A new series of nematic and smectic liquid crystals with negative dielectric anisotropy: the effect of terminal chain substitution on thermal and electro-optical properties

Two alkyl (1b and 1c) and four fluoroalkyl derivatives (1d-1f) of 4-arylbutyric acid (1c, 1d and 1e) and 4-arylbutanol (1b, 1f and 1g) [aryl = 2',3'-difluoro-4'-(2-(E-4-pentylcyclohexyl)ethyl)-biphenyl-1-yl] were prepared and investigated in the pure form as nematic materials (1b and 1c) and as additives to a ferroelectric liquid crystal (FLC) host (1d-1f). A comparison of 1b and 1c with the decyl analogue 1a demonstrates the effect of terminal chain modification on thermal and electro-optical properties. The substitution of the -CH₂O- (1b) or -COO- (1c) for -CH₂CH₂- in 1a destabilized the N and SmA phases or completely eliminated the smectic behaviour (1c). Dielectric analysis revealed that the chain modification increased the negative Δε, reduced elastic constant K ₁₁ and moderately decreased rotational viscosity γ₁. The temperature dependence of the key electro-optical parameters was analysed for ester 2, the methyl analogue of 1c, which exhibits a 45 K wide N phase. All four fluoroalkyl derivatives 1d-1f showed enantiotropic SmA phases and 1e also exhibited a monotropic SmC phase. Solutions of 1d-1f in a FLC host (0.2 mmol g^-1) increased the tilt angle Θ (up to 45° for 1g), reduced rotational viscosity γ₁ and the risetime τ. The most dramatic changes were observed for 1g, which contains 15 fluorine atoms.     

Synthesis and mesomorphic behaviour of novel discotic meso-tetra(3,4,5-n-trialkoxybenzoylaminophenyl)porphyrins

Novel porphyrin derivatives with twelve flexible alkyl chains, namely meso-tetra[4-(3,4,5-n-trialkoxybenzoylamino)phenyl]porphyrins (1a, n = 12; 1b, n = 16) and the zinc complex (2a) were synthesized. The mesomorphic properties were investigated by DSC, WAXD and polarizing optical microscopy; the results showed that 1a and 2a exhibit a pseudo-hexagonal columnar phase, and 1b a rectangular (Col) phase over a wide temperature range including room temperature.     

Crystal-smectic E mesophases in a series of 2-(4-n-alkylphenyl)indenes

A series of 2-(4-n-alkylphenyl)indenes (3) with different alkyl substituents (CH₃ to C₁₀H₂₁) were synthesized and systematically characterized using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction compared with 2-phenylindene (3a). Depending on the alkyl chain length, highly ordered crystal-smectic E mesophases were observed and confirmed by X-ray diffraction for the derivatives 3h-3k with heptyl to decyl chains (n = 6-9). For 3f with a pentyl side chain (n = 4), an X-ray crystal structure analysis was carried out.     

A comparison of mesogenic properties of p-carborane-1,12-dicarbaldehyde schiff's bases with their terephthaldehyde analogues

A homologous series of carborane-containing Schiff's bases 1A[n] (n = 1-10) was prepared and compared with the analogous series 1B[n] derived from terephthaldehyde. An exponential fit of the T _NI values for both series yielded a quantitative assessment of the effect of ring structure on mesophase stability. This includes the T _NI value for n→∞ (86°C for 1A[n] and 209°C for 1B[n]) and steepness of descent (0.135 for 1A[n] and 0.095 for 1B[n]). The difference in behaviour of the two series was attributed, largely, to conformational properties of the central rings A and B. Electronic interactions between the central rings and the π-substituents were investigated by UV spectroscopy and by quantum-mechanical calculations. The effect of replacement of O with CH₂ in the terminal chain of 1[n] on the namatic phase stability was assessed for n = 5-7.     

