Search

In this article, we designed and synthesized two novel swallow-tailed liquid crystal monomers (M1 and M2) with different chain lengths and rigidities centered on 3,4,5-trihydroxybenzoic acid and two series of side-chain liquid crystals polymers PN1 and PN2. All liquid crystal monomers and polymers were conformed to the molecular designs by FT-IR and NMR. The liquid crystal properties were tested by DSC and POM, and the results showed that M1 and M2 were thermotropic enantiotropic nematic liquid crystals and the side-chain liquid crystal polymers PN1 and PN2 series were typical amorphous liquid crystal polymers. With the increase of monomer content, the glass transition temperatures and clearing points of PN1 and PN2 series enhanced. With the increase of the number of mesogens in the liquid crystal monomer, the rigidity was enhanced, and the liquid crystal performance of the polymer was better. [ABSTRACT FROM AUTHOR]

In this paper, a series of novel liquid crystal units (ASE-n, n = 4, 6, 8) of azo Schiff bases with sulphonic acid (-SO3H) as terminal substituents and different alkyl chain lengths were designed and synthesised. Nine star-shaped liquid crystal macromolecules with different central groups (ASE-P-n, ASE-T-n, ASE-G-n, n = 4, 6, 8) were synthesised by esterification of three novel azo Schiff base liquid crystal units (ASE-n, n = 4, 6, 8) with phloroglucinol, pentaerythritol and glucose. The structure of the synthesised compounds were analysed by infrared spectroscopy and 1H NMR. The results showed that all the compounds were consistent with the molecular structure design. The properties of liquid crystal such as phase transition temperature and liquid crystal mesophase range were characterised by POM and DSC. The effects of alkyl chain length and branched degree on the properties of liquid crystal were studied. The maximum absorption spectrum of the compound was determined by UV-Vis spectrophotometry. The photoisomerisation reaction of the compound was also studied. Under ultraviolet light (λ = 365 nm) irradiation, the effect of different duration on the cis-absorption percentage of azo (-N=N-) bond in the compound was studied. [ABSTRACT FROM AUTHOR]

In this study, two novel aromatic ester multi-arm liquid crystal monomers M1 and M2 with different terminal substituents centred on 3,4,5-trihydroxybenzoic acid, and a rod-shaped chiral liquid crystal monomer N were designed and synthesised. The synthesised liquid crystal monomers M and N were grafted and copolymerised with polymethylhydrosiloxane (PMHS). The structural characterisation of the synthesised liquid crystal compounds was carried out by FT-IR and 1H-NMR. The mesomorphic properties of the synthesised liquid crystal compounds were characterised by POM and DSC, and the results showed that the multi-arm liquid crystal monomers M1 and M2 are typical enantiotropic nematic liquid crystal compounds and N is typical thermotropic enantiotropic cholesteric liquid crystal. Polymers P1 and P2 are both cholesteric liquid crystal polymers. The glass transition temperatures and liquid crystal isotropic transition temperatures of polymers P1 and P2 series both tend to increase with the increase of multi-arm liquid crystal monomer M. [ABSTRACT FROM AUTHOR]

In this paper, two novel aromatic ester swallow-tailed liquid crystal monomers M1 and M2 and a straight chain cholesteric liquid crystal monomer M3 were designed and synthesised. Two series of liquid crystal polymers, P1 series and P2 series, were graft-copolymerised with M and polymethylhydrosiloxane (PHMS). All the synthesised liquid crystal monomers and polymers were characterised by IR and 1H NMR and confirmed to the predicted molecular structure. The liquid crystal and thermal properties of the synthesised compounds were tested by DSC, POM, TGA and optical rotation. The results show that the monomer M1 is a monotropic nematic liquid crystal, and the Schlieren texture appears during the cooling process. M2 is an enantiotropic nematic liquid crystal with filamentous and schlieren texture. M3 is a thermotropic enantiotropic cholesteric phase with oily streak and focal cone texture. Both polymers P1 and P2 show typical Grand-Jean texture, and with the increase of monomer M3 content, the polymer clearing point temperature Ti increases continuously, the liquid crystal mesophase range widens, and the specific rotation value increases. [ABSTRACT FROM AUTHOR]

