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Smectic Mesophase (smectic + mesophase)
Selected AbstractsDesign of Neutral Metallomesogens from 5,5-Dimethyldipyrromethane: Metal Ion Mediated Control of Folding and Hairpin StructuresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2008Kelly A. Ames Abstract New ligands derived from 5,5-dimethyldipyrromethane and their corresponding neutral complexes with ZnII and PdII are described. The ligands incorporate either a hexacatenar [H2(1n), n = 1, 10, 12, 14 and 16], tetracatenar [H2(2n), n = 1 and 16] or an extended dicatenar structure [H2(3n), n = 1and 16]. Single-crystal X-ray structure determinations of [Zn2(11)2] and [Zn2(31)2] confirm a distorted tetrahedral geometry at ZnII to afford double-stranded helical structures, while the PdII species [Pd(31)] shows a distorted square-planar geometry with the ligand adopting an alternative hairpin conformation. The metal-free hexacatenar ligands H2(1n) (n = 10, 12, 14, 16) and the corresponding complexes [Zn2(116)2] and [Pd(1n)] (n = 12, 14, 16) are not mesomorphic. However, the tetracatenar complex [Zn2(216)2] generates a smectic mesophase, as confirmed by X-ray diffraction, while [Pd(216)] and the metal-free ligand H2(216) show no mesomorphic behaviour. Two of the extended dicatenar compounds, H2(316) and [Zn2(316)2] are non-mesomorphic, while [Pd(316)] displays a smectic A phase.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] High Carrier Mobility up to 0.1,cm2,V,1,s,1 at Ambient Temperatures in Thiophene-Based Smectic Liquid Crystals,ADVANCED MATERIALS, Issue 5 2005M. Funahashi The synthesis and carrier-transport properties of oligothiophene liquid-crystalline semiconductors are reported. An asymmetrically substituted terthiophene and quaterthiophene give rise to a highly ordered smectic mesophase (see Figure) with an excellent carrier mobility of up to 0.1, cm2,V,1,s,1 over a wide mesophase temperature range, including ambient temperatures. This mobility is comparable to that of organic polycrystals. [source] Synchrotron X-ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p,-bibenzoate)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2003Ernesto Pérez Abstract Time-resolved synchrotron X-ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p,-bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110,°C. Moreover, the annealing of PDEB at temperatures above Tg for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained. Scattering profiles corresponding to sample PDEB85 in a melting experiment. [source] 4,-[2-(2-Ethoxyethoxy)ethoxy]biphenyl-4-carboxylic acid: correlation between its crystalline and smectic phasesACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Rosana S. Montani The crystal structure of the dimeric title compound, C19H22O5, is dominated by a head-to-head hydrogen-bonding interaction between centrosymmetrically related carboxyl groups in each monomer. The result is a dimeric axis of unusual length (ca 34,Å), but still shorter than what could be expected for a fully extended chain, owing to two turning points in the oligoethoxy ends. This allows for an explanation of the structure of the smectic mesophase exhibited by this compound and at the same time fully validates former geometric estimations based on PM3 calculations. [source] Imidazolium based ionic liquid crystals: structure, photophysical and thermal behaviour of [Cnmim]Br·xH2O (n = 12, 14; x=0, 1)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2008A. Getsis Abstract The long chain imidazolium halides [Cnmim]Br·xH2O (n = 10, 12; x = 0, 1) have been synthesized and their structural and thermal behaviour together with their photophysical properties characterized. X-ray structure analyses of the monohydrates ([C12mim]Br·H2O: triclinic, P1, no. 2, Z = 2, Pearson code aP112, a = 550.0(5) pm, b = 779.4(5) pm, c = 2296.1(5) pm, , = 81.89(5)°, , = 83.76(5)°, , = 78.102(5)°, 3523 unique reflections with Io > 2,(Io), R1 = 0.0263, wR2 = 0.0652, GooF = 1.037, T = 263(2) K; [C14mim]Br,H2O: triclinic, P1, no. 2, Z = 12, Pearson code aP11, a = 549.86(8) pm, 782.09(13) pm, c = 2511.3(4) pm, , = 94.86(2)°, , = 94.39(2)°, , = 101.83(2)°, 