On the thermal behaviour of palladium (II) macrocyclic polycatenars

Polycatenar saturated macrocycles 1,10-bis[3,4,5-tris(4-dodecyloxy)benzoy1]-1,10-diaza-4,7,13,16-tetrathiacyclo-octadecane (3b) and 1,10-bis[3,4-bis(4-dodecyloxy)benzoy1] -1,10-diaza-4,7,13,16-tetrathiacyclo-octadecane (3d) reacted with [Pd(MeCN)₄][BF₄]₂ led to the cationic complexes [4b][BF₄]₂ and [4d][BF₄]₂, respectively. Complexes [4b][BF₄]₂ and [4d][BF₄]₂ showed smectic mesomorphism on heating as confirmed by small angle X-ray diffraction. A concurrent, irreversible structural change of the complex cations was observed and a tentative explanation is suggested.     

A Novel Cyclization of Squalene Initiated by Radical Cation

Squalene 1 is recognized as the precursor of sterols and polycyclic triterpenoids that play important roles in numerous life processes¹. In view of the fact that the cyclization of hexa-1, 5-diene by γ-irradiation² and some isoprenoid polyenes by photochemical method³ through radical cation intermediates have been reported and that tris (p-bromophenyl)ammoniumyl hexachloroantimonate (TBPA⁺SbCl₆, 2) could oxidize olfines to the corresponding radical cations that underwent pericyclic reactions⁴, we thought it might be worthwhile to try the biomimetic cyclization of squalene initiated by radical cations. Previously we⁵ have reported the cyclization of geraniol and nerol to cis-p-mentha-2,8-dien-l-ol by reaction with 2. Herein, we report the cyclization of 1 initiated by 2 in dry dichloromethane to give 20-R-protosta-5,24-diene 3a and 20-S-protosta-5,24-diene 3b in the ratio of 1:1 with the total yield of 20%(Scheme 1).     

Three-phase extraction study of cyanex 923-n-heptane/H(2)SO(4) system

Phase behavior of the extraction system, Cyanex 923–heptane/H₂SO₄–H₂O has been studied. The third phase appeared at different aqueous H₂SO₄ concentration with varying initial Cyanex 923 concentration and temperature affects its appearance. Almost all of H₂SO₄ and H₂O are extracted into the middle phase. The H₂SO₄ concentration in the third phase increases with the increasing aqueous acid concentration (C_H2SO4,b) while the water content first increases and then reaches a constant value at C_H2SO4,b=11.3 mol l⁻¹. In the region of C_H2SO4,b higher than 5.2 mol l⁻¹, the composition of the middle phase is only related to the equilibrium concentration of H₂SO₄ in the bottom phase. H₂SO₄ and H₂O are transferred into the middle phase mainly by their coordination with Cyanex 923 when C_H2SO4,b is less than 11.3 mol l⁻¹. When C_H2SO4,b is higher than 11.3 mol l⁻¹, excess H₂SO₄ is solubilized into the polar layer of the aggregates. In the region considered, the extracted complex changes from C923 · H₂SO₄ to C923 · H₂SO₄ · H₂O and then to C923 · (H₂SO₄)₂ · H₂O.     

CPI induction of liquid crystal behaviour in triphenylenes with a mixture of hydrophobic and hydrophilic side chains

2,3,6,7,10,11-Hexasubstituted triphenylenes have been synthesized that contain a mixture of hydrophobic (C₆H₁₃O) and hydrophilic (CH₃OCH₂CH₂OCH₂CH₂O) side chains. At one extreme HAT6 (1a) (six hydrophobic chains) shows thermotropic behaviour and at the other TP6EO2M (1e) (six hydrophilic chains) shows lyotropic behaviour. Of the triphenylenes with a mixture of hydrophobic and hydrophilic side chains, only the triphenylene with one hydrophilic side chain and five hydrophobic side chains (1b) gives a thermotropic columnar phase. None of the others show liquid crystal behaviour. However, all of these triphenylenes form binary 1:1 compounds when mixed with PDQ9 (2a) and with PTP9 (2b). These CPI (complimentary polytopic interaction) stabilized compounds give thermotropic hexagonal columnar phases over wide temperature ranges.     

