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

Binary mixtures formed from components of the four series of unsymmetrical 1,4-phenylene bis-4-substituted benzoates, in which one substituent is a terminal alkoxy group with a number of carbon atoms kept constant (at n =6, 8, 14 and 16) while the other substituent (X) ranges through CH₃O, CH₃, Cl, CN and NO₂, were prepared and characterized for their mesophase behaviour. Transition temperatures of the mixtures prepared were measured by differential scanning calorimetry and identified by polarizing optical microscopy. Phase diagrams for the various binary combinations were constructed to investigate the dependence of the phase behaviour of mixed systems upon the electronic nature of the terminal group X, as well as on the chain length of the alkoxy group. The results are discussed in terms of mesomeric and polarizability effects.     

Phase behaviour of binary mixtures of 4-substituted phenyl 4'-n-alkoxybenzoates

Five homologous series Ia-e, of the title compounds have been prepared and investigated for their mesophase behaviour in binary mixtures. Each series differs from the other by a substituent X, which changes between CH₃O, CH₃, Cl, CN, and NO₂. The number of carbons in the terminal alkoxy group, within a homologous series, varies between 6, 8, 14, and 16. All possible binary combinations, made from any two components bearing an alkoxy group of the same chain length but two different substituents X, were prepared and similarly characterized for their phase behaviour. Transition temperatures of the mixtures were measured by differential scanning calorimetry and identified by polarizing optical microscopy. Phase diagrams were constructed for the various binary systems and discussed in terms of electronic effects.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures XIII. 4-(4-Substituted phenylazo)phenyl 4-alkoxybenzoates

Five homologous series of 4-(4-substituted phenylazo)phenyl 4-alkoxybenzoates (Ia-e) were prepared in which the substituent (X) was taken from CH₃O, CH₃, Cl, NO₂, and CN, while, within each homologous series, the length of the terminal alkoxy group varied between 6 and 16 carbon atoms. Compounds prepared were characterized by infrared spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and polarizing optical microscopy. The results are discussed in terms of mesomeric and polarizability effects. In each group of compounds bearing the same alkoxy group, the mesophase - isotropic transition temperatures (T_c) were successfully correlated with the polarizability anisotropy of bonds to the substituent X.     

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.     

Effect of substituents and alkoxy chain length on the phase behaviour and optical properties of 4-substituted-phenyl 4-alkoxybenzoates

The refractive indices as functions of temperature were measured for 4-substituted-phenyl 4-alkoxybenzoates in which one substituent is a terminal alkoxy group with the number of carbon atoms kept constant (at n=6, 8, 14, or 16), while the other terminal substituent was either CH₃O, CH₃, Cl, CN or NO₂. Polarizing optical microscopy was also used to identify mesophases and measure their transition temperatures. The results are discussed in terms of electronic polarizability effects.     

Supercooling phenomena in binary mixtures of acetamide and inorganic salts

Liquid—solid equilibrium temperatures are measured in binary mixtures of acetamide and inorganic salts [NaClO₄, LiCNS, LiNO₃, CH₃COOLi, Ca(NO₃)₂, (CH₃)₄ NCl, (C₂H ₅)₄ NBr]. In some ranges of concentration all these systems (with the exception of CH₃COOLi, R₄NX) exhibit supercooling phenomena and crystallization occurs only through vigorous agitation and in the presence of crystalline nuclei, or does not occur at all, according to the type of salt. A probable explanation is presented on the basis of the trend of ΔT/νmK vs. m.     

