Phase behaviour of three homologues of the discotic hexa-n-alkoxyanthraquinones under pressure

The phase transition behaviour of three homologous discotic mesogens, the hexa-n-alkoxyanthraquinones HOAQ(n), n indicating the number of carbon atoms in the alkoxy group, was investigated under hydrostatic pressures up to 500 MPa using a high pressure differential thermal analyser. The T vs. P phase diagrams of HOAQ(6), HOAQ(8) and HOAQ(9) were constructed for solution- (Cr₀) and melt-crystallized (Cr₁) samples of the compounds. HOAQ(6) shows the reversible Cr₀-rectangular columnar phase (Col_r)-hexagonal columnar phase (Col_h)-isotropic liquid (I) phase sequence at atmospheric pressure. The stable Col_r phase of HOAQ(6) has a decreased temperature range with increasing pressure and then the Col_r phase disappears under pressures above about 350 MPa; instead the Cr₀-Col_h-I phase sequence is exhibited. For HOAQ(8), the solution-grown sample exhibits the stable Cr₀-Col_h-I phase sequence at atmospheric pressure. Applying pressure to the solution-grown sample induces the formation of the stable Col_r phase in the pressure region between 10 and 350 MPa, leading to the Cr₀-Col_r-Col_h-I phase sequence. The pressure-induced Col_r phase disappears under higher pressures. The melt-cooled sample of HOAQ(8) shows the formation of the metastable crystal (Cr₁), unknown mesophase (X) and Col_r phases at lower temperatures under atmospheric pressure, and exhibits the reversible Cr₁-X-Col_r-Col_h-I phase sequence on subsequent thermal cycles. The metastable phase sequence was observed under pressures up to 100 MPa, but the phase transitions were too small to be detected under higher pressures. In HOAQ(9) the stable Cr₀-Col_h-I phase sequence is observed at all pressures, while the melt-cooled sample shows the metastable Cr₁-Col_r-Col_h-I phase sequence under pressures up to 300 MPa. The metastable Col_r phase disappears under higher pressures.     

Synthesis and characterization of smectic polymesomorphism in higher homologues of nO.m compounds

Some of the higher homologues of the N-(p-n-alkoxybenzylidene)p-n-alkylanilines, n O.m, compounds with n ≧ 8 and m ≧ 5 have been synthesized and the smectic polymesomorphism studied. The transition temperatures were obtained from both thermal microscopy and differential scanning calorimetry. These compounds in the n O.m series exhibit the usual phase sequences, viz. S_AS_CS_BS_G, and S_AS_BS_G apart from S_AS_CS_FS_G by 9O.8 (and some higher n O.m, like 9O.6). These phases were confirmed by miscibility studies with standard materials. The smectic F phase in 9O.8 compound is also confirmed by an X-ray diffraction study.     

The mesophases of octa-alkanoyloxy-9,10-anthraquinone

Abstract

Nine members of the octa-n-alkanoyloxy-9,10-anthraquinone series, ranging from octanoyloxy (n = 8) to hexadecanoyloxy (n = 16) (where n is the number of carbon atoms per chain), were prepared and their mesomorphic properties studied by differential scanning calorimetry and optical microscopy. All the compounds studied are mesomorphic with the higher homologues exhibiting two (for n ≧ 12) or even three (for n ≧ 14) columnar mesophases. For n = 8 to 11, the phase sequence is C-D_B-I, where D_B is an optically biaxial mesophase with a two-dimensional pgg symmetry. For n = 12, 13, the phase sequence is C-M₃-D_B-I, where M₃ is a highly ordered phase whose structure has not been identified. Finally for n = 14 to 16, the phase sequence is C-M₃-D_B-D_A-I, where D_A is an hexagonal phase. In all cases, the phases change from high to low order with increasing temperature and all transitions are first order. Compared with the corresponding hexa-substituted naphthoquinones the present series generates larger mesomorphic ranges and the higher homologues exhibit a uniaxial phase which is lacking in the hexa-substituted series. The increase in volume occupied by the aliphatic chains in the octa-substituted series is evidently sufficient to reduce the interaction between the aromatic cores of the different columns to permit the stability of a uniaxial phase.     

