Mesomorphic behavior of new azomethine liquid crystals having terminal iodo group

A series of azomethine esters,3-hydroxy-4-{[（4-iodophenyl）imino]methyl}phenyl alkanoates possessing even number of carbon atoms at the terminal alkanoyloxy chain(C_n-1H_2n-1COO-,n = 4,6,8,10,12,14) was synthesized.n-Butanoyloxy was found non-mesogenic,whilst n-hexanoyloxy to n-tetradecanoyloxy exhibited enantiotropic smectic A phase with fan-shaped texture.It was found that the length of terminal alkanoyloxy chain influenced the mesomorphic properties.     

Heterocyclic benzoxazole-based liquid crystals:Synthesis and mesomorphic properties

New Schiff base liquid crystals containing benzoxazole core and alkanoyloxy chain at the end group of the molecules (C_n-1H_2n-1COO-,n=14,16,18) was synthesized.The present compounds are enantiotropic smectic A liquid crystals.It was also found that the end groups of the molecules and polar chloro substituent at the benzoxazole fragment had effect on the mesomorphic properties.     

Synthesis of new schiff base ester liquid crystals with a benzothiazole core

A series of new calamitic liquid crystals, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole core, terminal methoxy group and a Schiff base linkage were synthesised and characterised. This series comprises 12 members wherein members differ by the length of the alkanoyloxy chain (C _n-1H_2n-1COO-, where n?=?2–8, 10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. The short chain derivatives (n?=?2 and 3) were non-mesogenic compounds, while an enantiotropic nematic phase was present throughout the remaining members of the series. The smectic C phase emerged from the decanoyloxy derivative onwards.     

Calamitic liquid crystals of 1,2,3-triazole connected to azobenzene: synthesis,characterisation and anisotropic properties

Azobenzene-based calamitic liquid crystals, 4-((4-(4-methoxymethyl-1,2,3-triazol-1-yl)phenyl)diazenyl)phenylalkanoates have been isolated and their structures were characterised. The structure–property correlation with respect to the different alkanoyloxy terminal chain (–COOC_nH_2n+1 where n adopts odd numbers ranging from 3 to 15) has also been given attention in the present study. In this series, all compounds exhibit smectogenic properties. The lower homologues shows enantiotropic SmA phase as well as monotropic SmC phase. The higher homologues exhibit homeotropic alignment of smectic phases. These compounds possess very high anisotropic inclination in which the mesomorphic region covers nearly 80°C.     

Liquid crystalline properties of 4-isopropyl- and 4-isopropoxy- N -(4- n -alkoxysalicylidene)anilines

New homologous series of 4-isopropyl- and 4-isopropoxy- N -(4- n -alkoxysalicylidene)anilines were synthesized. The phase transitions of these homologues were determined by differential scanning calorimetry and polarizing optical microscopy. No enantiotropic liquid crystalline phases were observed for homologues having a terminal isopropyl group; as the terminal alkoxyl chain is lengthened, smectic C and nematic phases occur monotropically. The members with an isopropoxy substituent exhibit an enantiotropic nematic phase as the terminal alkoxyl chain is lengthened; the octyloxy member exhibits a monotropic smectic C phase as well as an enantiotropic nematic state.     

New mesogenic compounds possessing a biphenyl ester and ether moiety comprising 1,3-dimethylbarbituric acid: synthesis,characterisation and mesomorphic studies

New substituted derivatives of 5-vinyl-1,3-dimethylbarbituric acid were synthesised and evaluated for liquid crystal properties. Two sets of molecules were prepared. One end of all the molecules possesses the 1,3-dimethylbarbituric core. The first set comprises biphenyl ethers, 4a–n and the second set biphenyl esters, 5a–g. Liquid crystalline properties were investigated by POM and DSC techniques. All the compounds exhibited enantiotropic smectic A and nematic mesophases. The LC properties were found to depend on the spacer and terminal alkoxy- chain and alkoxy- ester moiety of the molecules. Smaller alkyl chain members showed a smectic phase, while higher alkyl chain members showed a nematic phase.     

Azomesogens containing an ethoxyethyl terminal chain: synthesis and characterization

Two homologous mesogenic series, the ethoxyethyl 4-(4'-n-alkoxyphenylazo)benzoates (I) and the ethoxyethyl [4-(4'-n-alkoxybenzoyloxy)phenylazo]-4'-benzoates (II), both containing a terminal ethoxyethyl chain, have been synthesized. In series I, all nine members synthesized exhibit only an enantiotropic smectic A mesophase. In series II, all 12 homologues exhibit an enantiotropic nematic mesophase; a smectic A phase appears in the n-butyloxy derivative as a enantiotropic phase and persists through to the n-hexadecyloxy member. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effects of the ethoxyethyl chain on mesomorphism.     

Synthesis and mesomorphic properties of Schiff base esters possessing terminal chloro substituent

<正>A homologous series of Schiff base esters,4-chlorobenzylidene-4'-n-alkanoyloxyanilines,containing even number of carbons at the end groups of the molecules(C_(n-1)H_(2n-1)COO-,n=4,6,8,10,12,14,16) were synthesized.The mesomorphic properties were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).It was found that the end groups of the molecules had an effect on the mesomorphic properties.n-Butanoyloxy was found non-mesogenic,whilst n-hexanoyloxy exhibited monotropic smectic phase.The higher members in this homologous series were enantiotropic smectogens.     