Novel liquid-crystalline derivatives of transition metals. The effect of the molecular geometry of the ligands on the mesogenic properties of tetracoordinated copper(II) complexes

The synthesis, characterization and thermal behaviour of several new series of copper(II) complexes derived from carbonylic compounds and their Schiff's bases are reported. The complexes are of two types; [Cu(C₆H₃O(R)-C(X) = O)₂], (type I) and [Cu(C₆H₃O(R)-C(X) = N-R')₂] (type II) where R = - OOC-C₆H₄OC₁₀H₂₁-p, and the position of R is 4 or 5; R' = CH₃, n-C₁₀H₂₁, p-n-C₁₀H₂₁O(C₆H₄)-; X = H, CH₃. In type I complexes, only the compound with X = H and R in position 5 showed mesomorphism. For type II complexes, all the Schiff's bases complexes of copper(II) derived from 2,4-dihydroxybenzaldehyde showed thermotropic mesophases (smectic C and nematic), whereas the complexes derived from 2,5-dihydroxybenzaldehyde were only mesogenic when the imine was derived from methylamine. None of the complexes derived from the ketone (2,4 or 2,5-dihydroxy derivatives) showed liquid-crystalline properties. X-ray studies of four complexes of type II were carried out. The anisotropy of the magnetic susceptibility has a negative sign for complexes with R in position 4 and a positive sign for 2,5-derivative complexes. The relationship between molecular structure and mesomorphic behaviour is discussed.     

Synthesis and liquid crystal properties of dinuclear cyclopalladated 5-alkyl-2-(4'-alkoxyphenyl)pyrimidine and 3-(4'-alkoxyphenyl)-6-alkoxypyridazine complexes

The dinuclear cyclopalladated complexes [Pd(L₁ or L₂)(µ-X)]₂ (HL₁=5-alkyl-2-(4'-alkoxyphenyl)pyrimidine, HL₂=3-(4'-alkoxyphenyl)-6-alkoxypyridazine, X=Cl^-, CH₂ClCOO^-, CH₂BrCOO^-, CH₃CHBrCOO^-, CH₂BrCH₂COO^-, CH₃COO^-) have been synthesized and characterized; their mesogenic properities were determined by DSC and polarizing microscopy. The effect of the bulk and the polarity of the bridging ligands on their mesogenic properties is discussed. The effect of the length of the alkyl chains on the mesogenic properties of these organometallic complexes has also been investigated.     

溴代烷烃与活性氮的反应发光研究

在流动余辉装置上, 利用N₂空心阴极放电制备活性氮, 研究了活性氮与溴代烷烃(CHBr₃、CH₂Br₂、C₂H₅Br、C₄H₉Br) 反应的化学发光.上述所有反应中, 在550～750 nm波段均观察到了较强的NBr (b¹Σ+→X³Σ^-)跃迁发射谱. 同时在活性氮与CHBr₃和CH₂Br₂的反应中, 在流动管下游还观察到了CN (A²π, B²π→X²Σ⁺)的发射谱. 验证性的实验表明, 激发态NBr (b¹Σ⁺)是由二步过程形成: N(⁴S)与溴代烷烃反应生成NBr (X³Σ^-), 再通过N₂ (A ³Σ_u⁺)分子能量转移到激发态NBr (b¹Σ⁺); 而激发态的CN是通过N(⁴S) + CBr→CN(A, B) + Br过程形成的.     

Dimerization of polar smectics A1 with a terminal cyano group in the matrix of smectics A1 of lower polarity

Binary mixtures have been studied of polar compounds with smectic A₁ phases belonging to the following series: 4-cyanobiphenyl 4-yl 4'-n-alkylbiphenyl-4-carboxylate (CBnAB) and 4-(trans-4-n-decylcyclohexyl) benzoates (10XPCHB) with X = F, NCS, COCH₃. In these systems a strong destablization of the smectic A₁ phase is observed on the side of the CBnAB component and an enhancement of the smectic A₁ phase on the side of 10XPCHB. It is shown that the anomalous behaviour of the mixtures of two A₁ smectics with a similar layer spacing is due to the dimerization of CBnAB in the matrix of 10XPCHB which is of lower polarity.     

