溴原子取代对二茂铁液晶化合物介晶性的影响

二茂铁液晶因其独特的稳定性和易于衍生化受到研究人员的青睐[1- 8] 。我们曾经报道过一类单取代二茂铁液晶的合成与介晶性[9] 。这里我们报道另外一类二茂铁单取代液晶 ,并对分子的长度、溴原子取代对介晶性的影响进行探讨。合成路线如下 :1　实验部分ＢｒｕｃｋｅｒＡＣＥ -2 0 0ｓｐｅｃｔｒｏｍｅｔｅｒ,ＣＤＣｌ3作溶剂。ＮｉｃｏｌｅｔＭａｇｎａ-ＩＲ 5 0 0Ｓｐｅｃｔｒｏｍｅｔｅｒ,ＳｅｒｉｅｓⅡ ,ＫＢｒ压片。ＷＲＳ -ＩＡ ,ＣａｒｌｏＥｒｂａ 1 1 0ｂ。Ｐｅｒｋｉｎ -Ｅｌｍｅｒ 7Ｓｅｒｉｅｓ热分析仪 ,分温速度 1 0℃ /ｍｉ…     

High tilt antiferroelectric esters bearing a perfluorobutanoyloxy terminal chain: the influence of lateral fluoro substituents on mesomorphic behaviour,tilt angle,and spontaneous polarization

Novel liquid crystalline esters have been synthesized with a perfluorocarbonyloxy terminal chain and lateral fluoro substituents in order to determine their influence on mesomorphic behaviour, tilt angle and spontaneous polarization. Certain locations of lateral fluoro substituents provide for very low melting points and reasonably wide temperature ranges of the antiferroelectric phase, and can generate enhanced tilt angles of up to 45°, although spontaneous polarization is always lower than for the parent system without lateral fluoro substituents. Thus, these novel materials, particularly as components in mixtures, should be useful in high tilt antiferroelectric (orthoconic) applications.     

Iron(III) metallomesogen of [N2O2] donor Schiff base ligand containing 4-substituted alkoxy chains

Two new square pyramidal iron(III)-complexes of ‘salen’-type Schiff base ligands containing 4-substituted long alkoxy arms on the aromatic rings, [Fe(4-C₁₆H₃₃O)₂salcn)]Cl and [Fe(4-C₁₆H₃₃O)₂salophen)]Cl {salcn = N,N?-cyclohexanebis(salicylideneiminato) and salophen = N,N?-phenylenebis(salicylideneiminato)}, have been successfully synthesised, and their mesomorphic property investigated. The ligands and complexes were characterised by elemental analyses, UV–Vis, FT-IR, ESI–MS, ¹H and ¹³C NMR (for ligands only). The phase behaviour of the iron(III) complexes were ascertained by differential scanning calorimetry, polarising optical microscopy and variable temperature PXRD study. Ligands are non-mesomorphic, however, mesomorphism got induced upon complexation with the iron(III) centre. X-ray diffraction study revealed a layer-like arrangement of the five coordinated mesomorphic iron(III) complexes. The mesophase is stable over a wide range of temperature. The density functional theory calculations were carried out using Gaussian 09 program at B3LYP level using unrestricted 6–31G (d, p) basis set to obtain the optimised geometry of the iron(III) complexes.     

Photoluminescent nickel(II)-metallomesogens derived from salphen ligands: influence of halogens at the spacer on mesomorphism and emission properties

Three new series of photoluminescent nickel(II) metallomesogens, [NiL]; H₂L = N,N′-Bis(4-n-alkoxysalicylidene)-4-fluoro/bromo/chloro-1,2-diaminobenzene (n = 12, 14, 16) based on ‘salphen’ ligands have been synthesised and their mesomorphic and photophysical properties explored. The complexes, isolated as orange microcrystalline solids were characterised by elemental analyses, FT-IR, ¹H NMR and UV-visible spectroscopy. Thermal studies show all the compounds to be enantiotropic liquid crystals displaying columnar mesophase over a wide temperature range. Electronegativity and steric requirement of the halogen substituent at the ligand’s spacer remarkably influence the 2-D packing of the columns in the lattice in these complexes controlling the supramolecular mesomorphic order and photoluminescence. The mesophase behaviour of the fluoro-substituted complex is characterised by a transition from a columnar oblique (p1) to columnar rectangular (p2mm) phase, former stable till ambient temperature. The chloro and bromo analogues, on the other hand, displayed exclusively columnar rectangular (p2mm) mesophase with the former transforming into a glassy state and latter into a crystalline phase during cooling to ambient temperature. Molecular model based on interdigitated anti-parallel and back to back arrangements in the different columnar mesophase are proposed on the basis of X-ray diffraction (XRD) studies. The complexes emit in the blue region when excited with near UV wavelength.     

