Liquid Crystalline Complexes Research Articles

Liquid crystalline N-aryl-β-aminovinyl ketones and their complexes with lanthanides

Liquid crystalline lanthanide complexes with N-aryl-substituted β-aminovinyl ketones were synthesized for the first time. The complexes give rise to smectic A mesophase and are stable only in the solid state; in going to solution, they dissociate with formation of the initial ligand.

The EB-DNA Liquid Crystalline Complex with High Concentration of Mg2+

The effects of ethidium bromide (EB) on the DNA cholesteric phase in the high ionic strength of Mg2+ were investigated by polarized optical microscopy (POM), 31P and 23Na nuclear magnetic resonance (NMR). It was found that the cholesteric pitch in the EB-DNA cholesteric phase is obviously smaller than that in the EB-free DNA cholesteric solutions with the same ionic strength of Mg2+ at room temperature. The fraction of liquid crystal phase in both the EB-free and the EB-DNA solutions is decreased with increasing the Mg2+ concentration. But the fraction of liquid crystal phase in the EB-DNA solutions is higher than that in the EB-free DNA solutions at the same Mg2+ concentration, which is attributed to the change of the surface charge distribution on the DNA chains and the stiffness of DNA due to intercalation of EB. The results of the 23Na NMR experiments suggested that the intercalation of EB results in the changes of the ionic environment close to the DNA chains, by which the liquid crystal behavior of DNA is affected.

New metallomesogens with enaminoketonato ligands

Several metallomesogens based on enaminoketonato ligands have been prepared. 1‐Amino‐1‐(4′‐butoxy‐4‐biphenyl)oct‐1‐en‐3‐one was synthesized by heterocycle hydrogenolysis in 3‐(4′‐butoxy‐4‐biphenyl)‐5‐amyl‐isoxazole. Liquid crystalline complexes were obtained by reaction of this enaminoketone with nickel(II) or copper(II) acetates. Hydrogenolysis of the heterocycle in 3‐(4‐hydroxyphenyl)‐5‐amylisoxazole led to 1‐amino‐1‐(4‐hydroxyphenyl)oct‐1‐en‐3‐one. The corresponding copper(II) enaminoketonate was then obtained. The subsequent reaction of this compound with 4‐alkoxy‐benzoic acid chlorides gave liquid crystalline complexes with ester bridges in the core. A nematic phase was observed for all the synthesized metallomesogens. The bridging group influence on melting points, mesophase ranges and thermal stability of copper(II)complexes is discussed.

Mesomorphism of ionic allylpalladium(ii) complexes containing pzR2py as ligands and [BF4]−, [PF6]−or [CF3SO3]−as counteranions

The synthesis and thermal behaviour is reported of some ionic liquid-crystalline complexes formed when a mesogenic, two-chained, pyrazolylpyridine ligand is bound to a eta3-allylpalladium(II) fragment. The phase behaviour of the complexes is dominated by the formation of the SmA phase and, while the stability of the crystal phase appears to be controlled by intermolecular solid-state interactions, the stability of the liquid crystal phases is controlled by the length of the ligand alkoxy chains. Some of the complexes also show a complex polymorphism leading to the observation of double-melting behaviour.

Design of High Coordination Number Metallomesogens by Decoupling of the Complex-Forming and Mesogenic Groups: Nematic and Lamello-Columnar Mesophases

Liquid-crystalline complexes of rhenium(I), yttrium(III), lanthanum(III), neodymium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) were obtained by coupling mesogenic 4-cyanobiphenyl groups via a long alkyl spacer to a substituted imidazo[4,5-f]-1,10-phenanthroline, which acts as the coordinating group. In the case of the rare-earth complexes, 2-thenoyltrifluoroacetonate was used as the coligand. The rhenium(I) complexes contain the bromotricarbonylrhenium(I) moiety. All the rare-earth complexes exhibit a nematic phase, whereas the rhenium(I) complexes and the imidazole-bearing phenanthroline derivatives show a nematic or a lamellar columnar phase, depending on the number of attached mesogenic groups. The phase structures of the lamellar columnar phases are discussed and described on the basis of both X-ray diffraction data and dynamic molecular modeling. The lanthanide complexes are highly luminescent in the solid phase and as a solution in a nematic liquid-crystal host (5CB). The ap...

