Synthesis and mesomorphic properties of mesogens containing 1,1,2,2-tetrahydroperfluorodecaoxy terminal chains

One series of two-ring and two series of three-ring mesogens with 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10-heptadecafluorodecaoxy terminal chains containing tolane or biphenyl units have been synthesized. Their mesomorphic properties were observed and measured by optical polarizing microscopy and differential scanning calorimetry. The three-ring mesogens only exhibit a wide smectic C phase when the length of their hydrocarbon chains is intermediate.     

Non-symmetric calamitic liquid crystal dimers containing troponoid and benzenoid units

Five types of non-symmetric calamitic dimers were synthesized to investigate the effect of the core structure and length of the spacer on mesomorphic properties. Two non-symmetric dimers containing a troponoid and benzenoid unit showed smectic A and C phases whereas the corresponding benzenoid dimers showed no mesophase. Non-symmetric dimers with a three-ring system showed smectic A and C phases with higher transition temperatures than the two-ring system. We propose packing models for these non-symmetric dimers by considering the direction of the dipole moments of the ring structures and microsegregation between the polar units and the non-polar chains.     

New bent core mesogens with exceptionally high clearing points

A homologous series of novel two-ring alkoxythiophene-containing liquid crystals has been synthesized using a recently developed cyclization methodology to construct the heterocyclic core. The new heterocyclic unit is expected to confer high negative dielectric anisotropy and high dielectric biaxiality when incorporated into suitable mesogenic structures. The materials reported here possess nematic phases, with the longer chain homologues displaying smectic mesomorphism. In all cases the clearing points are significantly enhanced when compared with other two-ring thiophene-based mesogens. The synthesis, mesomorphic behaviour and stability are discussed, and the mesomorphic behaviour is compared with the analogous 4-alkoxy-4′-cyanobiphenyl derivatives synthesized by Gray.     

New bent core mesogens with exceptionally high clearing points

A homologous series of novel two-ring alkoxythiophene-containing liquid crystals has been synthesized using a recently developed cyclization methodology to construct the heterocyclic core. The new heterocyclic unit is expected to confer high negative dielectric anisotropy and high dielectric biaxiality when incorporated into suitable mesogenic structures. The materials reported here possess nematic phases, with the longer chain homologues displaying smectic mesomorphism. In all cases the clearing points are significantly enhanced when compared with other two-ring thiophene-based mesogens. The synthesis, mesomorphic behaviour and stability are discussed, and the mesomorphic behaviour is compared with the analogous 4-alkoxy-4'-cyanobiphenyl derivatives synthesized by Gray.     

Polar nematic methyl (E)-[trans-4-cyclohexyl-substituted]allyl ethers: Synthesis, liquid crystal transition temperatures and some physical properties

We have introduced an oxygen atom and a carbon-carbon double bond with a trans-configuration (E) into the terminal alkyl chain attached to the cyclohexyl ring of a variety of two- and three-ring nematic liquid crystals of positive dielectric anisotropy. The new polar two-ring methyl (E)-allyl ethers often possess low melting points, but are not mesomorphic in general. The related three-ring methyl (E)-allyl ethers exhibit high clearing points and wide nematic ranges. Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. This is partially due to the low smectic transition temperatures observed for the methyl (E)-allyl ethers. Selected physical properties of three binary mixtures of a weakly polar standard nematic liquid crystal and three difluoro-substituted (polar) liquid crystals (including the new ethers) differing only in the nature of the terminal chain show that, although some of the methyl (E)-allyl ethers exhibit longer switch-off times in TN cells than those of analogous liquid crystals incorporating either a methyl propyl ether or a 1-(E)-propenyl chain instead of the methyl (E)-allyl ether chain, they are still useful components for nematic mixtures, especially where a wide temperature range is required.     

Synthesis and mesophase behaviour of mesogens bearing omega, alpha, alpha-trihydroperfluoroalkoxy end tails

One series of two-ring and two series of three-ring liquid crystal compounds, all containing omega, alpha, alpha-trihydroperfluoroalkoxy terminal tails, were prepared and characterized by IR, NMR, MS and elemental analysis. Their phase transition behaviour was investigated by DSC and polarizing optical microscopy. Biphenylene derivatives with the omega, alpha, alpha-trihydroperfluoroalkoxy end group form a stable smectic A phase. In the three-ring system, biphenylene ester compounds exhibit a smectic phase without a nematic phase. The compounds exhibit smectic A and smectic C phases when the terminal groups are intermediate length alkyl and fluorinated alkyl chains. Mesogens with fluorinated tails have a broader smectic C phase than the non-fluorinated mesogens.     