Heterocyclic benzoxazole-based liquid crystals

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds 1a-c and a Pd complex 1d derived from benzoxazole as the core group are reported. These compounds were prepared by the ring closure reaction of 4-alkoxybenzoic acid 4-[(4-alkoxy-2-hydroxyphenylimino)methyl]phenyl esters 6 in the presence of lead(IV) acetate. All the compounds were characterized by ¹H and ¹³C NMR spectroscopies and elemental analysis. The phase behaviour of these mesogenic compounds was characterized and studied by differential scanning calorimetry and polarizing optical microscopy. All the compounds 1a exhibited nematic (N) and/or smectic C (SmC) phases, as expected for rod-like molecules; however, the compounds 1b and 1c exhibited crystal phases. For those compounds 1a having shorter carbon chains (n = 1, 3, 4) nematic phases were observed, whereas for compounds having longer carbon chains (n = 6, 7, 8, 10, 12, 14) smectic C behaviour was also observed at lower temperatures. The greater aspect ratio (l/d) of compounds 1a compared with 1b and 1c was found to be required for the observation of liquid crystallinity. The fluorescent properties of these compounds were also examined. All λ_max peaks of the absorption and photoluminescence spectra of compounds 1a-1c occurred at c. 316-322 nm and 371-382 nm, respectively. The quantum yields of some compounds were relatively low, and also slightly solvent-dependent.     

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).     

Ferroelectric liquid crystals with fluoro- and aza-fluorenone cores: the effect of stereo-polar coupling

The chiral fluorenone mesogens (R)-1-fluoro-2-(2-octyloxy)-7-(4-undecyloxybenzoyloxy)fluoren-9-one (2) and (R)-2-(2-octyloxy)-7-(4-undecyloxybenzoyloxy)-3-azafluoren-9-one (3) were synthesized using a combined ortho-directed and remote metalation strategy, which also incorporates a Suzuki-Miyaura crosscoupling step. These compounds form chiral SmC* liquid crystal phases with reduced polarizations (P _o) of +475 and +332 nC cm^-2 at 10 K below the Curie point, respectively. These values are considerably larger than that previously reported for the unsubstituted fluorenone (R)-2-(2-octyloxy)-7-(4-undecyloxybenzoyloxy)fluoren-9-one (1), which is +111 nC cm^-2 at 10 K below the Curie point. Molecular modelling based on the Boulder model suggests that the larger polarizations result from a conformational bias of the fluorenone core dipole moment along the polar axis of the SmC* phase caused by stereo-polar coupling with the chiral 2-octyloxy side chain.     

Noncentrosymmetric K2Mn3(SO4)3F2·4H2O and Rb2Mn3(SO4)3F2·2H2O with pseudo-KTP structures

Two fluoride sulfates,K₂Mn₃(SO₄)₃F₂·4H₂O(Ⅰ) and Rb₂Mn₃(SO₄)₃F₂·2H₂O (Ⅱ) are obtained by water solution method.Single-crystal X-ray diffraction analysis indicated that they crystallize in space groups of Cmc2_1.Their structures feature a pseudo-KTP structure consisting of interconnecting[Mn₃(SO₄)3F₂(H₂O)2]_∞ layers,which are further packing along the a axis with alkali metal cations balancing the charges.The structure relationships between the two compounds are discussed.Secondharmonic generation measurements manifest that Ⅰ and Ⅱ have similar second-harmonic generation responses of about 0.2 and 0.25 times that of KH₂PO₄.     

The synthesis and liquid crystalline behaviour of alkoxy-substituted derivatives of 1,4-bis(phenylethynyl)benzene