In this paper, we designed and synthesised three Schiff base mesogenic units X-YP and six Y-shaped liquid crystal oligomers X-AYP and X-BYP (×= -CH3O, -CH3, -Cl). Molecular structures of the prepared compounds were confirmed via FT-IR, 1H NMR and elemental analysis. The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarised light microscopy (POM). The photochemical properties of Y-shaped liquid crystal oligomers were preliminarily studied by UV-Vis spectrum. The results indicated that X-YP containing OCH3 and Cl substituents exhibited mesophase, while X-YP with CH3 substituent was non-mesogenic. The synthesized Y-shaped liquid crystals X-AYP and X-BYP both had liquid crystal properties and exhibited nematic phase during heating and cooling, which belonged to thermotropic enantiotropic nematic liquid crystals. The polarity of the terminal groups and the number of mesogenic units had a significant effect on the mesophase behaviour of Y-shaped liquid crystals. The absorption intensities of X-AYP and X-BYP in the UV spectra were affected by the terminal substituents. [ABSTRACT FROM AUTHOR]

In this paper, we designed and synthesised two azo liquid crystal monomers (M1 and M2) and a chiral liquid crystal monomer N, followed by side-chain graft copolymerisation with polymethylhydrosiloxane (PMHS) to synthesize comb-like liquid crystalline polymers PN1 and PN2. The structures of all liquid crystal monomers and polymers conform to the molecular designs by FT-IR and 1H NMR. The liquid crystal properties were tested by DSC and POM, and the results showed that M1 and M2 were thermotropic enantiotropic nematic liquid crystals and N was a thermotropic enantiotropic cholesteric liquid crystal. Both the PN1 and PN2 series were amorphous polymers. The PN1 and PN2 series exhibited a typical Grand-jean texture. The glass transition temperature and isotropic temperature of the PN1 and PN2 series decreased first and then increased with the increase of azo monomer M content. And the glass transition temperature and isotropic temperature of the PN1 series were higher than the PN2 series. Both the PN1 and PN2 series had good thermal stability. The mesophase range of the PN1 series was 173.5°C~181.5°C, and the PN2 series was 162.5°C~172.9°C. [ABSTRACT FROM AUTHOR]

Three series of new branched liquid crystal oligomers with 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid as the centre and cholesterol as the chiral group were designed and synthesised (Dn, Fn and Hn, n = 4,6,8). DSC and POM results showed that their liquid crystal phase behaviour was closely related to the number of mesogenic unit and the rigidity and flexibility of the structure. They were all cholesteric liquid crystals. In the same series, as the value of n increased, the mesophase ranges became narrower. When the value of n was the same in different series, as the degree of branching increased, the mesophase ranges became narrower. [ABSTRACT FROM AUTHOR]

Using tartaric acid as the core, six azo H-shaped liquid crystal compounds M1-M6 with different terminal substituents were synthesised. All products were structurally well characterised by elemental analysis, 1HNMR, and FT-IR. The phase behaviours were investigated by means of polarised optical microscopy and differential scanning calorimetry. M1-M6 were thermotropic enantiotropic nematic liquid crystals. They all showed schlieren texture in the process of heating up, and exhibited spherulite texture in the process of cooling down. M1 and M4 whose terminal substitution was nitro had the widest liquid crystal range in the same series of liquid crystal compounds, which were 135.1°C and 96.1°C, respectively, under heating cycle and 167.4°C and 112.7°C, respectively, under cooling cycle. The results show that the terminal substituents and flexible chain have important influence on the mesogenic phase and range. With the increase of flexibility, the mesogenic range of liquid crystal compounds becomes smaller when the end groups are the same. And when the flexible chain is the same, the greater the induced and polarised force of the terminal substituents, the better the mesogenic properties of the liquid crystal compounds. [ABSTRACT FROM AUTHOR]

A series of star-shaped liquid crystal (LC), respectively, based on phloroglucinol, pentaerythritol and glucose as cores, rod-shaped molecules (MeOSBAA, MeSBAA and ClSBAA) containing a schiff base as mesogenic mesogen were synthesised. The molecular structures were confirmed by FT-IR and 1H-NMR techniques. The LC textures and thermal phase behaviours were investigated by polarising optical microscopy and differential scanning calorimetry. The results showed that MeOSBAA and ClSBAA were thermally enantiotropic liquid crystals. Three-arm star LC macromolecules X-SBA3E and four-arm star LC macromolecules X-SBA4E were found to display enantiotropic nematic liquid crystals behaviour. While the five-arm star-shaped chiral LC molecules X-SBA5E exhibited enantiotropic chiral nematic phase. [ABSTRACT FROM AUTHOR]

