Mesogens with central naphthalene core substituted at various positions

We have prepared liquid crystalline materials based on hydroxynaphthalene carboxylic acids. The mutual location of both functional groups has been varied, which resulted in compounds possessing a bend angle of 120° and 60°, therefore in bent-core and V-shaped compounds, respectively. The mesomorphic properties have been established with polarizing optical microscopy, DSC measurements and X-ray investigation. The properties of the studied have been compared with analogous derivatives to establish the role of ester orientation in the vicinity of the central naphthalene core.     

Syntheses and Properties of meso‐Substituted Porphyrin Mesogens with Triazole Linkages and Peripheral Alkyl Chains

Discotic mesogens P/n‐M (n=12, 16, 18, M=2 H, Zn and Cu) bearing a porphyrin core, triazole linkages and peripheral 3,4,5‐trialkoxybenzyl units have been synthesized by a click‐chemistry approach. The thermal behavior, photophysical properties and morphologies of these compounds were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), XRD, UV and PL, SEM and TEM. These compounds can self‐assemble into hexagonal columnar phases in their pure states and form organogels in 1,4‐dioxane with unusually flower‐like sphere morphology. The supramolecular complexes of P/18‐Zn with C₇₀ or 4,7‐di‐4‐pydriyl‐2,1,3‐benzothadiazole can display hexagonal columnar phases too. Additionally, zinc porphyrin compounds P/n‐Zn show binding selectivity to Cu²⁺ among a series of cations in THF/H₂O.     

EPR characterisation of Cu(II) complexes of poly(propylene imine) dendromesogens: using the orienting effect of a magnetic field.

Liquid-crystalline derivatives of poly(propylene imine)dendrimers of the 0th, 1st and 2nd generations, complexed with copper(II) ions, were studied by EPR spectroscopy. The structures of copper (II) complexes with different Cu(II) loadings x per dendrimer ligand L (x = Cu/L) were determined. At the lowest concentration, the Cu(II) ions form monomeric complexes with approximately square-planar N2O2 coordination of both carbonyl oxygen and amido nitrogen atoms. At higher copper content, two kinds of Cu(II) complex sites with different geometries exist. The orienting effect of a high magnetic field was used to investigate the structure and magnetic properties of the copper(II) complexes. This effect, for the first time in dendrimers, allowed the resolution of five nitrogen super-hyperfine lines on g(z) components with the unusual coupling constant of a(Nz)= 35.9 x 10(-4) cm(-1). The combination of the magnetic parameters and the orienting effect indicates the presence of a monomeric complex with pseudotetrahedral N2O2 coordination of the Cu(II) ion, as well as a "dimer" structure with fivefold coordination, presumably due to an N3O2 environment. Higher copper loadings lead to increased exchange coupling between the complex sites.     

The effect of fluorine-substituted acrylate monomers on the electro-optical and morphological properties of polymer dispersed liquid crystals

The effects of fluorinated acrylate monomers on the electro-optical and morphological properties of polymer dispersed liquid crystal (PDLC) films are reported. The partial fluorination of host polymer matrices resulted in improved optical properties and better defined morphologies. An enhancement in contrast ratio was observed for fluorinated systems containing trifluoroethyl acrylate (TFEA) and hexafluoroisopropyl acrylate (HFIPA). Conversely, the incorporation of methyl acrylate (MA), a chemically similar non-fluorinated acrylate, resulted in no appreciable change in contrast ratio and an increase in relaxation time. Scanning electron microscopy morphological studies were conducted to understand further the influence of fluorinated monomers in PDLC systems.     

Polycatenar Mesogens with Various Degree of Flexibility of Molecular Structure

A series of newly synthesised rod‐like polycatenar mesogens forms columnar phases, with the number of molecules in the column cross section depending on the core rigidity. For non‐symmetric molecules, an additional density modulation, namely helical arrangement of molecules with a periodicity of approximately 10 molecular distances develops along the columns. For one of the compounds, a new type of columnar liquid crystal phase with 3D positional order is observed. Introducing a stilbene unit in the mesogenic core enhances the fluorescent properties of the compounds. In the hexagonal columnar phase, polarised light emission is observed.     