Alkyl/alkenyloxy phenyl/biphenylpyrimidines: Dependence of the liquid crystal transition temperatures on the position of the nitrogen atoms and the position and configuration of carbon-carbon double bonds

The influence on the transition temperatures of a carbon-carbon double bond in the terminal alkenyloxy (ether) chain of four series of three-ring phenyl/biphenyl-pyrimidines has been systematically investigated. The position and configuration of the double bond has been varied systematically in order to determine the optimal configuration and conformation of the terminal chains for smectic C formation. Four positions of the two nitrogen atoms were chosen. This produced four isomeric series of pyrimidines and differences in the mesomorphic behaviour were observed. The dependence of the transition temperatures on chain length was studied for the same four isomeric pyrimidine series. Comparisons between the new three-ring phenyl/biphenyl-pyrimidines and the corresponding two-ring phenylpyrimidines revealed almost identical tendencies. These results are consistent with a linearly-extended conformation of the chain. Several of the new ethers exhibit remarkably low viscosity values (i.e. short response times) and wide switching angles in an optically active base mixture used for evaluation and comparison purposes. Hence they can be used to widen the temperature range of mixtures designed for electro-optic display devices based on ferroelectric effects (FLCDs) without leading to longer response times.     

Intramolecular rearrangement of two-ring 2,2-disubstituted 4-oxo-1,2,3,4-tetrahydropyrimidines under the influence of polyphosphoric acid

Intramolecular rearrangement of two-ring 2,3-disubstituted 4-oxo-1,2,3,4-tetrahydropyrimidines to pyridine derivatives, which takes place under the influence of polyphosphoric acid, was observed. It is shown that cycloalkanopyrimidones are converted primarily to two- or three-ring 2-pyridones and to small amounts of the corresponding 4-pyridones and 4-aminopyridines. A possible mechanism that enables one to explain the difference in the occurrence of the rearrangements primarily to 2- or 4-pyridones as a function of the absence or presence of aromatic character of the ring condensed with the pyrimidine ring is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1549–1553, November, 1977.     

Structural assignment and molecular order of three-ring mesogen by 13C NMR spectroscopy in mesophase

A homologous series of rod-like molecules with three phenyl rings in the core and terminal alkoxy chains are synthesised from mesogenic two-ring aldehyde by coupling with non-mesogenic 4-alkoxy anilines. The mesophase properties are evaluated with hot-stage optical polarising microscopy and differential scanning calorimetry, and accordingly, all the molecules exhibited enantiotropic nematic and smectic C phases along with monotropic low-temperature smectic phases. For a representative homologue, the existence of smectic C phase is further confirmed by noticing a sharp reflection at small angle region in powder X-ray diffraction which varies with change in temperature. The main focus of the investigation, however, is the clear demonstration of chemical shift assignment of static ¹³C NMR of a representative three-phenyl ring mesogen in smectic C phase. In this novel approach, the static ¹³C NMR spectral data of synthetic mesogenic intermediate namely two-ring aldehyde are utilised for the chemical shift assignment of three-ring mesogens. Further, the orientational order parameter of two-ring aldehyde in smectic A and three-ring mesogen in smectic C phase is carried out by measuring the ¹³C-¹H dipolar couplings by 2D separated local field spectroscopy.     

Mesomorphic properties of 2-acyloxy5-(4-alkoxyphenylazo)tropones, 2-acyloxy-5-(4-alkylphenylazo)tropones, and 2-acyloxy-5-(4-alkoxycarbonylphenylazo)tropones

Three series of mesomorphic 2-acyloxy-5-phenylazotropones with alkoxy, alkyl, and alkoxycarbonyl groups at C-4 on the phenyl ring were prepared. It was known that the corresponding 5-phenylazotropolone derivatives and their methyl ethers were not mesomorphic. 2-Acetyl-5-(4-hexyloxyphenylazo)tropone, however, shows a monotropic smectic A phase. Even an acetyl group is therefore able to induce a mesophase. The effects of terminal substitution of the tropone ring by groups such as alkoxy, alkoxycarbonyl, and alkyl on the clearing points are discussed.     

Mesomorphic properties of 2-acyloxy5-(4-alkoxyphenylazo)tropones, 2-acyloxy-5-(4-alkylphenylazo)tropones,and 2-acyloxy-5-(4-alkoxycarbonylphenylazo)tropones

Three series of mesomorphic 2-acyloxy-5-phenylazotropones with alkoxy, alkyl, and alkoxycarbonyl groups at C-4 on the phenyl ring were prepared. It was known that the corresponding 5-phenylazotropolone derivatives and their methyl ethers were not mesomorphic. 2-Acetyl-5-(4-hexyloxyphenylazo)tropone, however, shows a monotropic smectic A phase. Even an acetyl group is therefore able to induce a mesophase. The effects of terminal substitution of the tropone ring by groups such as alkoxy, alkoxycarbonyl, and alkyl on the clearing points are discussed.     

Energy transfer in the nanostar: the role of coulombic coupling and dynamics

We present a theoretical investigation of energy transfer in the phenylene ethynelene dendrimer known as the nanostar. Data from extensive molecular dynamics simulations are used to model the dynamical effects caused by torsional motion of the phenyl groups. We compare rate constants for energy transfer between the two-ring chromophore and the three-ring chromophore obtained via the F?rster model, the ideal dipole approximation (IDA), and the transition density cube (TDC) method, which has as its limit an exact representation of the Coulombic coupling. We find that the rate constants obtained with the TDC are extremely sensitive to the phenyl group rotation, whereas the constants computed with the F?rster model and the IDA are not. The implications of these results for the interpretation of recent pump-probe experiments on the nanostar are discussed in detail. Finally, we predict the temperature dependence of the rate constant for energy transfer.     

Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.     

Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.     

Nematic compounds and mixtures with high negative dielectric anisotropy

Syntheses, mesogenic and dielectric properties of three-ring alkylcyclohexyl, alkoxy and alkylphenyl benzoates substituted with four fluorine atoms or with two fluorine atoms and simultaneously a cyano group or two cyano groups are described. Their properties are compared with analogous three-ring phenyl tolanes. Conformation analysis and the calculation of dipole moments with the quantum chemistry method are performed to explain the experimental results. Several four fluorine-substituted two-ring tolanes and biphenyls are also prepared, which are used as a solvent decreasing viscosity, melting point and clearing point of the formulated mixtures. Examples of mixtures prepared from the esters and tolanes with high dielectric anisotropy are given. Curiosity is observed that 4?-(4-ethoxyphenyl)-4-pentyloxy-2,2?,3,3?-tetrafluorotolane is not the mesogenic compound, while analogous ester 4?-ethoxy-2,3-difluorobiphenyl-4-yl 2,3-difluoro-4-pentyloxybenzoate exhibits a broad temperature range of the nematic phase.     

Synthesis and physical properties of laterally fluorinated liquid crystals containing 1,3,2-dioxaborinane and cyclohexyl units

Six series of laterally fluorinated liquid crystals containing 1,3,2-dioxaborinane and cyclohexyl units have been synthesized and characterized. Their mesomorphic properties were characterized by polarizing optical microscopy and differential scanning calorimetry. All these compounds are thermotropic liquid crystalline materials. All three-ring compounds (series A, B and C) and most four-ring compounds (series D, E and F) exhibit only a nematic phase, while some four-ring compounds with long terminal alkyl chains show nematic, smectic A and even smectic B phases. In addition, four compounds containing a 1,3-dioxane unit were prepared, and their mesomorphic properties compared with their 1,3,2-dioxaborinane analogues. The dielectric anisotropies of selected target compounds were determined; some showed a negative anisotropy. The relationships between the properties and chemical structures of these new compounds are discussed.     

Properties of thermotropic liquid crystals induced by hydrogen bonding between pyridyl-1,2,4-oxadiazole derivatives and benzoic acid, 4-chlorobenzoic acid or 4-methylbenzoic acid

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 3-(4-pyridyl)-5-(4-n-alkoxy)phenyl-1,2,4-oxadiazoles with benzoic acid, 4-chlorobenzoic acid or 4-methylbenzoic acid. Neither the oxadiazole derivatives nor the carboxylic acids are mesomorphic, but the H-bonded complexes are. Their liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction.     

The Synthesis and Liquid Crystal Properties of Some 2,5-Disubstituted Pyridines

The synthesis is reported of fifteen three-ring 2,5-disubstituted pyridines and two pyridine-N-oxides where the pyridine rings carry a variety of alkyl, aryl, cyclohexyl, cyclohexylethyl and fluorinated-aryl substituents. The mesomorphic transition temperatures for these compounds have been measured; all the compounds show enantiotropic phases. The different substituent effects are discussed and comparisons are made with previous work on analogous systems where the hetero-function is replaced by C-F.     

焦炉降尘中多环芳烃的毛细管超临界流体色谱分析

研究了９个多环芳烃混合样品的超临界流体色谱分析条件，并与毛细管气相色谱法做了比较。超临界流体色谱的条件是：柱温１１０℃；程序升压９．０ＭＰａ（５ｍｉｎ）１．４ＭＰａ／ｍｉｎ２８．０ ＭＰａ。各组分保留时间的相对标准偏差为 １．４％～３．０％，定量分析的相对误差为１．４％～６．０％，比毛细管气相色谱法具有明显的优越性。试验了焦炉降尘样品，发现该样品主要由双环和三环的多环芳烃类物质组成。其中萘含量约占８０％。     

Influence of different spacers on the mesomorphic properties of 4-biphenyl derivatives within the F-alkylated series

In order to determine the influence of modification of the shape of the connector, within the fluorinated series, on the formation of mesophases in low molecular mass compounds, we decided to examine the mesomorphic behaviour of molecules which consist of a 4-biphenyl unit linked to a fluorinated tail via different spacers. The synthesis and the physical properties of these new materials are reported. The mesomorphic properties were characterized by polarized light microscopy and by differential thermal analysis, thereby showing the peculiar contribution of each of the spacers. The data collected from the 4-biphenyl derivatives synthesized allow us not only to confirm the enhancement of the smectic properties owing to the fluorinated alkyl chains, but also to display the impact of the spacer on these properties. Actually, some spacers like the amide or thioether type, as well as that of the hemithioacetal derivatives give suppression of the smectic character. Some others like that in the esters with an OC(O) spacer lead to mesophase or a short range SmA phase, and others give rise to broad enantiotropic behaviour like that of the esters with a C(O)O spacer, and of the ether or thioester types. These last mentioned give mesomorphic behaviour over a wide temperature range.