Mesomorphic properties of some laterally fluorinated 4-alkyl,4'-oxoalkyl 1,1': 4',1'terphenyls

The liquid crystalline behaviour and nematic viscosities of a series of laterally fluorinated alkyl-oxoalkyl terphenyls are reported. The mesomorphic behaviour and nematic viscosity can be influenced by the position of the oxygen atom in the oxoalkyl chain as well as the position of lateral fluorination. Compounds have been synthesized that are suitable for use in ferroelectric smectic C (S*_C) mixtures; the switching properties of a four component mixture are also reported.     

Liquid crystals and life

The molecules of living systems invariably exhibit both thermotropic and/or lyotropic liquid crystalline properties. In some cases the mesophases formed by bio-materials have lamellar structures, whereas in other situations they form columnar phases. Many liquid crystal biomaterials are found in cell membranes, indicating that such structures have properties that are dependent on liquid crystallinity for their behaviour of a variety of bio-materials is discussed. function. In this article the mesomorphic     

New mesomorphic organocyclosiloxanes II. Thermal behaviour and mesophase structure of organocyclohexasiloxanes

Investigations of thermotropic phase transitions performed on organocyclosiloxanes [PhSi(O)OSiR]₆, where R is Me₃, Me₂(CH₂Cl) or Me₂(CH≃CH₂), have revealed that all these hexamers are mesomorphic compounds. The hexamers exhibit uncommon polymesomorphic behaviour forming two quite different mesomorphic structures. The molecular arrangement in the low temperature (LT) modification is characterized by two-dimensional (2D) long-range order with hexagonal packing. The X-ray diffraction pattern and peculiarities of molecular packing in the crystal lead us to suggest that the LT-mesophase is columnar, presumably of the Col_hd type. The LT-mesophase is formed by dimeric moieties, which associate with each other in column-like substructures, the ring planes not orthogonal to the stack axis. The high temperature (HT) mesophase is a plastic crystal (3D-order), where molecules take up positions in a face-centred cubic lattice. This is a very uncommon example of thermal behaviour for plastic crystals that provides a unique opportunity to bridge the gap between plastic crystalline and liquid crystalline mesomorphic behaviour. The thermal and structural properties of the mesophases depend upon the type of side groups of the hexamers. The size of the ring also affects the phase behaviour and the mesomorphic structure. This conclusion is consistent with data obtained by us earlier for cyclotetrasiloxanes.     

Cyclic versus linear siloxane liquid crystalline oligomers: phase behaviour

The phase behaviour of cyclic and linear liquid crystalline polysiloxanes containing two different cholesteric mesogens is reported. The thermal properties of the synthesized monomers and oligomers were investigated by polarizing optical microscopy and differential scanning calorimetry. The influence of the structure of cyclic siloxane on the mesomorphic properties of cyclic liquid crystalline polysiloxanes is discussed. Similar trends in the thermal transitions of cyclic and linear compounds containing the same mesogenic composition were observed, though the cyclic oligomers showed poorer mesomorphic properties as compared with their linear analogues.     

Cyclic versus linear siloxane liquid crystalline oligomers: phase behaviour

The phase behaviour of cyclic and linear liquid crystalline polysiloxanes containing two different cholesteric mesogens is reported. The thermal properties of the synthesized monomers and oligomers were investigated by polarizing optical microscopy and differential scanning calorimetry. The influence of the structure of cyclic siloxane on the mesomorphic properties of cyclic liquid crystalline polysiloxanes is discussed. Similar trends in the thermal transitions of cyclic and linear compounds containing the same mesogenic composition were observed, though the cyclic oligomers showed poorer mesomorphic properties as compared with their linear analogues.     

Synthesis and mesomorphic properties of perfluorinated rod-like liquid crystals with sulphur-containing spacers

In order to determine the influence of 'sulphur-containing' spacers on the formation of mesophases in low molecular mass compounds, we have examined the mesomorphic behaviour of molecules which consists of a 4-biphenyl unit linked to an unbranched fluorinated chain via a short spacer including at least a sulphur atom. The synthesis of these compounds has been carried out from 2-F-butylethyl iodide or from the 2-F-alkylethyl mercaptans in the case of the F-hexyl and F-octyl tails. The mesomorphic properties have been characterized by polarized light microscopy and by differential thermal analysis showing the peculiar contribution of each of the spacers. The influence of the fluorinated chain and the shape of the connector on the stability of the mesophases has been investigated. The compounds with a thioether or a hemithioacetal spacer showed no mesomorphic properties, whereas the structures with a thioester spacer showed a very interesting enantiotropic behaviour of the smectic A type over a wide temperature range. Furthermore from the series exhibiting liquid crystalline behaviour, increasing the number of fluoromethylene units simultaneously increases both the melting and the clearing temperature. These mesomorphic properties within the fluorinated series are compared with those of their monocatenar hydrocarbon homologues.     