Hydrogen Bonds as Structural Directive towards Unusual Polynuclear Complexes: Synthesis,Structure, and Magnetic Properties of Copper(II) and Nickel(II) Complexes with a 2-Aminoglucose Ligand

The reaction of benzyl 2-amino-4,6-O-benzylidene-2-deoxy-α-D -glucopyranoside (HL) with the metal salts Cu(ClO₄)₂ ⋅ 6 H₂O and Ni(NO₃)₂ ⋅ 6 H₂O affords via self-assembly a tetranuclear μ₄-hydroxido bridged copper(II) complex [(μ₄-OH)Cu₄(L)₄(MeOH)₃(H₂O)](ClO₄)₃ ( 1 ) and a trinuclear alcoholate bridged nickel(II) complex [Ni₃(L)₅(HL)]NO₃ ( 2 ), respectively. Both complexes crystallize in the acentric space group P2₁. The X-ray crystal structure reveals the rare (μ₄-OH)Cu₄O₄ core for complex 1 which is μ₂-alcoholate bridged. The copper(II) ions possess a distorted square-pyramidal geometry with an [NO₄] donor set. The core is stabilized by hydrogen bonding between the coordinating amino group of the glucose backbone and the benzylidene protected oxygen atom O4 of a neighboring {Cu(L)} fragment as hydrogen-bond acceptor. For complex 2 an [N₄O₂] donor set is observed at the nickel(II) ions with a distorted octahedral geometry. The trinuclear isosceles Ni₃ core is bridged by μ₃-alcoholate O3 oxygen atoms of two glucose ligands. The two short edges are capped by μ₂-alcoholate O3 oxygen atoms of the two ligands coordinated at the nickel(II) ion at the vertex of these two edges. Along the elongated edge of the triangle a strong hydrogen bond (244 pm) between the O3 oxygen atoms of ligands coordinating at the two relevant nickel(II) ions is observed. The coordinating amino groups of the these two glucose ligands are involved in additional hydrogen bonds with O4 oxygen atoms of adjacent ligands further stabilizing the trinuclear core. The carbohydrate backbones in all cases adopt the stable ⁴C₁ chair conformation and exhibit the rare chitosan-like trans-2,3-chelation. Temperature dependent magnetic measurements indicate an overall antiferromagnetic behavior for complex 1 with J₁=−260 and J₂=−205 cm⁻¹ (g=2.122). Compound 2 is the first ferromagnetically coupled trinuclear nickel(II) complex with J_A=16.4 and J_B=11.0 cm⁻¹ (g_1,2=2.183, g₃=2.247). For the high-spin nickel(II) centers a zero-field splitting of D_1,2=3.7 cm⁻¹ and D₃=1.8 cm⁻¹ is observed. The S=3 ground state of complex 2 is consistent with magnetization measurements at low temperatures.     

Tuning the Magnetic Properties of Columnar Benzo[e][1,2,4]triazin-4-yls with the Molecular Shape

A homologous series of disc-like 1,3,6-trisubstituted benzo[e][1,2,4]triazin-4-yls 1[n] was synthesized and their structural, thermal, optical, magnetic, and electric properties were investigated. The results demonstrate that all members of the series display a Col_h phase with clearing temperatures depending on the length of the alkoxy chains at the N(1) position, hence the shape of the disc. Powder XRD and magnetic data indicate a gradual change in the column diameter and magnetic behavior in the series in transition from half-disc in 1[0] (antiferromagnetic interactions) to full-disc geometry in the 1[12] homologue (ferromagnetic interactions with J/k_B=+7.5 K). Studies of binary systems revealed that a 1 : 1 mixture of 1[0] and 1[12] exhibits modest stabilization of the Col_h phase with an expanded range, and magnetic behavior typical for 1[0] in the rigid phase obtained from the melt. Electric measurements demonstrated hole mobility of ∼10⁻³ cm² V⁻¹ s⁻¹ and dark conductivity of ∼10⁻¹¹ Scm⁻¹ in the mixture and individual compounds. The latter is enhanced up to 4 times by simultaneous illumination with UV light.     