Plastic columnar mesomorphism in half-disc-shaped oxovanadium(IV) Schiff base complexes

A new series of non-disc-like oxovanadium(iv) Schiff base complexes of the type [VO((4-C _n H_2n+1O)₂salcn)], where n?=?14, 16 or 18 and salcn is N,N ^′-bis-salicylidene-1,2-cyclohexadiamine, containing 4-substituted alkoxy tails in the side aromatic rings, have been synthesised and their mesogenic properties investigated. The compounds were characterised by FT–IR, ¹H NMR, ¹³C NMR, UV–Vis and FAB mass spectrometry. The mesomorphic behaviour of the compounds was studied using polarised optical microscopy and differential scanning calorimetry. The molecular organisation in the mesophase was determined by X-ray diffraction. It was found that the ligands did not show mesogenic behaviour, but their complexes exhibited a thermally stable enantiotropic highly ordered three-dimensional plastic mesophase with a columnar structure in the extended temperature range 155–166°C. The clearing temperature of the complexes was found to be lower than in the structurally analogous copper complexes. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimised structure. A square pyramidal geometry for the vanadyl complexes has been proposed.     

New heteropolynuclear metallomesogens: copper(II), palladium(II), nickel(II) and oxovanadium(IV) chelates with [3]ferrocenophane‐containing Schiff's base and β‐aminovinylketone

New mesogenic heteropolynuclear complexes of Cu(II), Pd(II), Ni(II) and VO(IV) with the [3]ferrocenophane‐containing Schiff's base, and Cu(II) and Pd(II) complexes with the [3]ferrocenophane‐containing β‐aminovinylketone have been synthesised. The obtained heterometallic mesogenes are identified by elemental analysis, proton nuclear magnetic resonance, infrared and ultraviolet–visible spectroscopies. Liquid crystalline properties are studied by thermal polarising optical microscopy and differential scanning calorimetry techniques. Both ligands and heteropolynuclear complexes exhibit thermotropic nematic and smectic C mesophases in various temperature ranges except for the Ni(II) complex. Mesomorphism of the prepared complexes is correlated with the geometry of their central chelate core. Considerably broader mesophases and lower transition temperatures are achieved in the synthesised metallomesogens by using the alkylidene‐bridged ferrocene as a building unit.     

Dynamic and microscopic X‐ray characterization of a compound chevron layer in electroclinic liquid crystals

The local layer structure of surface stabilized electroclinic liquid crystals has been analysed by time‐resolved synchrotron X‐ray microdiffraction. At a low applied electric field, the initial bookshelf structure starts to respond above a threshold voltage. With a low to medium applied field of triangular form, the layer structure transforms reversibly between the bookshelf (low field) and the compound chevron (high field), in which the vertical and horizontal chevrons alternate along the layer. When the horizontal chevron component appears, a stripe texture can be seen in an optical micrograph. With increasing field, the horizontal chevron becomes a dominant structure while the vertical chevron still remains. The layer spacing changes in correlation with the chevron angle during the field application. At high field, surface molecules partly rearrange, resulting in alignment deterioration at the interface. The layer response time for an a.c. square wave field is of the order of a few µs to ten µs, which is close to the optical response. The appearance of the compound chevron is discussed in conjunction with the anchoring effect.     

Liquid crystalline properties of and intramolecular hydrogen bonding in 4-methyl-2'-hydroxy-4'-alkoxyazobenzenes

A homologous series of 4-methyl-2'-hydroxy-4'-alkoxyazobenzenes with chain lengths from 1 to 12 carbon atoms was synthesized and the temperatures of melting, freezing and transition from nematic to isotropic phase were determined. The main thermodynamic characteristics for those transitions were estimated. The liquid crystalline properties were compared with those of homologous series without OH groups and show a marked extension of the nematic phase for the OH substituted compounds. The spectroscopic manifestations of the hydrogenbonded OH... N chelate ring are discussed, based on a comparison of experimental and Density Functional Theory (DFT) calculated frequencies and IR intensities. The evolution of the IR absorption in the range 1540-1660 cm^-1, ascribed to the OH bending vibrations, is presented on going from the dilute CCl₄ solution through the isotropic and nematic phases to the solid state.     

Oxovanadium (IV) complexes of bidentate [N,O] donor Schiff-base ligands: synthesis and mesomorphism

A series of new oxovanadium(IV) Schiff-base complexes of the type [VO(L)₂], [L?=?N-(4-n-alkoxysalicylaldimine)-4′-dodecyloxyaniline, n?=?6, 8, 16, and 18] have been synthesized. The compounds were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, UV-Vis, FAB-mass, and magnetic susceptibility measurements. The mesomorphic behavior of the compounds was studied by polarized optical microscopy and differential scanning calorimetry. The compounds are all highly thermally stable exhibiting smectic mesomorphism. Non-electrolytic nature of the complexes was ascertained by solution electrical conductance measurements. Cyclic voltammetry revealed a quasireversible single-electron response for VO(V)/VO(IV) couple. A ν_V=O stretching mode at ～970?cm^?1 indicates absence of any intermolecular V=O?···?V=O interactions. Density functional theory study was carried out using DMol3 at BLYP/DNP level to determine energy optimized structure revealed a distorted square pyramidal geometry for the vanadyl complexes.