Transition metals complexed to ordered mesophases. XIII. Synthesis and mesomorphic properties of potentially ferroelectric Schiff's base palladium(II) complexes

A series of N-[4'-(dodecyloxy)resorcylidene]-4-(RO*)-anilines (HL_n n = 1, R*O = (-)-cis-myrtanyl; n = 2, R*O = (-)-menthyl; n = 3, R*O = S-(-)-β-citronellyl; n = 4, R*O = R-(-)-2-octyl) has been synthesized and the mesomorphic properties investigated. These ligands are able to chelate a metal atom; accordingly three different series of palladium complexes, [(Ln)Pd(Ln)], [(Ln)Pd(Azoxy-6)] and [(L₃)Pd(Ph-Py_n)] (where Azoxy-6 and PhPy_n are cyclopalladated 4,4'-dihexyloxyazoxybenzene and 5-substituted-2-(4-substituted-phenyl)pyrimidine, respectively) have been prepared. The mesogenic HL₃ and HL₄ ligands exhibit a S*_C phase, retained in [(L₃)Pd(L₃)], which changes to a cholesteric phase in [(L₄)Pd(L₄)] and becomes the more ordered S*_H phase in the [(Ln)Pd(Azoxy-6)] (n = 3,4) derivatives. In contrast, in the [(L₃)Pd(Ph-Py_n)] compounds the mesomorphic phase is a S_A phase.     

Synthesis and mesomorphic properties of 6-n-decyloxy-2-[4'-N-alkoxyphenylimino)methyl]quinolines (IV)

The synthesis and mesomorphic properties of a new series of liquid crystals derived from quinoline with an imine central bond is described. All compounds exhibit mesophase ranges greater than 50°C. The lower homologues (n = 4-6) show trimorphism S_c-S_a-N (for n = 4, the S_c phase is monotropic). The higher homologues (n = 7-10) show nematic and smectic C phases. Compared to the styrylquinoline analogues the imine bond gives rise to similar liquid crystal phase ranges but lower melting points.     

Density and refractive index measurements in hexaheptyloxytriphenylene, a discotic liquid crystal

Density and refractive index measurements in the discotic liquid crystal hexaheptyloxytriphenylene were performed in the hexagonal columnar Col_ho and isotropic I phases. The temperature dependence of the density ρ(T) for this compound was obtained by combining small angle X-ray data and capillary methods. The ordinary n_o extraordinary n_e and isotropic liquid n_i refractive indices were measured using a modified Abbe refractometer to an accuracy of about 10^-3. To check the consistency of the density and the refractometry experiments we used the Lorentz-Lorenz relation. An anomaly in the empirical relationship at the Col_ho-I phase transition, which holds for many uniaxial liquid crystals, was detected. A discrepancy between low birefringence Δn∼0.109 and a relatively high local electric field anisotropy for hexaheptyloxytriphenylene is discussed.     

Structural characterization of the smectic polymorphism of chiral liquid crystalline polysiloxanes containing biphenyl mesogens

A structural characterization of chiral side chain siloxanes with different average degrees of polymerization, DP_n, was performed by X-ray diffraction experiments on powder and oriented fibre specimens. Polymers (DP_n = 35) and oligomers (DP_n = 4) contained the 4,4'-biphenylene unit with either an (S)-2-methylbutoxy (An, Bn) or an (S)-2-chloro-3-methylbutanoyloxy substituent (Cll). The spacer segment connected to the siloxane backbone had a variable number, n, of methylene groups (n = 5, 8, or 11). Independent of the spacer length and the chiral tail nature, the polysiloxanes underwent the same sequence of phases: C-S_F1 (or S_I1)-S_C1-S_A1-I, whereas in the oligosiloxanes the sequence C-S_B1-S_A1-I (B11) or C-S_F1-S_C1-I (B5) occurred. The influence of the structure of the polysiloxanes on the formation of the smectic (tilted or orthogonal) mesophases was elucidated. The rather large number of reflections (three or four) detected in the X-ray patterns at low angles, allowed a drawing of the projection of the electron density profiles along the layer normal, p(z), and deduction of the most physically acceptable electron density profiles from among the numerous possibilities for each smectic phase. The electron density profiles were in agreement with monolayer smectic phases presenting a microphase separation between the siloxane backbones and the side chains, so constraining the polymer backbones within a thin layer.     