Synthesis and mesomorphic properties of Cu-coordinating liquid crystalline polysilsesquioxanes with heptyl side groups

In order to study the influence of the concentration of a flexible group on the liquid crystal behaviour of copper-containing complexes, series of Cu-coordinated, beta-diketone-based liquid crystalline polysilsesquioxanes (abbr. H-DK-Cu) and random copolymethylsilsesquioxanes (abbr. Me-DK-Cu), have been synthesized by the hydrosilylation reaction of a vinyl-terminated beta-diketone and 1-heptene with the polyhydrosilsesquioxane (H-T) and with the random copolymethylhydrosilsesquioxane (Me-T), followed by reaction with Cu(NH₃)₄Cl₂. Their mesomorphic properties were investigated by differential scanning calorimetry and optical polarizing microscopy. The H-DK-Cu and Me-DK-Cu complexes with M_w of approximately 1 x 10⁴ are thermotropic liquid crystalline polymers and their clearing temperature and mesophase ranges are lower than those of the corresponding Cu-coordinated, beta-diketone-based liquid crystalline polymethylsilsesquioxanes (Cu-FBDKLCP) without the n-heptyl flexible group. However, their liquidity within the temperature range of the liquid crystal state is better. The results are mainly attributed to the heptyl, flexible side group.     

Structure–property study of new [1,2,3]-triazole liquid crystalline derivatives

The synthesis of a new type of liquid crystalline compound derived from 1,2,3-triazole was achieved using Wittig reaction. Polarised microscopy studies, X-ray scattering and differential scanning calorimetry analysis revealed that the target compounds exhibit enantiotropic liquid crystalline properties. Their mesomorphic behaviour is closely related to the nature of substituents in position N1 of the heterocycle, the length of the mesogenic core as well as the isomerisation nature (E/Z) of the double bond.     

Synthesis,characterization and thermal properties of 4,4'-bis(4-n-alkoxybenzoyloxy)benzylideneanilines and bis(4-benzylidene-4'-n-alkoxyaniline) terephthalates

Series of novel thermotropic liquid crystalline compounds which serve as models for mesogenic diols have been synthesized. The mesogen molecules are constructed from 1,4-disubstituted benzene rings linked through ester and azomethine units. Based on the number of phenyl rings, a tetrad or pentad classification has been assigned to the core molecule. The structures of these compounds were established by FTIR and NMR spectroscopy, while the mesomorphic behaviour has been confirmed using polarizing optical microscopy and DSC. All the compounds of the homologues series are mesomorphic in nature. The lower members of the series are nematogenic, while the higher members exhibit both nematic and smectic character, with high melting behaviour and wide mesophase ranges.     

New symmetric azomethinic dimer: the influence of structural heterogeneity on the liquid crystalline behaviour

The paper deals with the study of the thermotropic liquid crystalline properties of a new azomethinic symmetric dimer and some of its structural heterogeneous mixtures with one of its reagents. Their thermotropic behaviour was monitored by polarised light microscopy, differential scanning microscopy and variable temperature X-ray diffraction measurements. The influence of the structural heterogeneity on the mesomorphic behaviour was established and some similarities with the mesomorphic behaviour of the polydisperse polymers were underlined.     

Wide temperature range mesomorphic behaviour of highly fluorinated 15-membered macrocycles and their open trisulphonamide precursor

The mesomorphic properties of 15-membered azamacrocycles containing long hydrocarbon or highly fluorinated long chains have been explored along with those of their open precursors. The liquid crystalline behaviour is determined by the presence of different heteroatoms or long fluorinated chains and the substitution pattern of the aryl units of the sulphonamides. The presence of highly fluorinated long chains in the para position with regard to the sulphonamide group was found to favour the formation of smectic mesophases with wide temperature ranges. All of the mesophases were studied by polarizing optical microscopy and differential scanning calorimetry.     

Liquid crystalline polybutadiene diols with chiral thiol side-chain units

New chiral thiols with three aromatic rings and the azo group in the molecular core have been synthesized and grafted on polybutadiene diols backbone. The resulting diols possess the OH end groups promising for preparation of the liquid crystal ordered networks. The mesomorphic and physical properties of the synthesized thiols and resulting diols have been studied by polarizing optical microscopy, differential scanning calorimetry, X-ray studies and dielectric spectroscopy. The resulting side-chain diols show the liquid crystalline behaviour. The effects of side-chain structure of the thiols and density of grafting on the polybutadiene diols has been studied and discussed.     

Synthesis and mesomorphic properties of fishbone-like liquid crystalline polysilsesquioxanes V. Pd-coordinating, fishbone-like azo-based liquid crystalline polysilsesquioxanes

New kinds of Pd-coordinating azo-based liquid crystalline polysilsesquioxanes, Pd-H-FBA and Pd-C-FBA, have been synthesized first by hydrosilylation reactions of a vinyl-terminated mesomorphic azo compound with ladder-like homopolyhydrosilsesquioxane (H-T) and copolymethylhydrosilsesquioxane (MH-T) to produce fishbone-like, azo-based liquid crystalline polysilsesquioxanes H-FBA and C-FBA, respectively, followed by a further ortho -palladation reaction with palladium chloride. The mesomorphic properties have been investigated by DSC, optical polarizing microscopy and temperature-variable X-ray diffraction. It is found that their clearing temperatures, Tcl, are much higher and the mesophase ranges, Delta T,are much wider than those of the corresponding comb-like polymers with a single main chain by more than 100 C. This indicates that the double main chain structures of the title polymers have a positive effect on mesomorphic properties. The influence of the contents of Pd2 ions on the liquid crystallinity is also discussed.     

