A systematic study on the influences of linkage length on phase behaviours and charge carrier mobilities of discotic dimers

Two series of discotic dimers T3Dn and T5Dn based on hexapropoxytriphenylene (HAT3) and hexapentyloxytriphenylene(HAT5), respectively, with polymethylene linkage O(CH₂)_nO (n = 3–12) have been synthesised. Their mesomorphism was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results showed that side chains induced a phase transition from col_hp phase to col_h phase, namely dimers T3Dn (n = 6–12) based on HAT3 exhibiting a single col_hp phase, dimers T4Dn (n = 6, 7, 11, 12) based on HAT4 showing a highly ordered col_hp phase in low-temperature region and a col_h phase in high-temperature region, dimers T4Dn (n = 8–10) based on HAT4 displaying a single col_hp phase and dimers T5Dn (n = 6–11) based on HAT5 indicating a single col_h phase. Dimers T4Dn showed a phase competition between col_h phase and col_hp phase induced by linkages. Surprisingly, a unique phenomenon was found by us, that is, those compounds in which linkage lengths were twice those of side chains showed the largest enthalpies, the smallest intracolumnar spacings and the highest charge-carrier mobilities among their homologues, respectively, which implied that they formed the most highly ordered phase among their homologues.     

‘Thermodynamic,structural and morphological studies on liquid-crystalline blue phases’ by H. Stegemeyer,Th. Blümel,K. Hiltrop,H. Onusseit and F. Porsch

Abstract

In the review article on cholesteric blue phases by Stegemeyer et al. [1], table 3 lists [100] as the second largest BPI facet and the largest BPII facet. If such is the case, then, it is important to realize that it is unlikely the body centred cubic phase of BPI has O⁸(I4 ₁32) symmetry and the simple cubic phase of BPII, O²(P4₂32) symmetry [2–4].     

New chiral liquid crystal cyclic monomers based on diosgenin: synthesis and mesomorphism

A series of new chiral liquid crystal (LC) intermediate compounds (LC-C₁~LC-C₄) containing diosgenyl groups and the corresponding cyclic LC aliphatic carbonate monomers (LC-M₁~LC-M₄) were synthesised to investigate the relationship between their structures and phase behaviour. The chemical structures of the compounds obtained in this study were characterised using FT-IR, ¹H NMR and ¹³C NMR measurement. The phase behaviour and mesophase structure were investigated with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurement. As a result, LC-C₁ and LC-C₂ showed focal conic texture of the choleteric phase, while LC-C₃ and LC-C₄ with longer spacer length showed fan-shaped texture of a smectic A phase. The monomers (LC-M₁~LC-M₄) all exhibited focal conic texture of the choleteric phase on heating and cooling cycles. Furthermore, the effect of the spacer length on phase behaviour of the LC compounds was discussed.     

Effect of the lanthanoid-size on the structure of a series of lanthanoid-anilato 2-D lattices*

Abstract

We report the synthesis and characterization of a series of Ln-based bromoanilato 2-D lattices with dimethyl sulfoxide (DMSO): [Ln₂(C₆O₄Br₂)₃(DMSO)_n]·2DMSO·mH₂O with n = 6 and m = 0 for Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6) and Gd (7); n = 4 and m = 2 for Ln = Tb (8), Dy (9), Ho (10), Er (11), Tm (12) and Yb (13) (C₆O₄Br₂^2? = 3,6-dibromo-2,5-dihydroxy-1,4-benzoquinone = bromoanilato). The X-ray analysis shows that the largest Ln(III) ions (La-Gd, 1-7) crystallize in the monoclinic P21/n space group (phase I), whereas the smaller Ln(III) ions (Tb–Yb, 8–13) crystallize in the triclinic P-1 space group (phase II). Both phases present a (6,3)-2-D topology but show important differences derived from the different coordination number of the Ln(III) in both phases. In phase I, the Ln(III) ions are nine-coordinate with a tri-capped trigonal prism geometry and rectangular cavities with no solvent molecules. In phase II, the Ln(III) ions are eight-coordinate with a triangular dodecahedral geometry and distorted hexagonal cavities having two water molecules. These differences are due to the lanthanoid contraction. The magnetic properties show that the Ln(III) ions are isolated and do not present any noticeable magnetic interactions as expected for bromoanilato bridges and Ln(III) ions.     

The effect of mesogenic and non-mesogenic crosslinking units on the phase behaviour of side-chain smectic and cholesteric elastomers

Chiral monomer (M₁ ), mesogenic and non-mesogenic crosslinking agents (C₁ and C₂ ), and the corresponding liquid crystalline elastomers (P₁ and P₂ series), have been synthesised. Their chemical structures have been characterised by Fourier transform infrared or ¹H nuclear magnetic resonance and their phase behaviour investigated by differential scanning calorimetry, polarising optical miscoscopy, thermo-gravimetric analysis (TGA) and X-ray diffraction. The effect of the crosslinking unit on the phase behaviour of the elastomers has been studied. M₁ showed a cholesteric oily streak and focal conic texture. C₂ exhibited a nematic enantiotropic thread-like and schlieren texture, and a monotropic fan-shaped texture in the S_A phase. Due to the introduction of the mesogenic crosslinking unit, elastomers, P_2-1 ?P_2-5 , exhibited a cholesteric phase, while elastomers, P_1-1 ?P_1-4 , derived from a non-mesogenic crosslinking unit, exhibit a S_A phase. As the content of the crosslinking unit increased, the T _g of the P₁ series initially decreased and then increased, and the T _i of the series decreased. In the P₂ series the T _g increased, but the T _i initially increased and then decreased. TGA confirmed that all the elastomers had improved thermal stability.     

The substituent effect on mesomorphic properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates

Abstract

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the S_A phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the S_A phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the S_A-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.     

Peculiarities of thermal decomposition of inorganic and organometallic compounds of GeIV and GeII. Thermolysis of (acac)2GeX2 (X = Cl,N3) and (CO)5MGeCl2(thf) (M = Cr,Mo, W)

Thermal decomposition of the complexes (acac)₂Ge(N₃)₂ (1), (acac)₂GeCl₂ (2), and (CO)₅M=GeCl₂(THF) (M = Cr (3), Mo (4), W (5)) was studied by differential scanning calorimetry and thermogravimetry. The phase compositions of the products of thermolysis of compounds 1—3 and 5 were determined by X-ray phase analysis. Possible schemes of thermal decomposition of these compounds were proposed. The heat capacities of complexes 3—5 were studied in the temperature range 113—313 K. The structures of complexes 1 and 5 were established by X-ray diffraction analysis.     

207Pb N.M.R. of lead(II) soaps in solid,liquid-crystalline and liquid phases

Abstract

²⁰⁷Pb N.M.R. data are reported for a number of even chain length lead(II) carboxylates (soaps) at various temperatures. At room temperature, the solid lead(II) decanoate and tetradecanoate show similar spectra, with a single metal ion site, and modest shielding anisotropy. As the temperature is increased, the soaps (hexanoate to octadecanoate) all form a highly ordered smectic phase, which gives a very broad ²⁰⁷Pb signal of linewidth comparable to that of the solid phase. At higher temperatures, the hexanoate to dodecanoate soaps form a lamellar L _α (smectic A) phase, whilst the longer chain length carboxylates melt directly to the liquid phase. Both the lamellar L _α and liquid phase give fairly sharp, isotropic signals, whose chemical shifts and linewidths are strongly temperature dependent. Possible explanations for this effect include paramagnetic contributions to the shielding tensor from low-lying electronic states of Pb(II), and contributions to the observed signal from different coordination species produced in the lead(II) carboxylate system. Although there are discrete changes in chemical shift at the phase transition, the magnitudes observed in all the phases are similar, suggesting that there are no dramatic changes in the metal coordination environment.     

Obituary: Professor Frank M. Leslie FRS (1935-2000)

The synthesis of five new cholesteryl-based monomers (M-1?M-5) and the corresponding smectic comb-like polymers containing cholesteryl groups (P-1?P-5) is presented. The chemical structures were characterised by FT-IR, 1H NMR and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The phase behaviour was investigated by polarising optical microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction. The specific optical rotation values of these monomers and polymers with the same number of phenyl rings and terminal groups were nearly equal; however, they decreased with increasing the aryl numbers in the mesogenic core. The monomers M-1?M-5 showed oily streak and focal conic optical textures, or finger print textures characteristic of the chiral nematic phase. The polymers P-1?P-5 showed the smectic A phase. The melting, clearing, and glass transition temperatures increased, and the mesophase temperature ranges widened with increasing the aryl number in the mesogenic core. However, although the molecular structures of M-4 and M-5 were similar to those of M-3, namely their mesogenic cores contained three phenyl rings, their phase behaviour differed considerably, and T _m and T _i of M-4 and M-5 were less than those of M-3. In addition, M-4 and M-5 showed a clear glass transition similar to the polymer. Furthermore, the ester linkage bond and aryl arrangement in the mesogenic core also affected the phase behaviour.     