Self‐Assembled Fibers Containing Stable Organic Radical Moieties: Alignment and Magnetic Properties in Liquid Crystals

Macroscopically oriented stable organic radicals have been obtained by using a liquid–crystalline (LC) gel composed of an l ‐isoleucine‐based low molecular weight gelator containing a 2,2,6,6‐tetramethylpiperidine 1‐oxyl moiety. The LC gel has allowed magnetic measurements of the oriented organic radical. The gelator has formed fibrous aggregates in liquid crystals via intermolecular hydrogen bonds. The fibrous aggregates of the radical gelator are formed and oriented on cooling by applying a magnetic field to the mixture of liquid crystals and the gelator. Superconducting quantum interference device (SQUID) measurements have revealed that both oriented and nonoriented fibrous aggregates exhibited antiferromagnetic interactions, in which super‐exchange interaction constant J is estimated as ?0.89 cm^?1.     

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.     

Dinuclear Complexes with Predictable Magnetic Properties

When two paramagnetic transition metal ions are present in the same molecular entity, the magnetic properties can be totally different from the sum of the magnetic properties of each ion surrounded by its nearest neighbors. These new properties depend on the nature and the magnitude of the interaction between the metal ions through the bridging ligands. If both ions have an unpaired electron (e.g. Cu²⁺ ions), then the molecular state of lowest energy is either a spin singlet or a spin triplet. In the former case, the interaction is said to be antiferromagnetic, in the latter case ferromagnetic. The nature and the order of magnitude of the interaction can be engineered by judiciously choosing the interacting metal ions and the bridging and terminal ligands, and, thus, by the symmetry and the delocalization of the orbitals centered on the metal ions and occupied by the unpaired electrons (magnetic orbitals). The first success in this “molecular engineering” of bimetallic compounds was in the synthesis of a Cu²⁺VO²⁺ heterobimetallic complex in which the interaction is purely ferro-magnetic. The same strategy could be utilized for designing molecular ferromagnets, one of the major challenges in the area of molecular materials. Another striking result is the possibility of tuning the magnitude of the interaction through a given bridging network by modifying the nature of the terminal ligands, which, in some way, play the role of “adjusting screws”. By careful selection of the bridging and terminal ligands, a very large antiferro-magnetic interaction can be achieved, even if the metal ions are far away from each other. Some sulfur-containing bridges are especially suitable in this respect.     

乙基纤维素液晶的螺旋性质及影响因素的研究

以乙基纤维素／丙烯酸体系为例，对乙基纤维素液晶的胆甾相性质及其影响因素进行了研究，测定了体系胆甾相结构的螺距。结果表明，乙基纤维素／丙烯酸液晶体的螺旋方向为左旋，随溶液液浓度的增大，胆甾相结构的螺距减小。胆甾相结合的螺距还明显地受到温度，压力、溶剂组成，高分子掺杂等因素的影响。     

Synthesis of ferrocene derivatives exhibiting low-temperature mesomorphism

Novel ferrocenomesogens exhibiting low-temperature mesomorphism have been synthesised from 4-ferrocenylphenol and n-alkoxy naphthoic acid intermediates (n = 4 to 16). The phase behaviour has been investigated in detail by polarising optical microscopy and differential scanning calorimetry.     

不对称大环双核铜(Ⅱ)配合物[Cu2(C23H26Cl2N4O2)](ClO4)2的合成、晶体结构及磁性

大环双核铜(Ⅱ)配合物由N,N′-二甲基-N,N′-二(3-甲酰基-5-氯水杨醛)乙二胺和1,3-丙二胺,与铜(Ⅱ)反应形成的,经过X-射线单晶衍射结果表明：a=0.871 05(16) nm,b=0.957 78(18) nm,c=1.810 4(3) nm,β=100.761(18)°,V=1.483 8(5) nm³,Z=2,D_c=1.762 Mg·m^-3,μ=1.85 mm^-1,F(000)=796,and final R₁=0.061,wR₂=0.126。晶体结构表明：两个铜离子位于双核大环中间,与大环的胺、亚胺以及酚羟基的氧进行配位。磁性结果表明配合物为反铁磁性。