Synthesis and characterization of some new dimesogenic compounds

We have synthesized four different types of dimesogenic compounds involving the cholesteryl moiety as one of the mesogenic constituents, and have investigated their liquid crystalline properties. The molecular structures of these dimesogens have been confirmed by spectral analyses; they exhibit a rich polymorphism, as revealed by optical microscopic and differential scanning calorimetric observations. The studies show that the mesomorphic behaviour is sensitive to the nature of the terminal alkyl chains, and to the structure of the 'second mesogen' that is attached to the cholesteryl unit through a polymethylene spacer.     

New Schiff's bases containing 1,3,4-thiadiazole and 1,3,4-oxadiazole units: a study of the effect of the heterocyclic ring and the position of the lateral alkoxy group on liquid crystalline properties

The synthesis of novel Schiff's bases incorporating the five-membered 1,3,4-thiadiazole (series 7, 9) and 1,3,4-oxadiazole (series 8, 10) rings have been prepared and their liquid crystalline properties studied. All compounds of series 7 exhibit an enantiotropic smectic C phase. No liquid crystalline properties were observed for the compounds of series 8-10. A study of the structure/mesomorphic activity relationship is also described.     

Synthesis and characterization of side‐chain liquid‐crystalline poly(ethyleneimine)s with cyanobiphenyl groups

A series of polyethyleneimine‐based side‐chain liquid‐crystalline polymers substituted with different ratios of cyanobiphenyl as pendent mesogenic groups has been synthesized in which the spacer length varies between two and six methylene units. The structures of the synthesized polymers are confirmed by infrared and ¹H nuclear magnetic resonance spectroscopy. The thermal properties of these polymers have been investigated using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. The results indicate that the thermal behaviour of the polymers is strongly dependent on the degree of substitution. Polymers containing more than 69% of mesogenic groups exhibit nematic‐type thermotropic liquid‐crystalline behaviour with schlieren textures. Below this limit, the polymers are amorphous. Polymers with a higher degree of substitution present the crystalline states. The phase transition temperatures increase and the mesomorphic temperature ranges widen with increasing degree of substitution. The clearing temperatures decrease as the spacer length increases. An odd–even effect in the clearing temperatures is observed and the odd members display the higher values.     

Non-symmetric liquid crystal dimers based on 1,3,4-oxadiazole derivatives: synthesis,photoluminescence and liquid crystal behaviour

A series of non-symmetric liquid crystal compounds consisting of two different semi-rigid anisometric cores, namely 1,3,4-oxidiazole and biphenyl units, and two short terminal groups, have been synthesised in good yield. It has been shown by polarising optical microscopy and differential scanning calorimetry that all these compounds display liquid crystalline behaviour, with nematic and/or smectic A mesophases. The nature of the mesophases is dependent on the electronic properties of the terminal groups. In methylene chloride solution all the compounds displayed a room temperature emission with λ_max at 358–396 nm and quantum yields of 0.29–0.56. The effect of the terminal groups on the mesomorphic and photoluminescent properties is briefly discussed in the context of their electronic characteristics.     

Effect of alkyl chain length in the terminal ester group on mesomorphic properties of new chiral lactic acid derivatives

Two series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic C_A* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour.     

Electroluminescent segmented liquid crystalline trimers

The synthesis and liquid crystal behaviour of light‐emitting trimeric liquid crystals consisting of three mesomorphic moieties connected by aliphatic spacers are reported. The combination of an aromatic light‐emitting central core and two cholestanyl (dihydrocholesteryl) groups induces a helical liquid crystalline phase with circularly polarised photoluminescence and electroluminescence. These segmented trimers are designed to possess a high glass transition temperature below which the structure of liquid crystalline phases can be fixed. The effects of odd and even spacers, spacer length and the presence of large lateral substituents on the liquid crystal behaviour and the glass transition temperature of these trimers were studied. Electroluminescence from a segmented liquid crystalline trimer is reported for the first time.     

New Schiff's bases containing 1,3,4-thiadiazole and 1,3,4-oxadiazole units: a study of the effect of the heterocyclic ring and the position of the lateral alkoxy group on liquid crystalline properties

The synthesis of novel Schiff's bases incorporating the five-membered 1,3,4-thiadiazole (series 7, 9) and 1,3,4-oxadiazole (series 8, 10) rings have been prepared and their liquid crystalline properties studied. All compounds of series 7 exhibit an enantiotropic smectic C phase. No liquid crystalline properties were observed for the compounds of series 8-10. A study of the structure/mesomorphic activity relationship is also described.