V-shaped switching in binary mixtures of an achiral swallow-tailed material with the antiferroelectric liquid crystal (S)-MHPOBC

An achiral swallow-tailed material, 2-propylpentyl 4-(4′-decyloxybiphenyl-4-carbonyloxy)benzoate, p, showing SmA and SmC_alt phases was prepared for mixing (by weight percentage) with an antiferroelectric liquid crystal, (S)-MHPOBC, m, for the study. The binary mixture p/15/m85 using (S)-MHPOBC (85%) as a host doped with achiral material (15%) resulted in a phase sequence SmA-SmC*-SmC*_A. The electro-optic response of this mixture in the ferroelectric SmC* phase displayed V-shaped switching, while that in the antiferroelectric SmC*_A phase displayed a double hysteresis switching. The mixture p85/m15 possessed SmA* and SmC*_A phases; V-shaped switching was found in the antiferroelectric SmC*_A phase of this mixture. These optical phenomena implied that a binary mixture containing a larger amount of achiral swallow-tailed material and/or possessing relatively lower polarization favours the occurrence of V-shaped switching in the antiferroelectric phase. The results of this work also suggested that thresholdless V-shaped switching in chiral smectic liquid crystals can be achieved by mixing an achiral swallow-tailed material with an antiferroelectric liquid crystal.     

Novel supramolecular columnar liquid crystals based on thiosemicarbazides

Novel liquid crystal materials based on 3,4-di-n-alkoxybenzoylthiosemicarbazides (3a–h, n = 5–10, 12, 14) were synthesised. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. Compound 3a did not show mesomorphic properties; 3b shows a monotropic hexagonal columnar (Col_h) phase. Compounds 3c–h display an enantiotropic Col_h phase. The mesomorphic properties were found to be dependent on the length of alkoxy side chains. In N,N-dimethylformamide solution, all the compounds displayed a room temperature emission with λ_max at 361–332 nm. A thermogravimetric analysis also was performed.     

The effect of different arms on the properties of chiral branched-arm liquid crystals based on isosorbide as the chiral core

A new series of two-arm ( MA₁ , MA₂ ), four-arm ( MA₃ ) and six-arm ( MA₄ ) chiral liquid crystalline compounds containing isosorbide as the chiral core were synthesised. Four precursors of branched-arm A₁–A₄ were first obtained, and then were esterised separately with isosorbide to obtain four chiral branched-arm liquid crystals ( MA₁–MA₄ ). The structure and properties have been characterised. The results show that MA₁ was smectic–cholesteric phase with a fan-like and oily streak texture; MA₂–MA₄ showed a cholesteric phase with oily streak texture, or lined texture and finger print texture. Isosorbide successfully induced a cholesteric phase. The melting point and clearing point values for MA₁–MA₄ first increased and then decreased. The branched-arm and chiral core quantity affected the liquid crystalline properties. At the same time, the difference in side-arms resulted in different directions of rotation. MA₁–MA₂ showed right-handed rotation and had selective reflection; MA₃–MA₄ demonstrated left-handed rotation and did not have selective reflection.     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

Effect of spacer length on mesomorphic behaviours of chiral liquid crystal compounds containing (-)-menthyl

ABSTRACT

A homologous series of new chiral liquid crystal compounds, MnBEB (n = 4–10), was prepared by covalently linking a chiral (–)-menthyl with biphenyl-benzoate via a dicarboxylic spacer of varying length and parity. A combination of analysis methods, such as FT-IR, ¹H NMR spectra, differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction was carried out to systematically investigate their phase structures and phase transition behaviours. The length and parity of the flexible spacers has a profound influence on the T_m and T_c and a modest odd-even effect is observed for the chiral liquid crystal compounds MnBEB. Only compound M4BEB developed an N* phase with selectively reflection on heating and a blue phase on cooling process. In addition, increasing the length of the flexible spacers tends to narrow the temperature range of the N* phase and widen the smectic phase, moreover, the pitch becomes longer with the spacer increases.     

化学修饰1，4，7，10-四氮杂环十二烷提高铼酸化合物的相变温度

通过碘甲烷对1,4,7,10-四氮杂环十二烷（cyclen）进行化学修饰得到甲基取代的N-甲基-1,4,7,10-四氮杂环十二烷（Me-cyclen）。将cyclen和Me-cyclen与HReO₄以1∶2的比例进行反应,分别获得化合物（cyclen）（ReO₄）₂（1）和（Me-cyclen）（ReO₄）₂（2）。差示扫描量热法和介电研究发现化合物1和2具有可逆的相变,相变温度为324 K （1）和384 K （2）。以上研究表明：通过对环状有机胺进行化学改性,在降低分子对称性同时可以显著提高该有机-无机杂化材料的相变温度。     

Nonaqueous Liquid-Liquid Extraction. Extraction of Zinc from Methanol-Water Solution of Chloride by Trioctylphosph1Ne Oxide in Decaline

Abstract

The distribution of zinc was studied between the decaline phase having tri-n-octylphosphine oxide (TOPO) and the methanol-water phase (4:1 in molar ratio) having chloride ion, and the stability constants of zinc with chloride in the methanolic solution were calculated from the extraction experiments (K₁ = 2.4 × 10³, K₂ = 1.9 × 10²at 298°K).     