Heterocyclic columnar pyrimidines: synthesis, characterization and mesomorphic properties

The synthesis, characterization, and mesomorphic properties of two series of heterocyclic compounds derived from a pyrimidine core are reported. These series, 1a and 1b, are substituted with a variety of functional groups (X=NHSO₂CF₃, F, Cl, Br, I, OCH₃, CH₃, C₂H₅) at the C^3' (meta)- or C^4' (para)-position of the terminal phenyl ring, and the substituent effect on mesophase formation was studied. The compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis, and the mesomorphic behavior of the compounds was characterized and studied by differential scanning calorimetry, polarizing optical microscopy and powder X-ray diffraction. Most of the compounds were mesogenic at room temperature, and the mesophases were assigned as lamellar columnar (Col_L) phases, as expected for disk-like molecules. The results also revealed that compounds with a para-substituent (1a; except for -OCH₃) at the C^4'-position, exhibited higher clearing temperatures and wider temperature mesophase ranges than those of compounds with a meta-substituent (1b) at the C^3'-position. The higher clearing temperatures may be attributed to stronger dipolar interactions resulting from a greater resonance effect with the central core for para-substitution than for meta-substitution. The results also indicated that the columnar mesophases observed show a correlation with the electronic properties of the substituents; compounds containing electron-withdrawing substituents (X=F, Cl, Br, I, NHSO₂CF₃) also have higher clearing temperatures than compounds containing electron-donating substituents (X=Me, Et, OMe).     

The effect of terminal chain modifications on the mesomorphic properties of 4,4'-disubstituted diphenyldiacetylenes

A variety of terminal chain modifications (Y) were made on the diacetylenes in which X=C_nH_2n+1, C₁₂H₂₅O and F, and Y=CH₂CH(Me)C₂H₅, COCH₃, C≡CC₅H₁₁, C_nF_2n+1C_nH_2n+1 and CH=CHCO₂C₃H₇. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These were compared with those for the dialkyl analogues (X=C_mH_2m+1, Y=C_nH_2n+1) and a series of 1- and 2-olefins (Y=CH=CHC_nH_2n+1 and CH₂CH=CHC_nH_2n+1). The 1-olefin series showed wider range nematics than the dialkyl compounds, whereas the above modifications showed either narrow range nematic phases, no mesophase or higher melting temperatures. New transition temperature and enthalpy data are provided for some of the dialkyl and F-alkyl compounds previously reported, for comparisons. Preliminary birefringence data are also included along with the results of some heat and UV stability studies.     

Sulphur containing mesogens. The mesophasic behaviour of di(4-alkyloxybenzoates) of 4,4'-dimercaptobiphenyl

A homologous series of di(4-alkyloxybenzoates) of 4,4'-dimercaptobiphenyl: CH₃(CH₂)_n-1O-C₆H₄-COS-C₆H₄-C₆H₄-SOC-C₆H₄-O(CH₂)_n-1CH₃,n=1-7, has been synthesized and the thermotropic liquid-crystalline behaviour investigated. All compounds exhibit enantiotropic mesomorphism over a remarkable temperature range. While the mesophase thermal stability is moderately higher than that found for the corresponding oxygenated analogues, the smectic stability is definitely lower. In fact, all the compounds are nematic but smectic mesomorphism (S_C) is observed for n = 7. Compounds with n = 6 or 7 exhibit enantiotropic highly ordered smectic (or disordered crystal) phases, probably S_G in type.     

New organometallic liquid crystals I. Orthopalladated imine derivatives

The synthesis, characterization and thermal behaviour of 12 dinuclear, orthopalladated complexes derived from Schiff's bases are reported. The complexes are of the type [Pd₂(H-X)₂C₆H₃(OR)-C(Z) = N-C₆H₄R'₂] (X = OAc, Cl, Br, SCN; Z = H, CH₃; R' = OR, R; R = C₁₀H₂₁) and ten of them exhibit ordered mesophases (S_C and S_A). The molecules were characterized structurally by I.R. and ¹H N.M.R. spectroscopy in order to elucidate the possible existence of isomers. The connection between their molecular structures and their mesogenic properties is discussed.     