Monocyclic rod-type liquid crystals; 2,5-dialkanoyloxytropones and 5-alkanoyloxy-2-alkoxytropones

Two kinds of monocyclic troponoid mesogens, 2,5-dialkanoyloxytropones (4) and 5-alkanoyloxy2-alkoxytropones (5), were prepared. The former showed monotropic smectic A phases and the virtual isotropic liquid-smectic A transitions of the latter were determined by extrapolation of results in a binary phase diagram. Comparing the mesogenic properties between the tropones 4 and the 2-alkanoyloxy-5-alkoxytropones (1), the alkanoyloxy group at C-5 enhances both the melting points and the transition temperatures of the smectic A phases. From the comparison between 5 and 1 , the alkanoyloxy group at C-2 lowers the melting points.     

Monocyclic rod-type liquid crystals; 2,5-dialkanoyloxytropones and 5-alkanoyloxy-2-alkoxytropones

Two kinds of monocyclic troponoid mesogens, 2,5-dialkanoyloxytropones (4) and 5-alkanoyloxy2-alkoxytropones (5), were prepared. The former showed monotropic smectic A phases and the virtual isotropic liquid-smectic A transitions of the latter were determined by extrapolation of results in a binary phase diagram. Comparing the mesogenic properties between the tropones 4 and the 2-alkanoyloxy-5-alkoxytropones (1), the alkanoyloxy group at C-5 enhances both the melting points and the transition temperatures of the smectic A phases. From the comparison between 5 and 1, the alkanoyloxy group at C-2 lowers the melting points.     

Liquid crystals of 4-octyloxy-N-(benzylidene)aniline derivatives bearing trifluoromethyl or trifluoromethoxy end groups

Abstract

Seven new derivatives of 4-octyloxy-N-(4-substituted benzylidene) aniline have been synthesized. 4-Trifluoromethyl and 4-trifluoromethoxy derivatives exhibit stable smectic B and A phases, respectively, while both the 4-methyl and 4-methoxy derivatives have monotropic nematic phases. Fundamental liquid crystalline properties such as entropies of the phase transitions, microscopic textures, smectic layer spacings, orientational order parameters, and molecular dipole moments were determined. It has been revealed that moderately polar nature of these mesogens act to stabilizing monolayer smectic states. The smectic A phase of 4-trifluoromethoxy derivative exhibit very high orientational order. None of the disubstituted compounds, 3,5-bis(trifluoromethyl), 3,5-dimethyl, and 3,5-dimethoxy derivatives were mesogenic. The effect of terminal trifluoromethylation on the liquid crystalline properties is discussed.     

Columnar Phases from Covalent and Hydrogen-Bonded Liquid-Crystalline Ferrocene Derivatives

The synthesis and liquid-crystalline properties of tetracatenar covalent and H-bonded bis-ferrocene derivatives 1 and 2 , respectively, are reported. Both compounds gave rise to enantiotropic columnar liquid-crystalline behavior with a hexagonal molecular organization. To explore the possibility to obtain also calamitic liquid-crystalline phases from H-bonded ferrocene-containing liquid crystals, a rod-shaped ferrocene mesogen 3 was synthesized, which gave rise to enantiotropic smectic C and smectic A phases. For the first time, a rational synthetic design at the ferrocene level led to ferrocene-based liquid-crystals with columnar behavior and to H-bonded metallomesogens.     

Asymmetric dimeric liquid crystals The preparation and properties of the α-(4-cyanobiphenyl-4'-oxy)-ω-(4-n-alkylanilinebenzylidene-4'-oxy)hexanes

Abstract

The first eleven members of the homologous series of α-(4-cyanobiphenyl-4'-oxy)-ω-(4-n-alkylanilinebenzylidene-4'-oxy)hexanes have been synthesized. The compounds are all enantiotropic nematogens and, with the exception of the heptyl, octyl and nonyl homologues, exhibit smectic phases. The thermal stability of the smectic A phase initially increases with the length of the terminal alkyl chain, passes through a maximum and then falls dramatically before disappearing. The smectic A phase subsequently reappears with the decyl homologue which has the highest smectic A-nematic transition temperature of the series. In order to understand this unusual behavior we have determined the entropies of transition for the compounds and we have measured the layer spacing of the smectic A phase for three of them.     

The mesomorphic anomaly of 4-[2-(4-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl] phenyl trans-4-pentylcyclohexyl-1-carboxylates

Four homologous series of 4-[2-[4-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl] phenyl trans-4-alkylcyclohexyl-1-carboxylates have been prepared. Their liquid crystalline behaviour was investigated by optical polarizing microscopy and DSC. Series A, B and C exhibit the nematic phase. The phase transition behaviour of series D is anomalous. The compounds of series D with a short alkoxy chain exhibit enantiotropic smectic A and nematic phases, while those with a long alkoxy chain exhibit only the nematic phase.     

