摘要:

Six series of a family of non-symmetric dimers, the α-(4-cyanobiphenyl-4′-yloxy)-ω-(4-n-alkylanilinebenzylidene-4′-oxy)alkanes, have been prepared. In three of the series, the number of methylene groups in the flexible alkyl spacer has been varied from 3 to 12 while the terminal alkyl chain is held constant at either 2, 6 or 10. In the remaining series, the effect of increasing the terminal chain length has been studied by holding the spacer length constant at 3, 4 or 5 methylene units while varying the length of the terminal chain from 0 to 10 carbon atoms. The phase behaviour and transitional properties of these series have been investigated using optical microscopy and differential scanning calorimetry, while the structures of the mesophases have been studied using X-ray diffraction on both powder and aligned samples. This study has revealed novel phase behaviour involving intercalated smectic phases stabilized by the mixed mesogenic group interaction. We have identified the first examples of intercalated smectic C, smectic I, crystal B and crystal J phases and have assigned the layer stacking sequences in the crystal B phases. An extension to the current nomenclature used to describe smectic phases is proposed in order to include these new structural modifications such that, for example, SAc, refers to the intercalated smectic A phase. The specific interaction between the two unlike groups has a much smaller influence on the nematic-isotropic transition temperatures than it has on the structures of the smectic phases. Quantitative estimates of the nematic-isotropic transition temperatures based on the Marcelja-Luckhurst theory provide further evidence for a specific interaction between the unlike mesogenic groups. Finally, the thermal behaviour of binary mixtures of the analogous symmetric dimers is also found to be governed by the mixed core interaction and intercalated smectic phases are observed in these mixtures.

ISSN:0267-8292    

DOI:10.1080/02678299408036531

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The hexa-4-dodecyloxybenzoyl derivative1of azacrown[18]-N6was originally reported to have a ‘tubular’ mesophase on the basis of its large central ring and 6-fold symmetry. Starting in the mesophase, annealing of1under a cover slip results in formation of a new crystalline phase that melts directly to an isotropic liquid at the temperature previously observed for the mesophase to isotropic transition. Thus the phase behaviour of1is kinetically controlled. The analogous hexa-3,4-bisdodecyloxybenzoyl derivative2of azacrown[18]-N6has no kinetic limitations to its phase changes and has an enantiotropic columnar liquid crystalline phase. We have synthesized side chain copolysiloxanes with a (CH2)11spacer and 75–84 per cent by weight of the same 4-dodecyloxybenzoyl-[18]-N6mesogen. The polysiloxanes also display a liquid crystalline phase.

ISSN:0267-8292    

DOI:10.1080/02678299408036532

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The lyomesomorphic behaviour in apolar organic solvents of members of two series1and2of disc-shaped palladium organyls—the syntheses of four of them are new (1d, fand2a, e) and are described here—each carrying twelve long lipophilic chains have been studied. Their lyomesomorphism appeared to be complex and has been observed here for the first time with metal organyls. As can be seen by polarizing microscopy, most of the binary mixtures investigated here exhibitnematicproperties. For two members of series1—the chloro-bridged1band its bromo-analogue1c—there is even evidence for the existence oftwodifferent nematic lyomesophases side by side showing reversible transitions between them. In ternary systems, i.e. after the addition of 2,4,7-trinitrofluorenone (TNF, a strong electron acceptor), the nematic phases are stabilized, suggesting that their mesophase structures are made up by columns with intercalated TNF molecules (charge transfer complex formation). Influences of structural features of the pallado-mesogens on the one hand and of the type of solvent on the other on the molecular self-aggregation in the observed types of lyotropic mesophase formed are discussed in detail.

ISSN:0267-8292    

DOI:10.1080/02678299408036533

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The disc-shaped tetra-palladium organyl1forms optically active charge transfer complexes in equimolar mixtures with the enantiomers of the π-acid electron acceptor2, (+)- or (−)-TAPA, exhibiting lyotropic cholesteric nematic properties in apolar organic solvents. These ternary systems are the first examples in which such a lyomesophase has been induced by charge transfer interactions.

ISSN:0267-8292    

DOI:10.1080/02678299408036534

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A range of 2,3-difluoro-substituted biphenyls incorporating a cyclohexylmethoxy unit as one terminal chain has been prepared and these materials are compared to the analogous compounds already reported with a dimethylene linking group. Related, directly-linked cyclohexylbiphenyls and some open-chain analogues have also been prepared which add to the diversity of the compounds reported. These were prepared as host materials of low birefringence for ferroelectric (S*c) mixtures and in general, the compounds have quite high Scphase stability. Metallation procedures have been used to prepare arylboronic acids which were employed in palladium-catalysed cross-coupling reactions to provide good yields of liquid crystal materials. The synthesis and transition temperatures of these compounds are discussed and compared with each other and with other selectedortho-difluoro-substituted systems.