Experimental study and modelling using the ERAS-Model of the excess molar volume of acetonitrile–alkanol mixtures at different temperatures and atmospheric pressure

Densities of {(1−x)CH₃(CH₂)_n−1OH + xCH₃CN} for n=1, 2, 3 or 4 have been determined as a function of composition at 288.15, 293.15, 298.15 and 303.15 K at atmospheric pressure using a vibrating-tube densimeter (Anton Paar DMA 4500, resolution 1×10⁻⁵ g cm⁻³). Excess molar volumes were calculated. The V_m^E values were negative for acetonitrile–methanol mixtures and sigmoid for acetonitrile–alkanols (C₂–C₄) mixtures over the complete mole fraction range. V_m^E values increase in a positive direction with increase in chain length of the alkanols and with the temperature. The Extended Real Associated Solution Model (ERAS-Model) calculations allowing for self-association for the alkanols and complex formation between acetonitrile and alkanols have been used to correlate experimental data. The model is able to reproduce the asymmetrical V_m^E behavior of the studied systems, although agreement between theoretical and experimental values is less satisfactory for some concentration ranges.     

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.     

New mesomorphic organocyclosiloxanes I. Thermal behaviour and mesophase structure of organocyclotetrasiloxanes

cis-Cyclotetrasiloxanes of the formula cis-[PhSi(O)(OSiMe₂R)]₄ with R = Me, CH₂Cl, CH CH₂ and cis-[ClC₆H₄Si(O)(OSiMe₃)]₄ were synthesized and investigated in terms of their thermotropic phase transitions. Two ordered phases were observed for the cis-cyclotetrasiloxanes, one at lower temperature exhibiting the properties of a crystal and one at higher temperature exhibiting the properties of a plastically crystalline (3D) mesophase. A detailed examination of the mesophase behaviour and mesophase structure of octaphenylcyclotetrasiloxane was also carried out. It was shown that the thermal properties and structural characteristics of the mesophase are influenced by the structural characteristics of the substituent attached at the silicon atom in the tetracyclosiloxane. The new mesomorphic cis-cyclotetrasiloxanes are by far the largest molecules reported to date as forming plastic crystals, and the temperature region of the mesophase is much broader than in other plastic crystals. All five cyclotetrasiloxanes studied were found to be isomorphous in the 3D-mesophase and the low temperature forms of the two cis-cyclotetrasiloxanes: PhSi(O)(OSiMe₂R)₄ (R = Me, CH CH₂) were also isomorphous.     

Non-symmetric bent-core mesogens with one terminal vinyl group

Two series of non-symmetric banana-shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3-phenylene bis(4-benzoyloxy)benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC₈H₁₇ to OC₁₆H₃₃. The other terminal tails are OC₁₁H₂₃, O(CH₂)₉CH = CH₂, OC₁₀H₂₁ and O(CH₂)₈CH = CH₂. The short-tailed compounds show monotropic or enantiotropic B₁ phases and the long-tailed compounds the B₂ phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B₂ phases have layer spacings that suggest a tilt of ∼45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric.     

Conductivity, calorimetry and phase diagram of the NaHSO4–KHSO4 system

Physico-chemical properties of the binary system NaHSO₄–KHSO₄ were studied by calorimetry and conductivity. The enthalpy of mixing has been measured at 505 K in the full composition range and the phase diagram calculated. The phase diagram has also been constructed from phase transition temperatures obtained by conductivity for 10 different compositions and by differential thermal analysis. The phase diagram is of the simple eutectic type, where the eutectic is found to have the composition X(KHSO₄) = 0.44 (melting point ≈ 406 K). The conductivities in the liquid region have been fitted to polynomials of the form κ(X) = A(X) + B(X)(T − T_m) + C(X)(T − T_m)², where T_m is the intermediate temperature of the measured temperature range and X, the mole fraction of KHSO₄. The possible role of this binary system as a catalyst solvent is also discussed.     

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.