Liquid crystalline complexes of an azo‐containing surfactomesogen with oppositely charged polyelectrolytes

AbstractA triethyl‐ammonium functionalized 4‐nitro‐4′‐alkoxy azobenzene mesogen with a 10‐carbon spacer (azo10Q, a ‘surfactomesogen’) was complexed in equimolar proportions to a variety of oppositely charged polyelectrolytes, and studied by differential scanning calorimetry (DSC), polarizing optical microscopy, and X‐ray diffraction. The complexation generates a single‐layer smectic A mesophase over a very wide temperature range from a surfactomesogen that, alone, melts directly to the isotropic phase. The clearing temperatures, ranging from 130 to 190 °C and generally higher than the melting point of azo10Q, are dependent on the nature of the polyelectrolyte as well as its molecular weight. In contrast, a prominent glass transition near ambient temperature appears to be independent of molecular weight, but varies somewhat with the type of polyelectrolyte. A second Tg‐like transition of much lower intensity is detectable at higher temperatures (generally above 100 °C), and, with literature support, is tentatively attributed to nanophase separation involving sublayer planes in the lamellar packing structure. A series of nonequimolar complexes was also investigated, and it was found that, with decreasing azo10Q content, the clearing temperature viewed by DSC decreases rapidly in intensity (and somewhat in temperature) and then disappears although birefringence remains, whereas the lower glass transition increases rapidly in temperature to finally merge with the upper one. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3421–3431, 2005

Liquid-Crystalline and Orientation Properties of Lanthanide Complexes with β-Enaminoketone

A series of liquid-crystalline lanthanide complexes with 1-(4-dodecyloxyphenyl)-3-octadecylamino-2-propene-1-one (HL), which is substituted β-enaminoketone, with the composition Ln(HL)3(NO3)3 (Ln = La, Nd, Gd, Tb, Dy, Ho, and Er) is synthesized. For the most part of the synthesized complexes, the magnetic susceptibility anisotropy (Δχmin) is shown to be one to two orders higher than Δχ of the “classical” organic liquid crystals.

Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.

Synthesis and studies of some 4-substituted phenyl-4′-azopyridine-containing hydrogen-bonded supramolecular mesogens

Novel azopyridine-containing supramolecular liquid crystalline (LC) materials built via 1 : 1-heterointermolecular hydrogen bonding between some 4-substituted phenyl-4′-azopyridines and 4-n-alkyloxybenzoic acids are reported. These hydrogen-bonded LC complexes exhibit well defined nematic, smectic A and smectic C phases over wide ranges of temperature depending upon the number of carbon atoms present in the alkyl chains. The formation of pure LC materials on 1 : 1-complexation could be confirmed from the phase diagrams of the binary mixtures, which clearly indicated a melting maximum for the 50 mol% mixture as well as the presence of two eutectic points on either side of this mixture.

Luminescent lanthanide complexes with liquid crystalline properties

Lewis-base adducts of tris(β -diketonato)lanthanide(III) complexes were prepared, where the β -diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β -diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature.

Ion-conductive mechanism in liquid crystalline molecules having polyether segment

A series of liquid crystalline molecules, α,ω-bis{4-[(4′-pentyloxy (or -octyloxy)-4-biphenylyl)-carbonyloxy]phenyl}oligo(oxyethylene)s, was synthesized to prepare oriented oligo(oxyethylene) chains. The complexes with LiCF 3SO 3 spontaneously formed a smectic phase. Since a rigid rod part cannot solubilize the inorganic salts, the oxyethylene moieties form the ion-conductive layers in the smectic phase. The anisotropic ionic conductivity was measured by an impedance analyzer with gold comb-shaped electrode deposited on a glass substrate between Au teeth. The ionic conductivity between the gold teeth increased to 10 −3 S cm −1 at 142 °C, but it dropped considerably to 10 −4 S cm −1 above that temperature. The temperature corresponded to the isotropization point of the complex. Homeotropic orientation of the liquid crystalline complex enables to make a successive ion-conducting pathway, which is effective to obtain higher ionic conductivity. The effect of the added salts on the ionic conductivity was also analyzed. Higher ionic conductivity was obtained when the liquid crystals were complexed with LiCF 3SO 3. There is a suitable ion size for prompt ion migration in the oriented polyether.