Despite the prevalence of organised 1,4-bis(phenylethynyl)benzene derivatives in molecular electronics, the interest in the photophysics of these systems and the common occurrence of phenylethynyl moeties in molecules that exhibit liquid crystalline phases, the phase behaviour of simple alkoxy-substituted 1,4-bis(phenylethynyl)benzene derivatives has not yet been described. Two series of 1,4-bis(phenylethynyl)benzene derivatives, i.e. 1-[(4'-alkoxy)phenylethynyl]-4-(phenylethynyl)benzenes (5a-5f) and methyl 4-[(4'-alkoxy)phenylethynyl-4'-(phenylethynyl)] benzoates (18a-18f) [alkoxy = n-C₄H₉ (a), n-C₆H₁₃ (b), n-C₉H₁₉ (c), n-C₁₂H₂₅ (d), n-C₁₄H₂₉ (e), n-C₁₆H₃₃ (f)] have been prepared and characterised. Both series have good chemical stability at temperatures up to 210°C, the derivatives featuring the methyl ester head-group (18a-18f) offering rather higher melting points and generally stabilising a more diverse range of mesophases at higher temperatures than those found for the simpler compounds (5a-5f). Smectic phases are stabilised by the longer alkoxy substituents, whereas for short and intermediate chain lengths of the simpler system (5a-5c) nematic phases dominate. Diffraction analysis was used to identify the SmB_hex phase in (5d-5f) that is stable within a temperature range of approximately 120-140°C. The relationships between the organisation of molecules within these moderate temperature liquid crystalline phases and other self-organised states (e.g. Langmuir-Blodgett films) remain to be explored.     

Ferroelectric liquid crystals induced by dopants with axially chiral 2,2'-spirobiindan-1,1'-dione cores: diether vs. diester side-chains

A series of axially chiral 5,5'- and 6,6'-dialkanoyloxy-2,2'-spirobiindan-1,1'-dione dopants, (R)-2 and (R)-4a-4c were synthesized in optically pure form and their ferroelectric polarization powers, δ_p, measured in four liquid crystal hosts with isotropic (I)-nematic (N)-smectic A (SmA)-smectic C (SmC) phase sequences. The results show that the sign of polarization P _S induced by (R)-2 and (R)-4a-4c follows the same trend as that previously reported for the 5,5'- and 6,6'-diheptyloxy-2,2'-spirobiindan-1,1'-dione dopants, (R)-1 and (R)-3. The polarization induced by (R)-2 in the host DFT is below detection limits, and the sign of P _S was found to invert as a function of temperature at mole fractions as low as 0.01. On the other hand, the polarization power of the 6,6'-diheptanoyloxy dopant (R)-4b in the host NCB76 is -1449 nC cm^-2, the fourth highest value reported so far, and more than three times the δ_p value of the 5,5'-diheptanoyloxy analogue (R)-2 in that host (+474 nC cm^-2). Results of ²H NMR experiments suggest that (R)-4b exerts stronger local perturbations in NCB76 than (R)-2, and that these perturbations may be chiral in nature.     

Synthesis and characterization of new liquid crystalline materials containing a non-activated arylazoindolinobenzospiropyranyl group as a chiral unit. Part II

Two series of new liquid crystalline compounds containing a non-activated arylazoindolinobenzospiropyran, ABP-SPAB 1a-1e (series 1) and SPAP-ABPC 2a-2e (series 2), have been synthesized. These LC dyes were characterized by a differential scanning calorimetry polarizing optical microscopy, X-ray diffraction and electro-optical measurements. All but one of the series 1 compounds examined exhibit monotropic second and/or third transition liquid crystal phases on cooling from the isotropic liquid. In particular, ABP-SPAB 1b shows a monotropic SmC phase, in addition to a SmA phase. In series 2, most of the compounds exhibit a monotropic nematic phase on cooling. SPAP-ABPC 2c forms an enantiotropic nematic phase and a monotropic SmA phase; 2e shows enantiotropic nematic and SmA phases.     

Unexpected Products from the Reaction of Naphthols with Cholesterol Catalysed by Montmorillonite K 10

Under catalysis of montmorillonites, arenes could be cholesterylated by cholesterol (1) via a Friedel-Crafts alkylation.¹ When phenols were employed as substrates for that reaction, aryl cholesteryl ethers were obtained instead of aryl cholestenes.² However, β-naphthol (2a) and α-naphthol (2b) gave obviously different products. We report here the identification of these unexpected products from the reaction of 2 with 1 catalysed by montmorillonite K 10.     