ISSN:0267-8292    

DOI:10.1080/02678299408036535

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A series of 3-fluorinated 4-alkoxystilbazoles (n-3F-OPhVPy) and some of the related 2-fluorinated derivatives (n-2F-OPhVPy) have been synthesized; unlike their non-fluorinated counterparts, these new stilbazoles are non-mesomorphic. A single crystal structure determination of 3-fluoro-4-undecyloxy-4′-stilbazole shows the molecule to be planar,transwith respect to the double bond and to crystallize in only one of two possible extreme rotational conformers. Reaction of these fluorinated stilbazoles with [IrCl(COD)]2under CO affords the complexescis-[IrCl(CO)2(n-XF-OPhVPY)] which are non-mesomorphic for X = 3, but have monotropic phases for X = 2.

ISSN:0267-8292    

DOI:10.1080/02678299408036536

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The conformations of flexible chain molecules incorporated in a nematic environment have been investigated. The phase behaviours and orientational characteristics of 1,2-dimethoxyethane (DME) dissolved in 4′-methoxybenzylidene-4-n-butylaniline at low solute mol fraction have been reported in our previous paper. In this work, proton–proton and carbon–carbon dipolar coupling constant measurements were attempted in addition to2H NMR observations of quadrupolar splittings. These conformation-dependent properties were analysed according to the rotational isometric state (RIS) simulation scheme previously proposed. Our treatment rests on the assumption that the molecular axis of the chain should tend to align along the nematic field. Studies were further extended to a mixture of 1,2-diphenyloxyethane (DPE) with a nematic liquid crystal, 4,4′-azoxyanisole. Replacement of the terminal methyl groups in DME by phenyl groups leads to DPE. The results of the analysis indicate that the fraction of elongated conformers such asttttends to increase significantly on going from the isotropic to the liquid crystalline solution: DME; 9·4 to 15·6 per cent and DPE; 12·3 to 20·0 per cent. Thetgtform (tg+tortg−t) is the lowest-energy arrangement of these molecules. The fraction of this conformer also increases in DPE (26·8 to 40·0 per cent), while it decreases in DME (25·7 to 18·8 per cent). The conformational distributions of chain molecules were found to remain invariant over the range of concentration (0·5–6·0 mol per cent) and temperature (22·0–44·5°C) studied. It has been concluded that the observed variation of proton dipolar and deuterium quadrupolar couplings with concentration and temperature mainly arises from the orientational order of the molecular axis, which varies sensitively with the alignment of the surrounding solvent molecules. These results suggest that flexible chains are also participating in the nematic interaction by adjusting their configurations so as to enhance favourable interactions and suppress unfavourable steric repulsions when accommodated in an anisotropic potential field.

ISSN:0267-8292    

DOI:10.1080/02678299408036537

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Errors in the calculations of Cheung and Emsley (Liquid Crystals,13, 265 (1993)) used to derive the populations of α,δ-bis(phenoxy)ethane dissolved in isotropic and nematic liquid crystalline solvents have been corrected, and the results are compared with those obtained on the same molecule by Abe, Iizumi and Kimura (Liquid Crystals,16, 655 (1994)). The principal difference between these two calculations is that Abeet al., obtain 0·80 as the population of thetg±tconformers, and they find this to be independent of temperature, whereas the present calculations obtain 0·42 to 0·58 depending upon solvent and temperature.

ISSN:0267-8292    

DOI:10.1080/02678299408036538

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Discotic β-diketonate liquid crystals containing palladium(II), and oxovanadium(IV), (V≡0), analogous to known copper complexes (which display discotic lamellar and columnar mesophases), have been prepared and characterized. These are the first enantiotropic discotics containing Pd(II) and among the earliest examples containing VO(IV). The best-behaved Pd(II) complex is [Pd(DK 10, 10)2], and it also is probable that the complexes [Pd(DKn,n)2] (n= 7–9) are mesomorphic, however their characterization is difficult due to decomposition in the isotropic phase. The mesophase of [Pd(DK 102,102)2], which appears below 100°C, is suggested to be an example of the rare Ndphase on the basis of optical microscopy. The complex [VO(DK8,8)2] is an enantiotropic discotic vanadyl complex; the monotropic behaviour of [VO(DK 10,10)2] was also confirmed. It is suggested that the discotic phase which occurs for [VO(DK 8,8)2] is more organized than that of [Cu(DK 8,8)2].

ISSN:0267-8292    

DOI:10.1080/02678299408036539

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The mesophase electrostatic stabilization energy (E) has been examined by using the ionic continuous solid solution model for binary systems of sodium and potassium alkanoates with a common anion. It is found thatEincreases with a decrease in chain length of the alkanoate anion and that there is an inverse proportionality betweenEand the square of the mesophase bilayer spacing. The electrostatic stabilization factor is shown to be responsible for the formation of an ionic mesophase in binary acetate and propionate systems derived from two non-mesomorphic components.

ISSN:0267-8292    

DOI:10.1080/02678299408036540

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor