Alkyl chain self ordering,induction and suppression of mesophase by Cu(II) containing [1,2,3]-triazole-based bidentate salicylaldimine ligands: synthesis,characterisation and X-ray diffraction studies

Some new Cu(II) complexes containing [1,2,3]-triazole-based bidentate salicylaldimine and its analogues with terminal substituent (F, Cl, Br and I) have been synthesieed. All the target complexes and their uncoordinated ligands were elucidated by elemental analysis and spectroscopic techniques (UV-visible, FT-IR, 1D, 2D ¹H and ¹³C-NMR). The polarising optical microscope and differential scanning calorimetry (DSC) have disclosed all complexes and ligands are mesomorphic except the complex without any terminal substituent. The fluoro-substituted complexes with even parity C₁₄H₂₉ and C₁₆H₃₃ exhibit new enantiotropic nematic phase which was absent in their corresponding ligands, whereas the suppression of SmC phase occurred for all complexes with longer C₁₆H₃₃ and C₁₈H₃₇. X-ray diffraction confirmed the existence of SmA, SmC and N phases for complexes and ligands. The other notable feature is that the self-ordering of terminal alkyl chain occurred in SmA and SmC phases of complexes with even terminal alkyl chain ranging from C₁₄H₂₉ to C₁₈H₃₃. Their corresponding ligands exhibit intercalated structure of SmA and SmC phases. The thermal behaviour studies show that the fluoro-substituted triazole-based complexes possess lowest phase transition temperature and more stable as compared to other substituent which decomposed during the isotropisation.     

含亚胺和胆甾烯基不对称液晶二聚体的合成及介晶性

报道含亚胺和胆甾烯基不对称液晶二聚体化合物XC₆H₄N＝CHC₆H₄OC₁₀H₂₀COOCh* [X＝OC_nH_2n＋1, (n＝1～12,14), F, Cl, Br, CH₃] (1a～1q)的合成及液晶性. 目标化合物通过600 MHz ¹H NMR和元素分析进行了结构表征. 其介晶性通过偏光显微镜(POM)和差示扫描量热计(DSC)进行了研究. 结果显示: 所有化合物都具有胆甾相(N*). 对于烷氧基系列(X＝OC_nH_2n＋1), 有部分化合物还呈现了近晶A相(S_A), 且随着末端烷氧链长度的增加, 化合物的清亮点呈现缓慢下降的趋势, 而化合物从胆甾相到各向同性液体转变的熵变(ΔS_N*→I)则呈现奇-偶效应. 同时我们对比研究了取代基X对胆甾相稳定性的影响, 发现取代基X对胆甾相的稳定性高低顺序为: MeO＞Cl＞Br＞Me＞F. 这些结果证实了末端取代基的改变对化合物的相转变温度以及介晶性质有显著的影响.     

Structure property and mesomorphic behaviour of S-shaped liquid crystal oligomers possessing two azobenzene moieties

A new series of symmetrical S-shaped oligomers 4,4?-bis(ω-2-(ω-[(bromophenyl)diazenyl]-alkoxy)phenoxy)hexylbiphenyl consisting of two different spacers (inner -(CH₂)₆- and outer -(CH₂)_n-) have been synthesised. Their physical, thermal and texture observation over various transition temperatures are reported. The outer spacers for these compounds vary from n = 4 to n = 9. The oligomers with even number of members exhibit monotropic phase in which the compound with n = 4 shows nematic (N) phase whilst those with members n = 6 and 8 exhibit N and smectic A (SmA) phases. However, the homologs with odd number of members display enantiotropic phase in which the compound with n = 5 exhibits N and smectic phases whereas the members with n = 7 and 9 are predominantly smectogenic. The temperature range of N phase for even-numbered member decreased with elongation of the outer spacer. The smectic phase stability among the members in the present series increases when the outer spacer n is increased from 5 to 8.     

Synthesis,characterisation, mesomorphic investigation and temperature-dependent Raman study of a novel calamitic liquid crystal: methyl 4-(4′-n-alkoxybenzylideneamino)benzoate

A new series of Schiff base calamitic liquid crystal; methyl 4-(4′-n-alkoxybenzylideneamino)benzoate (MABAB), H_2n+1C _n OC₆H₄C(H)=NC₆H₄COOCH₃ (n = 6, 8, 10, 12, 14, 16) has been synthesised and characterised by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy. The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All members of the series exhibit enantiotropic smectic A (SmA) mesophase. Temperature-dependent micro-Raman study of one of the members, MABAB-10 has been employed to identify phase transitions and the molecular rearrangement therein. Analysis of Raman marker bands; C–H in-plane bending, C–C stretching of phenyl rings and –C(H)=N– linking group of core confirms the transitions clearly as observed through DSC and POM. An in situ Raman measurement of C–H in-plane bending mode has also been performed to visualise the molecular changes more clearly. The Raman study gives an evidence of induced co-planarity of rings at Cr→SmA phase transition. The density functional theoretical (DFT) optimisation of monomer, dimer and rotational conformer of MABAB-10 also support the induced co-planarity at Cr→SmA phase transition.     

Thermotropic liquid–crystalline properties of 4,4′-dialkoxy-3,3′-diaminobiphenyl compounds and their precursors

A series of 4,4?-dialkoxy-3,3?-diaminobiphenyl compounds were synthesised by three-step procedure that involves alkylation, nitration and reduction reactions. Their chemical structures were characterised by FTIR, ¹H and ¹³C spectroscopy and elemental analysis. Their thermotropic liquid–crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VT-XRD). The 4,4?-dialkoxy-3,3?-dinitrobipheyl compounds, precursors to the diamine compounds, were also examined for their thermotropic LC properties. POM studies of focal conic textures and VT-XRD of the 3,3?-diaminobiphenyl derivatives having flexible alkyl chains (C₆–C₁₂) exhibited the smectic A (SmA) phase independent of the length of alkyl chains. Similarly, the 3,3?-dinitrobiphenyl derivatives containing alkyl chains C₇, and C₉–C₁₁ exhibit the SmA phase, those containing C₈ formed the smectic C (SmC) phase and C₁₂ formed both the SmA and smectic B (SmB) phases, respectively. The 3,3?-diaminobiphenyl derivatives had excellent thermal stability in the temperature range of 237–329°C, while those of 3,3?-dinitrobiphenyl derivatives were in the temperature range of 270–321°C. The 3,3?-diaminobiphenyl derivatives emitted UV light both in chloroform and acetonitrile.     

新型含氧亚甲基和亚胺桥键的液晶化合物的合成及介晶性

报道一类新的、结构通式为MeO₂CC₆H₄CH₂OC₆H₄CH＝NC₆H₄Y, Y＝OC_nH_2n＋1, Me, Cl, Br, NO₂, H 的棒状液晶化合物的合成. 通过DSC和偏光显微镜对其介晶性研究发现, 除Y＝H外, 这些化合物均具有介晶性. 当Y为非烷氧基时, 呈向列相液晶; 当Y为较短的烷氧基时(n＝1～3), 液晶化合物具有向列相(N); Y为较长烷氧基时(n＝4～16 ), 液晶化合物只有近晶B相(S_B)和近晶A相(S_A); S_A-I相变的熵变随烷氧链原子数而奇-偶变化, 但与N-I相变的“奇-偶效应”相反.     

含氧亚甲基中心桥键席夫碱型液晶化合物的合成及介晶性

报道了两个系列含氧亚甲基中心桥键席夫碱型棒状液晶化合物的合成, 其结构通式为: XC₆H₄N＝CHC₆H₃(Y)OCH₂C₆H₄COOC₁₆H₃₃, Y＝H, OCH₃; X＝OC_nH_2n＋1 (n＝1～12, 14, 16), Me, F, Cl, Br. 通过热台偏光显微镜和DSC对其介晶性进行了研究. 结果显示分子中末端烷氧基链长的变化和苯环侧向取代基Y对这些液晶化合物的介晶性有重要影响.     

Banana‐shaped molecules with 4,6‐dichlorinated central core: effect of lateral substituents and terminal chains on the formation of antiferroelectric smectic mesophases

Six banana‐shaped compounds with a central core based on a 4,6‐dichloro‐1,3‐phenylene group were synthesized by varying the terminal chains (R = OC₁₀H₂₁ or OC₁₁H₂₁) and the lateral substituents (X = H, F or Cl). Their mesophases were characterized by a combination of differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X‐ray diffractometry. Mesomorphic properties of the banana‐shaped mesogens with an olefinic group (R = OC₁₁H₂₁) as a terminal chain are sensitive to lateral halogen substituents as much as those of the analogues with a saturated group (R = OC₁₀H₂₁). The compounds with X = F showed an antiferroelectric switchable smectic phase, which has been designated a B₂ phase. The compounds without a lateral halogen substituent only formed a nematic phase, while the compounds with X = Cl did not exhibit a mesophase in the melt.     

Organomonophosphines in PtP<Subscript>2</Subscript>XY derivatives: structural aspects

This review covers over two hundred Pt(II) complexes with a PtP₂XY inner coordination sphere, in which the P-donor ligands are organomonophosphines. These complexes can be divided into six groups: PtP₂HX (X = O, N, B, Cl, S, Br, Se, Si, or I); PtP₂OX (X = N, Cl, S, or Se); PtP₂NX (X = CN, Cl, B, S, Br, Se, or Te); PtP₂BX (X = F, Cl, S, Br, or I); PtP₂ClX (X = S, Se, Si, As, or Te); and PtP₂SiX (X = Br or Te). The complexes crystallize in several crystal systems: hexagonal (×1), tetragonal (×1), orthorhombic (×22), triclinic (×78), and monoclinic (×130). There are complexes with cis-configuration and trans-configuration, the latter by far prevails. Besides monodentate ligands, there are also heterobidentate ligands with: O/N, O/S, O/Se, N/S, N/Se, and N/Te, donor sites. These chelating ligands form a wide variety of metallocyclic, four-, five-, and six-membered rings, and the effects of both steric and electronic factors can be seen from the values of the L–Pt–L bite angles. The structural parameters are analyzed and discussed with particular attention to trans-influences.     

Heterocyclic pyridine-based liquid crystals: synthesis and mesomorphic properties

A series of new calamitic liquid crystals, 4-{[(pyridin-4-yl)methylidene]amino}phenyl 4-alkoxybenzoates comprising a heterocyclic (pyridine) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were synthesised and characterised. This series consists of nine members wherein the members differ by the length of alkoxy chain (C_nH_2n+1O–, where n = 2, 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviours were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first three members of the series (n = 2, 4 and 6). As the alkoxy chain increased to n = 8 and n = 10, the nematic phase appeared together with an additional smectic A (SmA) phase. When moving from n = 12 until the highest members (n = 18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA).     

The effect of terminal substituents on crystal structure,mesophase behaviour and optical property of azo-ester linked materials

A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH₃, –OC₂H₅ and –OC₃H₇) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R¹₂(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R²₂(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH₃, –OC₂H₅ and –OC₃H₇) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λ_max) of nearly 370 nm.     

有玻璃态和液晶态的胆甾烯基苯并菲的合成及介晶性

将盘状液晶基元苯并菲与手性向列型液晶基元胆甾烯基结合的化合物, 可望出现全新的性质. 合成了含有胆甾烯基的苯并菲化合物C₁₈H₆(OC₅H₁₁)₅(OC₅H₁₀COOCh) (2), 2,7-C₁₈H₆(OC₅H₁₁)₄(OC₅H₁₀COOCh)₂ (4), C₁₈H₆(OR)₃(OC_nH_{2nCOO- Ch)3 (R＝C5H11, C7H15, C9H19, C11H23, n＝1, 5, 10) (6a～6f), C18H6(OC5H10COOCh)6 (Ch: cholesteryl) (8). 偏光显微镜和差示扫描量热法对这些化合物的热致介晶性研究结果显示, 化合物 4, 6a～6e具有手性盘状向列相和玻璃态, 8呈现近晶B相(SB)和玻璃态. 随间隔基长度n和烷基链R碳原子数的增加, 化合物玻璃化温度和清亮点呈下降趋势. 随着胆甾烯基数目减少, 化合物的玻璃化温度和清亮点降低.}     

Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X₃SiSiMe₃ (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H₃SiSiMe₃), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F₃SiSiMe₃), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl₃SiSiMe₃) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br₃SiSiMe₃), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C _3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X₃SiSiXMe₂ (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.     

Synthesis and mesomorphic behaviours of a homologous series of 2-(4-alkyloxybenzylidenamino)benzothiazoles

The synthesis and characterisation of a series of new rod-shaped liquid crystal (LC), 2-(4-alkyloxybenzylidenamino)benzothiazoles possessing even number of carbon atoms at the alkyloxy chain (C_nH_2n?+?1O-, n = 2, 4, 6, 8, 10, 12, 14, 16, 18) are reported. The molecular structures of title compounds were elucidated using FTIR and nuclear magnetic resonance spectroscopic techniques. The phase behaviour of these new compounds was characterised and studied by differential scanning calorimetry and polarising optical microscopy. Lower members (n = 2, 4 and 6) did not exhibit mesophase. Octyloxy derivative was monotropic LC. Enantiotropic smectic A phase was observed from n-decyloxy derivatives onward to the last homologous synthesised.     

Induction of ionic smectic C phases: a systematic study of alkyl-linked guanidinium-based liquid crystals

A series of ionic liquid crystals with an alkoxy biphenyl unit tethered via an alkyl spacer to a guanidinium head group were synthesised and the mesomorphic properties were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction (XRD; WAXS and SAXS). Whereas all symmetrical guanidinium chlorides with the same chain lengths in alkyl tail and spacer displayed enantiotropic SmA₂ phases, monotropic SmC₂ phases with 1–2 K temperature range were only formed for chain lengths ≥ C₁₀. Shifting the calamitic core more closely to the ionic head group by decreasing the tether length and simultaneously increasing the terminal alkyl chain improved the stability of both SmA and SmC phases considerably and led to enantiotropic SmC phases for the guanidinium chloride with C₁₄ alkyl tail and C₆ spacer. An even more pronounced effect was detected during anion exchange. Bromide, iodide, hexafluorophosphate, thiocyanate and triflate suppressed any SmC phase, whereas tetrafluoroborate behaved similar to chloride maintaining the SmC phase. However, acetate stabilised the SmC phase at the expense of the SmA phase. Based on temperature-dependant XRD measurements, a bilayer structure was proposed.     

The first series of ferroelectric steroidal fluorinated liquid crystals

A series of cholesteryl p-perfluoroalkylphenyl carbonate (CPC) [C₂₇H₄₅OCO₂C₆H₄(CF₂)_nF, n=1,4,6,8] liquid crystals was synthesized and their phase transition behaviours were studied. The results show that the compounds containing a not too long perfluoroalkyl chain (n=6,8) have monotropic chiral smectic C phases.     

Morphological phase behaviour under pressure of polycatenar mesogens with a perfluorinated moiety

Two polycatenar materials composed of a four‐aromatic‐ring core with a perfluorinated moiety attached in one terminal position through either butylene‐ or pentylene spacer groups, and three tetradecyloxy chains at the other end (abbreviated as 14PC₄F and 14PC₅F), were investigated to study the effect of pressure on the phase transition behaviour. A polarizing optical microscope equipped with a high pressure optical hot stage, was used for the purpose. The T vs. P phase diagrams of 14PC₄F and 14PC₅F were constructed in the pressure region up to 100 MPa. 14PC₄F showed the stable crystal (Cr₁)–columnar tetragonal (Col_tet)–smectic A (SmA)–columnar hexagonal (Col_h)–isoropic liquid (I) phase transition sequence under all pressures. 14PC₅F exhibited the phase sequence metastable crystal (Cr₂)–cubic (Cub)–Col_tet–SmA–I in a melt‐cooled sample on heating under pressure. But when the melt‐cooled Cr₂ sample was annealed at 52–54°C for 2–3 h, the stable crystal (Cr₁) was formed slowly, giving a stable Cr₁–Cub–Col_tet–SmA–I phase sequence. The temperature region of the stable cubic phase broadened with increasing pressure. Furthermore a new mesophase of 14PC₅F was pressure‐induced between the I and SmA phases on cooling at pressures above about 16 MPa. Since the monotropic mesophase exhibited a texture very similar to that of the high temperature Col_h phase of 14PC₄F with planar orientation, the new phase was assigned at a high temperature columnar hexagonal phase of 14PC₅F.     

Liquid-crystalline CuII and PdII complexes with nonmesogenic ferrocene-containing β-aminovinyl ketone

New liquid-crystalline heteropolynuclear complexes L₂M (M=Cu²⁺ (2a), Pd²⁺ (2b)) were synthesized by the reactions of C₅H₅FeC₅H₄−C₆H₄NH−C₂H₂−(CO)−C₆H₄OC₁₂H₂₅ (1, LH) with copper(ii) and palladium(ii) acetates. Compound2b was found to possess monotropic nematic and smectic phases;2a exhibits the monotropic nematic phase and a phenomenon of “double melting”. The compositions and structures of compounds1 and2a,b were established by elemental analysis,¹H and¹³C NMR, ESR, and IR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 381–383, February, 1999.     

Synthesis and smectogenic properties of novel phloroglucinol-based star-shaped liquid crystals containing three peripheral alkyloxylated Schiff base arms

A series of symmetrical trimeric liquid crystalline compounds of which the molecular structure with a central core of 1,3,5-benzene attached by three rod-like mesogenic Schiff base moieties via the propylene spacers and ether linkages has successfully been synthesised and characterised by infra red and nuclear magnetic resonance spectroscopic techniques. All the star-shaped compounds in this series exhibit predominantly SmC phase except the analogue possessing terminal C₈H₁₇ group. It is apparent that the members with even parity from C₁₀H₂₁ to C₁₆H₃₃ show enantiotropic SmC phase while the member with longest terminal chain of C₁₈H₃₇ is inclined to monotropic smectogen. The X-ray diffraction measurements reveal that the tilted smectic layer structures of the SmC phase are confirmed to have an obvious sharp peak at small angles of 2θ ～ 1.03°–1.48° with d-spacing values of 4.01–4.58 nm, which are corresponding to tilt angles of ～48° in the SmC phase.     

Mutual enhancing effects of the σ-hole interactions and halogen/hydrogen-bonded interactions in the iodine-ylide containing complexes

The region of positive electrostatic potentials (σ-hole) has been found along the extension of the C–I bond in the iodine-ylide CH₂IH, which suggests that the iodine-ylide could interact with nucleophiles to form weak, directional noncovalent interactions. MP2 calculations confirmed that the I···N σ-hole interaction exists in the CH₂IH···NCX (X = H, F, Cl, Br, I) bimolecular complexes. The NCCl···CH₂IH···NCX (X = H, F, Cl, Br, I) termolecular complexes were constructed to investigate the weakly bonded σ-hole interactions to be strengthened by Cl···C halogen bond. And then, the NCY···CH₂IH···NCCl (Y = H, F, Cl, Br, I) termolecular complexes were designed to investigate the enhancing effects of the I···N σ-hole interaction on the Y···C halogen/hydrogen-bonded interactions. Accompany with the mutual enhancing processes of the σ-hole interactions and halogen/hydrogen-bonded interactions in the iodine-ylide containing termolecular complexes, both the I···N σ-hole interactions and Y···C halogen/hydrogen-bonded interactions become more polarizable.