Chiral discotic derivatives of 1,3,5-triphenyl-6-oxoverdazyl radical

Two derivatives of 1,3,5-aryl-6-oxoverdazyl containing two 3,4,5-trioctyloxyphenyl and one 3,4,5-tri((S)-3,7-dimethyloctyloxy)phenyl group in position C(3) (1b) or N(1) (1c) were investigated by thermal, X-ray diffraction and magnetic methods. The results were compared to those obtained for achiral derivative 1a containing three 3,4,5-trioctyloxyphenyl groups. All three compounds exhibit an ordered columnar hexagonal phase, Col_h(o), and for chiral derivatives, 1b and 1c, a superstructure with doubled periodicity was found. The introduction of the three chiral alkoxy substituents in 1a lowered the mesophase stability by about 50 K and induced a Col_h phase in 1c. Thermochromic analysis showed a hypsochromic shift upon formation of the Col_h(o) phase similar for all three derivatives 1 (~0.3 eV), which coincides with a 5% drop in effective magnetic moment, μ_eff, for 1c. Analysis of magnetisation data in a range of 2–370 K at 200 Oe revealed weak antiferromagnetic interactions (θ = – 4 K) in the Col_h(o) phase.     

The binary system composed of a bent-core compound forming a B7 phase and a nematogenic calamitic compound

The isobaric phase diagram for a binary system of liquid crystals is presented. One mixing component is a bent-core mesogen forming a B₇ phase and the other one is a nematogenic calamitic compound. The occurring mesophases have been identified by their optical textures as well as by X-ray investigations. The B₇ phase exists down to about 60 mol% of the bent-core compound A / 40 mol% of the calamitic compound B. Two additional mesophases are induced in the mixed phase region. At medium concentrations (around 50 mol%) an oblique columnar phase appears which shows a similar X-ray pattern to the B₇ phase but an utterly different nucleation on cooling the isotropic liquid and a completely dissimilar texture. At concentrations below 35 mol% A, a further phase is induced which possesses an irregularly modulated layer structure. This phase can be regarded as an intermediate state between the regularly modulated Col_r (B₁) phase and the intercalated B₆ phase. It transforms on cooling into the phase with a regularly modulated structure.     

Optical and mesomorphic properties characterisation of chiral liquid crystalline copolysiloxane exhibiting cholesteric and blue phases

A series of liquid crystalline polymers (LCPs) have been synthesised by two cholesteric monomers M₁, M₂ and a nematic monomer M₃. The chemical structures and liquid crystalline properties of the monomers and polymers have been characterised by FTIR, ¹H-NMR, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction measurements and polarising optical microscopy. All LCPs show a high thermal stability with wide mesophase temperature ranges. For polymer P₁ bearing only cholesteric LC monomers component, it shows a cholesteric phase, whereas others display a blue phase besides a cholesteric phase. The formation of the blue phase is based on the structures of the polymers and the produced biaxial helix. The glass transition temperature and isotropic temperature of the polymers decrease on heating cycle with increasing the content of M₃ in the polymers. The specific rotation values of the polymers are temperature-sensitive. The reflection spectra of polymers P₁–P₆ show that the maximum reflected wavelengths shift to long wavelength with increasing the content of M₃ in the polymer systems. The frequency and intensity of the bands change sharply at the temperature where cholesteric phase changes to blue phase, but they show a weak dependence on temperature in the blue phase.     

POLYESTERIMIDE-MODIFIED BISMALEIMIDE RESINS. I. EFFECT OF POLYESTERIMI DE CONTENT

ABSTRACT

A novel polyesterimide (PEsI-M) was used to improve toughness of bismaleimide (BMI) resin composed of bis(4-maleimidediphenyl) methane (BDM) and O,O′-diallyl bisphenol A (DBA). Morphologies of modified resins changed from spherical particles to inverted phase structures, depending on PEsI-M's content based on the observation of scanning electronic microscopy (SEM). PEsI-M was an effective morphology modifier so that loading of 12 pbw resulted in a diverted phase structure. Dynamic mechanical analysis (DMA), rheometrics mechanical spectroscopy (RMS) and differential scanning calorimetry (DSC) were respectively used to investigate the dynamic mechanical behavior, and the gelation time and the curing extent of unmodified and modified BMI resins. The fairly uniform morphology in 15 pbw PEsI-M modified system cured at 180°C suggests that the phase separation might take place via a spinodal decomposition mechanism. The fracture energy (G _IC ) increased with the increase of PEsI-M content in the modified system. G _IC of 15 pbw PEsI-M modified system was 0.63 times larger than that of the unmodified BMI resin.