Mesomorphism of lanthanide-containing Schiff's base complexes with chloride counterions

Liquid crystalline complexes [Ln(LH)3Cl3] have been synthesized, where Ln is a trivalent lanthanide ion (Pr-Lu, except Pm) and where LH is the Schiff's base ligand N-octadecyl4-tetradecyloxysalicylaldimine. Although the ligand does not exhibit mesomorphism, the complexes do (SmA phase). The mesophase behaviour of these compounds has been investigated by polarizing optical microscopy, differential scanning calorimetry and high temperature X-ray diffraction. The lanthanide complexes have much higher melting and clearing points than comparable complexes with nitrate or dodecyl sulphate counterions. In addition, the transition temperatures are virtually independent of the type of lanthanide ion. This behaviour is opposite to that observed for similar complexes with nitrate counterions [Ln(LH)3(NO3)3]. The differences in temperature dependence can be related to structural differences. Whereas in the nitrate complexes the Schiff's base ligand binds in a zwitterionic form, two-dimensional 1H NMR correlation spectroscopy (COSY) of [Lu(LH)3Cl3] gives an indication that in the chloride complexes, besides coordination via the oxygen of molecules in the zwitterionic form, some of the Schiff's base ligands bind in a bidentate fashion (via the phenolic oxygen and the imine nitrogen).

Liquid crystalline behaviour of hydrogen-bonded complexes of alkoxycinnamic acids with octyloxystilbazole

Hydrogen-bonded liquid crystalline complexes have been obtained through 1:1 (molar ratio) complexation of 4-n-alkoxycinnamic acids (nCNA: n = 4, 8, 10, 12, where n is the number of carbons in the alkyloxy chain) and trans-4-octyloxystilbazole (8Sz). These hydrogen-bonded complexes (nCNA8Sz) form stable mesophases. The mesomorphic range was extended by the mixing of complexes. Hexatic modification of smectic B (SmBh), smectic C (SmC), smectic A (SmA), and nematic mesophases of these complexes were determined by a combination of X-ray diffraction and polarizing optical microscopy. Transitions between the various smectic phases were deduced from the temperature-dependent layer spacing of nCNA8Sz. The layer spacing of these complexes in the SmBh and SmA phases gradually increased with increasing alkoxy chain length. The favouring of smectic phases in these complexes is believed to originate from the increment of polarity of the mesogen by intermolecular H-bonding.

Enhanced conductivity and dielectric absorption in discotic liquid crystalline columnar phases of a vanadyl complex

A liquid crystalline vanadyl complex has been studied by DSC, polarizing optical microscopy, the reversal current technique, X-ray diffraction and frequency domain dielectric spectroscopy. The compound exhibits three columnar phases: rectangular ordered (Colro), rectangular disordered (Colrd), and hexagonal disordered (Colhd), all of which show a dielectric relaxation process at low frequencies. In the Colro low temperature phase this process seems to be connected with a slow relaxation of polarized polymeric chains inside the columns (mHz frequency range). However, in the Colhd high temperature disordered phase this relaxation is faster (Hz range). It is interesting that the liquid crystalline phases studied show enhanced conductivity which changes by four orders of magnitude from 10−9 S m−1 in the orientationally disordered crystal (an ODIC phase) to 10−5 S m−1 in the Colhd high temperature phase. Such a value of the conductivity is typical for semiconducting materials.

Induced Smectic-G Phase through Intermolecular Hydrogen Bonding. Part VI: Thermal and phase Behavior of 2-(4-Decyloxybenzylidene Imino)-5-Chloropyridine (Dacp : Aba) Complexes

A novel series of liquid-crystalline complexes involving intermolecular hydrogen bonding between p - n -alkoxybenzoic acids (ABA) (where alkoxy = propoxy- to decyloxy- and dodecyloxy-) and 2-(4-decyloxybenzylidene imino)-5-chloropyridine (DACP) have been synthesized and their thermal and phase behaviour are studied by Thermal Microscopy (TM) and Differential Scanning Calorimetry (DSC). A detailed IR spectral investigation in solid and solution states confirms the formation of H-bonding between pyridine ring nitrogen and -COOH group of DACP and ABA respectively. Comparative thermal analyses of both free p - n -alkoxybenzoic acids and H-bonded complexes suggest the inducement of smectic-G phase in all the complexes, with a simultaneous quenching of smectic-C phase. The comparative thermal and phase behaviour with analogous series 2-(4-nonyloxybenzylidene imino)-5-chloropyridine : p - n -alkoxybenzoic acids (NACP : ABA) and 2-amino-5-chloropyridine : p - n -alkoxybenzoic acids (ACP : ABA) also imply the stabilization of the induced phase with a wide thermal span.

