyloxy)ethyl]-1<Emphasis Type="Italic">H</Emphasis>-pyrroles with trifluoroacetic anhydride

Chemo- and stereoselectivity of the reaction of 1-[2-(vinyloxy)ethyl]-1H-pyrroles with trifluoroacetic anhydride have been studied. The reaction with an equimolar amount of trifluoroacetic anhydride chemoselectively involves the free α-position of the pyrrole ring with formation of the corresponding α-trifluoroacetylpyrroles. In the reaction with 2 equiv of trifluoroacetic anhydride, acylation of both α-position of the pyrrole ring and β-position of the vinyloxy group leads to the formation of 1-(2-{[(1E)-4,4,4-trifluoro-3-oxobut-1-en-1-yl]oxy}ethyl)-2-trifluoroacetyl derivatives with high stereoselectivity.     

Development of Polar Order in the Liquid Crystal Phases of a 4‐Cyanoresorcinol‐Based Bent‐Core Mesogen with Fluorinated Azobenzene Wings

A bent‐core mesogen consisting of a 4‐cyanoresorcinol unit as the central core and laterally fluorinated azobenzene wings forms four different smectic LC phase structures in the sequence SmA–SmC_s–SmC_sP_AR–M, all involving polar SmC_sP_S domains with growing coherence length of tilt and polar order on decreasing temperature. The SmA phase is a cluster‐type de Vries phase with randomized tilt and polar direction; in the paraelectric SmC_s phase the tilt becomes uniform, although polar order is still short‐range. Increasing polar correlation leads to a new tilted and randomized polar smectic phase with antipolar correlation between the domains (SmC_sP_AR) which then transforms into a viscous polar mesophase M. As another interesting feature, spontaneous symmetry breaking by formation of a conglomerate of chiral domains is observed in the non‐polar paraelectric SmC_s phase.