The N,N'-bis[4-(4-n-alkyloxybenzoyloxy)benzylidene]phenylene-1,3-diamines: mesophase behaviour and physical properties

A homologous series of banana-shaped compounds (n =1-12) is described. The short-chain derivatives exhibit a B₆ phase, while B₆/B₁ dimorphism is found for the pentyloxy and hexyloxy homologues. The B₁ phase of the compounds having longer alkyloxy chains is changed to a B₂ phase for the compounds with n =11 and 12. The phase characterization was performed using their optical textures and by means of X-ray investigations. Transition enthalpies were measured using DSC. In addition, density measurements were performed on one selected homologue. The compound n =8 exhibiting a B₁ phase was investigated also by high-pressure DTA.     

Synthesis and characterization of new ferroelectric liquid crystals containing a phenyl biphenyl carboxylate mesogenic group and oligooxyethylene spacers

Two series of ferroelectric liquid crystals containing a phenyl biphenyl carboxylate mesogenic group and oligooxyethylene spacers were synthesized. The mesomorphic behaviours of the compounds were characterized using differential scanning calorimetry (DSC), optical polarizing microscopy (POM) and powder X-ray diffraction measurements. These series all contain a smectic A (S_A), a chiral smectic C (S_C) and a crystal E (C_r E) phase sequence. The ordered smectic Cr E phase was observed for the short spacer chain (n = 0, 1, 2) homologues of the two series. Moreover, the mesomorphic properties are discussed as a function of the oligooxyethylene spacer length, and the position of the aromatic core rings. These results indicate that the structures with a rigid part (biphenyl group) closer to the flexible spacer chain (oxyethylene unit) tend to form the symmetrical smectic S_A and Cr E phases.     

High speed parallel synthesis of banana-shaped molecules and phase transition behaviour of 4-bromo-substituted derivatives

Novel derivative series of the well known bent-shaped P-n-O-PIMB liquid crystal mesogens, referred to as '4Br-P-n-O-PIMB', '4Cl-P-n-O-PIMB' and '5Cl-P-n-O-PIMB', having halogen atoms substituted on the phenyl ring in the central core, were synthesized by solution phase parallel synthesis based on a combinatorial approach. The mesomorphic behaviour and physical properties of all the new compounds were studied by means of optical microscopy, differential scanning calorimetry, X-ray and circular dichroism spectroscopy. We found interesting transitional behaviour for the 4Br-P-n-O-PIMB homologous series. The homologues with alkyl tails having carbon numbers of n=3-10, 12, 14 exhibit rather complicated mesomorphic behaviour, which is strongly sensitive to n. The chiral fluid smectic B2 phase with SmC_AP_A structure and unidentified smectic Bx phase were observed in the homologues with n=9, 10, 12, 14 and n=3-5, respectively. Interestingly, every member exhibits frustrated and/or helical ordered phases at low temperatures, designated as X1, X2, and X3 phases, which result from a spontaneous escape from a macroscopic polarization. The mesomorphic behaviour and mesophase structures differ remarkably from those of the parent P-n-O-PIMB homologues, suggesting that substitution of the halogen atoms at the central core essentially creates a particular interaction between molecules.     

The influence of terminal chlorine on the mesomorphic properties of new thiobenzoates containing two and three benzene rings

New liquid crystalline chloro-substituted thioesters containing two and three benzene rings have been synthesized. 4-Chlorophenyl 4-n-alkoxythiobenzoates and 4-chlorophenyl 4-n-alkoxybenzoyloxy-4'-thiobenzoates are referred to as nO.SCl and nO.OSCl, respectively, where n varies from 4 to 16 for nO.SCl, from 4 to 10 for nO.OSCl and denotes the number of carbon atoms in the alkyl chain. Their mesomorphic properties were investigated by means of polarizing optical microscopy, differential scanning calorimetry, transmittance light intensity and X-ray diffraction measurements. The nO.SCl homologous series possesses smectic A (SmA) and nematic (N) phases for n = 4, 5, 6 while higher homologues have only an enantiotropic SmA phase. Those from the nO.OSCl homologous series have enantiotropic N and SmA phases and higher transition temperatures. The range of the N phase decreases, and of the SmA increases, with the elongation of the alkoxy chain in the nO.OSCl homologous series. The effect on mesomorphic behaviour of terminal alkoxy chain lengthening and replacement by chlorine on the other side of the molecule is discussed.     