Lanthanide containing Schiff's base complexes with chloride counter-ions: mesomorphic properties

Liquid crystalline lanthanide complexes (metallomesogens) with chloride counter-ions have been synthesized. The complexes have the stoichiometry [Ln(LH) 3Cl 3], where Ln is a trivalent rare-earth ion (Y, Pr, Sm, Eu–Lu), and LH is the ligand N-octadecyl-4-octyloxysalicylaldimine. Although the Schiff's base ligands do not exhibit mesomorphism, the complexes do (SmA phase). The mesomorphic behaviour of these compounds has been investigated by hot-stage polarized microscopy, differential scanning calorimetry (DSC) and high temperature X-ray diffraction measurements. The stoichiometry of the complexes remains constant throughout the lanthanide series. The complexes have rather high transition temperatures.

Induced Smectic-G Phase through Intermolecular Hydrogen Bonding Part VIII: Phase and Crystallization Behaviours of 2-(p-n-heptyloxybenzyIidene imino)-5-chIoro-pyridine: p-n-alkoxybenzoic acid (HICP:n ABA) Complexes

Abstract New intermolecular H-bonded liquid crystalline complexes, viz., 2-(p-n-heptyloxybenzylidene imi-no)-5-chloro-pyridine:p-/z-alkoxybenzoic acid; (HICP:nABA) (where n denotes the alkoxy carbon num­ bers 3 to 10 and 12) exhibiting smectic-F (n = 12) and smectic-G phases have been synthesized and char­ acterized by Thermal Microscopy and Differential Scanning Calorimetry (DSC). Detailed IR (solid and solution states) analysis confirms the existence of intermolecular H-bonding between the pyridyl nitro­ gen and the COOH group of the p-n-alkoxybenzoic acid moiety. The phase behaviour of the series is discussed in the light of reported data on free p-n-alkoxybenzoic acids. The crystallization kinetics of a representative complex, using the DSC technique, is discussed. The mechanism of the crystal growth of the new crystalline smectic-G phase is computed with the Avrami equation.

Dynamic Behavior of a Hydrogen-Bonded Liquid Crystal Induced by the Orienting Film with a Large Dipole Moment

Poly-(γ-benzyl-L-glutamate) molecules have been bonded covalently to a flat substrate via carbonyl end group to form an aligned dipole layer (CRA film). The authors have evaluated the electric influence of the CRA film on the dynamic change of the hydrogen-bonded liquid crystalline complex of 4-hexyloxybenzoic acid and 4-nonylpyridine (6OBA-9Py) by means of time-resolved infrared spectroscopy. Using the CRA film as an orienting film for 6OBA-9Py, the absorbance change of the complex when burst electric field was applied had many steps in response to the change of its sign. Moreover, the movement of the 6OBA-9Py complex was induced by an external electric field, not only in the direction of the complex long axis but also in that of the complex short axis. This characteristic dynamic behavior of the 6OBA-9Py complex was due to the weak hydrogen bonding.

Phase behaviour of hydrogen-bonded liquid crystalline complexes of alkoxycinnamic acids with 4,4'-bipyridine

The hydrogen-bonded liquid crystalline complexes of 4-n-alkoxycinnamic acids (nCNA: n=4-8, 10, 12, 16, 18, where n is the number of carbons in the alkoxy chain) with 4,4'-bipyridine (BPy) have been prepared and characterized. The existence of smectic C, smectic A, and nematic mesophases of these complexes was demonstrated by a combination of polarized optical microscopy and X-ray diffraction (XRD). In this H-bonded mesogenic structure, nonmesogenic BPy functions as the core unit of the mesogen through the H-bond, as confirmed by infrared spectroscopy and XRD. A general comparison of nCNABPy with the benzoic acid analogues (nOBA)2-BPy, showed that the elongated nCNABPy mesogen behaves as a rod unit and increases the transition temperature. Smectic phases in nCNAs (5≤ n≤ 12) were induced on complexation with BPy. The favouring of smectic phases in these complexes is believed to originate from the increment of polarity of the mesogen by intermolecular H-bonding. With increasing chain length of the nCNABPy complexes the smectic C phase becomes stabilized, like conventional rod-coil molecules.

Mesomorphism of lanthanide-containing Schiff's base complexes with dodecyl sulphate counterions

Liquid crystalline complexes of the formula [Ln(LH)3(DOS)3] have been synthesized, where Ln is a trivalent rare earth-ion (Y, La-Lu, except Pm), LH is the ligand N-octadecyl-4-tetradecyloxysalicylaldimine and DOS is the dodecyl sulphate counterion. Although the Schiff 's base ligands do not exhibit mesomorphism, the complexes do (SmA phase). The mesophase behaviour of these compounds has been investigated by polarizing optical microscopy, differential scanning calorimetry, high temperature X-ray diffraction and thermogravimetric analysis. The stoichiometry of the complexes remains constant throughout the lanthanide series.