The mesomorphic anomaly of 4-[2-(4-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl] phenyl trans-4-pentylcyclohexyl-1-carboxylates

Four homologous series of 4-[2-[4-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl] phenyl trans-4-alkylcyclohexyl-1-carboxylates have been prepared. Their liquid crystalline behaviour was investigated by optical polarizing microscopy and DSC. Series A, B and C exhibit the nematic phase. The phase transition behaviour of series D is anomalous. The compounds of series D with a short alkoxy chain exhibit enantiotropic smectic A and nematic phases, while those with a long alkoxy chain exhibit only the nematic phase.     

Nematogenic and smectogenic liquid crystals from new heterocyclic isoflavone derivatives:Synthesis,characterization and X-ray diffraction studies

A new series of liquid crystals comprising eight heterocyclic isoflavone esters,7-alkanoyloxy-3-[4’-(3-methylbutyloxyphenyl)]- 4H-1-benzopyran-4-ones exhibiting enantiotropic nematic(N) and smectic C(SmC) phases were synthesized and investigated.The mesomorphic properties of all derivatives were investigated by means of differential calorimetry and polarized optical microscopy. Wide angle X-ray diffraction technique was employed to investigate the molecular packing associated with the intermolecular interaction as well as the correlation between the thermal behaviour of these compounds with their anisotropy properties within a mesophase.     

Laterally 4-nitrobenzyloxycarbonyl substituted phenyl benzoates: The first two-ring mesogens with a lateral branch containing a phenyl ring

The synthesis and properties of laterally 4-nitrobenzyloxycarbonyl substituted phenyl benzoates are described; these compounds represent the first two-ring mesogens having a phenyl ring in the lateral branch. The lengths of the terminal chains of the core carrying the branch have a great influence, as shown by the phase behaviour of two homologous series. Compounds having long alkyloxy groups exhibit enantiotropic smectic A phases. It should be emphasized that the mesophase thermal stability of these strongly branched derivatives can be higher than that of the laterally unsubstituted parent compound. Connecting two of the new mesogens by means of an aliphatic spacer results in a novel type of twin molecule.     

Laterally 4-nitrobenzyloxycarbonyl substituted phenyl benzoates: The first two-ring mesogens with a lateral branch containing a phenyl ring

The synthesis and properties of laterally 4-nitrobenzyloxycarbonyl substituted phenyl benzoates are described; these compounds represent the first two-ring mesogens having a phenyl ring in the lateral branch. The lengths of the terminal chains of the core carrying the branch have a great influence, as shown by the phase behaviour of two homologous series. Compounds having long alkyloxy groups exhibit enantiotropic smectic A phases. It should be emphasized that the mesophase thermal stability of these strongly branched derivatives can be higher than that of the laterally unsubstituted parent compound. Connecting two of the new mesogens by means of an aliphatic spacer results in a novel type of twin molecule.     

Novel chiral liquid crystals based on amides and azo compounds derived from 2-amino-1,3,4-thiadiazoles: synthesis and mesomorphic properties

Novel chiral amides (Ia-Ie, II) and azo compounds (III, IV) with a 1,3,4-thiadiazole unit in the rigid core were synthesized and their liquid crystalline properties investigated by polarizing optical microscopy and differential scanning calorimetry. The amides Ia-Ie contain a chiral alkoxy chain derived from (R)-2-octanol and an achiral chain varying from 6 to 10 carbon atoms at the end of the rigid core. In amide II one of the terminal group is a chiral alkoxy chain derived from (S)-isoleucine and the other terminal substituent is an achiral n-decyloxy chain. Azo compounds III and IV contain an achiral n-decyloxy chain and a chiral alkoxy chain derived from (R)-2-octanol and (S)-isoleucine, respectively, at the end of the rigid core. The first homologue in the series of amides (Ia) exhibits enantiotropic smectic X (SmX)-chiral nematic (N*) dimorphism and the homologues Ib-Ie display enantiotropic SmX-chiral smectic C (SmC*)-N* mesomorphism. Amide II displays an enantiotropic smectic A phase. The azo compounds III and IV do not show smectic order and only an enantiotropic N* phase was observed. Thus, the mesomorphic behaviour depends on the nature of the central linkage and on the nature of the chiral alkoxy chain.     

U-Shaped dimeric liquid crystals derived from phthalic acid

Details of the transitional properties of four homologous series of U-shaped liquid crystal materials, the benzene-1,2-di-(4-carboxyalkoxybenzylidene-4-n-alkylanilines), are presented. The spacers incorporate 3 to 6 methylene units, whilst terminal aliphatic chain lengths are varied from 1 to 12 units. Members of the two homologous series with an odd number of methylene units in the spacer form nematic and smectic phases as a function of terminal chain length. Materials with an even number of methylene units in the spacer are purely smectogenic, and in both series the first two homologues form only smectic B phases. For all four series the higher homologues show the phase sequence SF/I-SC-SA-I. X-ray diffraction studies have shown that these smectic phases are composed of molecules arranged in bilayers.