Synthesis and thermal properties of mesomorphic 1,1'-bis[ω-(4'-cyano-4-biphenyloxy)alkyl] ferrocenes

A new series of 1,1'-disubstituted ferrocene compounds of the type [(η⁵-C₅H₄(CH₂)_nOC₆H₄C₆H₄CN]₂Fe (3a-d, n = 5, 6, 8, 11) incorporating a variable length alkyloxy cyanobiphenyl unit has been prepared and their mesomorphic properties have been investigated. Compounds 3b, c and d exhibit a thermotropic smectic C phase and 3c also exhibits a monotropic smectic A phase over a fairly wide range near ambient temperature.     

Synthesis and mesomorphic properties of chiral liquid crystals having thiolactate groups

A homologous series of chiral thiolactate liquid crystals, alkyl 2-[4-(4-decyloxyphenyl)benzoyloxyphenyloxy]thiopropionates, ADBPT-n (n=2-6), was prepared from (R)-2-(4-hydroxyphenoxy)propionic acid. Structural effects on the mesomorphic and physical properties were investigated in terms of variation in the length of alkyl chain attached to the thiolactate group. The mesophases and their corresponding transition temperatures were identified by polarizing optical microscopy and differential scanning calorimetry. Compound ADBPT-4 exhibited SmA* and SmC* phases, whereas other compounds in the series exhibited the SmA* phase along with unidentified SmX₁* and SmX₂* phases. The maximum P_s value measured for ADBPT-4 in the SmC* phase was 17.5 nC cm^-2, suggesting the polarization of the material is rather low. The tilt angles were also measured, reaching a maximum of 48 degree.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures XII. Binary mixtures of homologues of unsymmetrical 1,4-phenylene bis (4-substituted benzoates)

Twentyfour liquid crystalline esters of the type 4-(n-C_nH_2n+1O)C₆H₄COOC₆H₄OOCC₆H₄-X-4 have been investigated for their phase behaviour. These compounds constitute six homologous series that differ from each other by the substituent X. The latter varies between CH₃O, CH₃, Cl, CN, NO₂, and n-C_nH_2n+1O, and the number (n) of carbons varies, within a homologous series, between 6, 8, 14, and 16. All possible binary mixtures made from any two homologues were prepared and characterized for their mesophase behaviour by differential scanning calorimetry and polarizing optical microscopy.     

Discotic liquid crystals of transition metal complexes X. Phthalocyanine derivatives substituted with n-alkyloxyphenyl side chains

Octakis(alkyloxyphenyl)-phthalocyanine derivatives ((C_nOph)₈PcH₂ n = 8, 10 12 and 18), their corresponding copper (II) complexes ((C_nOph)₈PcCu, n = 10, 12 and 18) and octakis(2-ethylhexyl)-PcH₂ have been synthesized and their mesomorphic properties characterized. (C_nOph)₈PcH₂, (n = 12 and 18) exhibit hexagona disordered columnar mesophases whereas (C_nOph)₈PcCu (n = 12 and 18) yields a rectangular disordered columnar liquid crystal. An alkylphenyl-oxymethyl derivative, (C₁₂phOCH₂)₈PcH₂, was synthesized to determine the influence of the connecting link between the side chains and the phthalocyanine macrocycle on the mesomorphic properties.     

Protonation and hydrogenation of triosmium clusters containing the bridging diphosphine ligands Ph2P(CH2nPPh2 (n = 1 to 4)

Members of the series of bridging diphosphine clusters [Os₃(CO)₁₀(diphos)] where diphos = Ph₂P(CH_2nPPh₂ [dppm (n = 1), dppe (n = 2), dppp (n = 3), or dppb (n = 4)] show interesting differences in their reactivity towards H⁺ and H₂. Protonation leads to [Os₃(μ-H)(CO)₁₀(diphos)]⁺ with the hydrides bridging the same osmium atoms as the diphos ligand when diphos is dppe, dppp, or dppb, whereas the hydride and dppm bridge different edges in [Os₃9μ-H)(CO)₁₀(dppm)]⁺. Hydrogenation of the 1,2-diphos compounds leads to [Os₃(μ-H)₂(CO)₈(diphos)] (diphos = dppm, dppe, dppp) in good to excellent yield but the dppb analogue could not be made. Geometric and electronic factors affecting the ability to incorporate hydride ligands in these clusters are discussed.     