Synthesis and cytotoxicity of 28-carboxymethoxy lupane triterpenoids. Preference of 28-O-acylation over 28-O-alkylation of betulin by ethyl bromoacetate

28-Carboxymethoxy lupane tritepenoids 3 and 4 were synthesized by alkylation of betulin with the THP protected 2-hydroxyethyl iodide followed by oxidation and reduction.Direct reaction of betulin (5) or betulone (10) with ethyl bromoacetate led to 28-O-acylation, instead of 28-O-alkylation.The targeted compounds 3 and 4 were not cytotoxic at the highest concentrationtested (75 mmol/L), suggesting that elongation of the chain length at the 28-position in both betulinic acid (1) and betulonic acid (2)was detrimental to the cytotoxicity.The acylation products 28-O-bromoacetates (8a, 8b and 11) and 28-O-methoxyacetate 13exhibited cytotoxicity against several cancer cell lines tested.     

Crystal structures of ferro- and antiferroelectric mesogens with a 1-methylalkoxycarbonyl group

Crystal structures have been determined for 4-[(S)-1-methylpentyloxycarbonyl]phenyl, 4-([S)-1-methylhexyloxycarbonyl]phenyl 4'-octyloxybiphenyl-4-carboxylates (1 and 2, respectively) and (R)-1-methylheptyl 4-(4'-octyloxybiphenyl-4-yloxymethylene)benzoate (3), which have S_CA*, S_C* and S_CA* phases, respectively. All the crystals have a common packing mode with the previously determined structure of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC). Each crystal forms a smectic-like layer structure composed of largely bent molecules with the long alkyl chain of the chiral group almost perpendicular to the core moiety. Differential scanning calorimetry showed that the crystals of 1, 2, and MHPOBC, which have a carbonyloxy group as the central linkage between the biphenyl and phenylene moieties, transform to higher temperature solid phases in a similar temperature range (around 60°C). For 3, which has an oxymethylene linkage between the biphenyl and phenylene moieties, three kinds of solids were distinguished.     

Synthesis of Allobetulin, 28-Oxyallobetulin and Related Biomarkers from Betulin and Betulinic Acid Catalysed by Solid Acids

Betulin (1a) is an abundant natural product in the birch bark. Betulin itself currently has little usage. However, allobetulin (2a) has been used as an important intermediate in the further transformation of triterpenoids and as a sample for biological studies.¹ For example, allobetulin was further transformed to a highly active antifeedant for heliothis zea larvae. Some biomarkers (3a,b; 4a,b) with the same or similar structure as ring-E of 2a were identified in a brown coal.³ Consequently, the conversion of 1a to synthetically, biologically and geochemically more important 2a is of great significance. The transformation of 1a to 2a was reported as early as 1922 by Schulze et al in which betulin was isomerized by formic acid, involving formation and hydrolysis of allobetulin formate, to give 2a in moderate yield.⁴     

New dense fluoroalkyl-substituted imidazolium ionic liquids

New mono and polyfluoroalkyl-substituted ionic liquids have been synthesized and characterized. The neat reaction of 1-methylimidazole (1a) with 1,1,1-trifluoro-3-iodopropane (2a) at 80°C formed the quaternary salt, 1-methyl-3-trifluoropropylimidazolium iodide (3), in 90% yield. Similarly, sodium imidazole (1b) gave good yields of the quaternary salts, 1,3-bis(trifluoropropyl)imidazolium iodide (3b) with an excess of 2a, and 1,3-bis(monofluoropropyl)imidazolium bromide (3c) with an excess of 1-fluoro-3-bromopropane (2b). In water as solvent, metathesis reactions of 3 with KPF₆, LiN(SO₂CF₃)₂ and KSO₃CF_3, and of 3b and 3c with KPF₆ and LiN(SO₂CF₃)₂ led to 4a–c, 4d,e, and 4f,g, respectively, in good isolated yields. Some of the di(polyfluoroalkyl)imidazolium salts are liquids with densities in excess of 1.8 g/cm³.