This paper designed and synthesised a series of V-shaped liquid crystal molecules (X-SBAnE) with resorcinol as the core and Schiff base as the mesogenic arms (X-SBAAn). The effects of polarity of terminal groups (X=-CH3O,-CH3,-Cl) and length of flexible chain (n = 4,6,8) on mesogenic ranges were discussed. The chemical structure of X-SBAAn and X-SBAnE was studied using FT-IR and 1H-NMR while their thermal behaviour and mesogenic ranges were investigated via differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The results indicated that X-SBAAn containing OCH3 and Cl substituents exhibited mesophase except for the analogue having CH3 substituent which was found to be non-mesogenic. All of the synthesised X-SBAnE had liquid crystal properties and exhibited nematic phases in heating and cooling. The length of the flexible spacers and terminal groups significantly influenced their mesogenic ranges. [ABSTRACT FROM AUTHOR]

Two series of novel four-arm azobenzene liquid crystal molecules were designed and synthesized, and their mesophase properties, photo-induced transition were studied. Two series of mesogenic arms were screened with different length of flexible chain (the carbon number n of flexible chain is 4, 6, 8, 10) using methoxy and nitro as terminal substituents R. The four-arm azobenzene LCs were synthesized by introducing the mesogenic arms into cholic acid. FACAE-O-n, FACAE-N-n all belonged to photosensitive thermotropic enantiotropicnematic LCs. For methoxyl series, melting transitions (Tm), liquid crystal-isotropic transitions (Ti) and mesogenic ranges decreased with the increase of carbon numbers in flexible chain both on heating and cooling. The mesophase performance of FACAE-O-4 was the most excellent. For nitro series, Tm and Ti on heating and cooling decreased with the increase of carbon numbers. Nevertheless, mesogenic ranges increased with the increase of carbon numbers only on heating. The cooling mesogenic ranges showed a trend of rising firstly and then falling, reaching the maximum 103.1oC (n=8). Under ultraviolet irradiation, there was no red shift. The intensity of maximum absorption has changed with the increase of ultraviolet irradiation time. After photo-induced, Tm and Ti on heating and cooling of the four-arm LCs decreased, and the mesogenic ranges became shorter. [ABSTRACT FROM AUTHOR]

Four new liquid crystalline thiophene compounds (M1−M4) with a long flexible spacer were prepared. Their structures were characterized by Fourier transform infrared and proton nuclear magnetic resonance. The mesomorphism and thermal stability were investigated with differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The photo-physical properties were evaluated using ultraviolet/visible spectroscopy and photoluminescence.M1−M4all showed thermotropic mesogenic properties with excellent thermal stability, and exhibited nematic threaded texture, droplet texture, and Schlieren texture on heating and cooling cycles. The effect of flexible spacer and terminal groups on mesomorphic and spectroscopic property is discussed. The experimental results demonstrated that the tendency toward melting temperature (Tm) decreased, while isotropic temperature (Ti) increased with increasing the flexible spacer length. In CHCl3solution, these thiophene compounds displayed an intense broad absorption band peaking within 230–340 nm and a maximum fluorescent emission wavelength at 426–439 nm. [ABSTRACT FROM AUTHOR]

• Three novel unreported mesogens were designed and synthesized, in which the azo and Schiff base were conjugated. • Three series of novel branched azo-Schiff base liquid crystal oligomers were designed and synthesized. • 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid as the center and cholesterol as the chiral group. • The mesomorphic properties change regularly with the branching degree and rigidity and flexibility of the liquid crystal macromolecules. Three novel azo-Schiff base mesogens with different alkyl chain lengths and three series of novel branched liquid crystal oligomers with 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid as the center and cholesterol as the chiral group were designed and synthesized. The test results showed that their liquid crystal phase behavior was closely related to the number of mesogenic units and the rigidity and flexibility of the structure. In the same series, as the value of n increased, the mesophase ranges were widened. When the value of n was the same in different series, as the degree of branching increased, the mesophase ranges were widened. [Display omitted] [ABSTRACT FROM AUTHOR]