Reaction between cerium trifluoride and elemental fluorine

Reactions between cerium trifluoride and elemental fluorine have been examined by means of the kinetic and crystallographic method. The reactions were performed at 503–573 K under fluorine pressures of 6.7–26.7 kPa for reaction time up to 3 h. Two kinds of CeF₄ were synthesized by controlling the reaction condition. One is the metastable CeF₄-I synthesized at 523–538 K which returns to CeF₃ to release elemental fluorine, and the other is the stable CeF₄-II obtained at temperatures higher than ca. 540 K, which never returns to CeF₃. X-ray diffraction–Rietveld analysis revealed that the structure of CeF₄-I and CeF₄-II were monoclinic structure (C12/c1, Z=12, CeF₄-I/CeF₄-II: a₀, 1.26 nm/1.25; b₀, 1.06/1.05; c₀, 0.82/0.82; β, 126.1/126.3°; cell volume, 8.91×10⁻²⁸/8.78×10⁻²⁸ m³) and the cell volume of the CeF₄-I was 1.4% larger than that of the CeF₄-II. Bond lengths between Ce and F in CeF₄-I were somewhat longer than those in CeF₄-II. When CeF₄ and NaCl were put separately in the reaction container, CeF₄-I changed to CeF₃ with converting NaCl to NaF, however, CeF₄-II never reacted with NaCl.     

The synthesis and liquid crystalline behaviour of 2-(4-n-alkoxyphenyl)-5-methylpyridines

We have synthesized a new series of polyphenylene compounds with a pyridine ring, 2-(4-n-alkoxyphenyl)-5-methylpyridines (CH₃C₅H₃NC₆H₄OC_iH_2i1) (1a-i; the carbon number, i, of the alkoxy group is 1-9), and studied their phase transitions and mesogenicity using DSC and polarizing microscopy. In the homologous series of 1a-i, no mesomorphic phase appeared for i=1-5 and only a monotropic nematic phase was observed for i=6-9. The mesomorphic potential is relatively weaker for the 1a-i than for the 2a-i and 3a-i homologues, which are pyridine-containing three- and four-ring similar systems. This lowering of the mesogenicity may be due to the lack of a phenyl ring between the pyridine ring and the methyl group in the 1a-i homologues.     

Mixed-valent diruthenium (II,III) aliphatic carboxylates: columnar mesophases in dodecylsulfate and octylsulfonate derivatives

Two series of polymeric mixed-valent diruthenium (II,III) aliphatic carboxylates of formula Ru₂[O₂C(CH₂)_n-2CH₃]₄X (where X=dodecylsulfate (DOS) anion and n=8, 9, 16 and 18, or X=octylsulfonate (OS) anion and n=8, 10, 12, 14 and 18) were synthesized and characterized. Their liquid crystalline properties and crystalline (Cr) structures were analysed; the Cr phases are lamellar in all cases. For long chain DOS derivatives (n=16 and 18) hexagonal and rectangular columnar mesophases (Col_h and Col_r) with melting temperatures close to 140°C were observed. For long chain OS derivatives (n≥10) a Col_h mesophase was observed, with melting temperatures between 140 and 190°C.     

Transition metal complexes with long-chain amines thermal behaviour and crystal structure of (n-CaH2a+1NH2)2ZnCl2

The thermal behaviour of (n-C_aH_2n+1NH₂)₂ZnCl₂ complexes with n = 6, 8, … 16 has been investigated by DSC and by temperature variable IR and X-ray powder diffraction techniques. Complexes with n = 12,14,16 show solid—solid phase transition which are “melting” transitions of the hydrocarbon regions of the structure. The crystal structure of both the low and the high temperature polymorphs is characterized by the piling of sandwiches, each formed by an “inorganic” layer sandwiched between two alkylammonium layers.