2063 unique reflections with Io > 2,(Io), R1 = 0.0429, wR2 = 0.0690, GooF = 0.770, T = 293(2) K) show for both compounds similar bilayered structures. Sheets composed of hydrophilic structure regions constituted by positively charged imidazolium head groups, bromide anions and hydrogen bonded water alternate with hydrophobic areas formed by interdigitated long alkyl chains belonging to imidazolium cations with different orientation. Combined differential scanning calorimetry and polarizing optical microscopy shows that the monohydrates as well as the anhydrous imidazolium salts are thermotropic liquid crystals which adopt smectic mesophases. The mesophase region is larger in case of the monohydrates when compared to the anhydrous compounds indicating that water obviously stabilizes the mesophase. All compounds show an intense whitish photoluminescence with short lived (1,,1,*) and long lived (1,,3,*) transitions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of Novel Chiral Ionic Liquids and Their Phase Behavior in Mixtures with Smectic and Nematic Liquid CrystalsHELVETICA CHIMICA ACTA, Issue 11 2004Martin Tosoni Alkylation of 1-alkyl-1H -imidazoles 2a,f with citronellyl bromide 1b opens access to chiral 1H -imidazolium bromides 3a,f (Scheme,1). A similar strategy yielded the chiral pyridinium ionic liquid 6 (Scheme,2). Dialkylation of 1H -imidazole (7) gave the C2 -symmetric 1,3-dicitronellyl-1H -imidazolium bromide (8) (Scheme,3). Differential scanning calorimetry and optical polarizing microscopy revealed smectic mesophases for 1-citronellyl-3-tetradecy-1H -limidazolium bromide (3e) and 1-citronellylpyridinium bromide (6) (Table). In binary mixtures with smectic and nematic liquid crystals 9 and 10, 1-citronellyl-3-methyl-1H -imidazolium bromide (3a) behaved differently. Increasing quantities of 3a cause a decrease of the smectic-phase width for the mixture 3a/9 (Fig.,3), whereas the phase width of the nematic phase for 3a/10 remained nearly constant (Fig.,4). [source] Liquid-crystalline thermosets by the curing of dimeric liquid-crystalline epoxyimine monomers with 2,4-toluene diisocyanateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2003David Ribera Abstract We studied the curing processes of several series of dimeric liquid-crystalline epoxyimine monomers with 2,4-toluene diisocyanate (TDI) alone or with added catalytic proportions of 4-(N,N -dimethylamino)pyridine. We obtained isotropic materials or liquid-crystalline thermosets with different degrees of order, which depended on the structures of the monomers. To fix ordered networks, we had to do the curing in two steps when TDI was used alone as the curing agent. However, when a tertiary amine was added in catalytic proportions, the ordered networks were fixed in just one step. In this way, we were able to fix both nematic and smectic mesophases. The significance of the polarization of the mesogen for obtaining liquid-crystalline thermosets was demonstrated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2521,2530, 2003 [source] Microwave-assisted Synthesis, Structure, and Tunable Liquid-Crystal Properties of 2,5-Diaryl-1,3,4-Thiadiazole Derivatives through Peripheral n -Alkoxy ChainsCHEMISTRY - AN ASIAN JOURNAL, Issue 7 2009Jie Han Dr. Abstract Chain change: Variations in the position, number, and chain length of the n -alkoxy chains readily tune the liquid-crystalline properties of 2,5-diaryl-1,3,4-thiadiazole derivatives from smectic to hexagonal columnar mesophases at room temperature. The calamitic S-heterocyclic compounds show electrical conductivity in both solid and liquid-crystal states. A series of substituted 2,5-diaryl-1,3,4-thiadiazole derivatives are prepared by microwave-assisted synthesis in the absence of an organic solvent. All derivatives are well characterized by 1H and 13C,NMR, MS, and elemental analyses. The X-ray crystal structure of 2,5-di-(4-decyloxyphenyl)-1,3,4-thiadiazole reveals the tilt lamellar arrangement of rod-shaped molecules, which are stabilized by a variety of weak non-covalent interactions. The liquid crystalline properties are studied by polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), and in,situ variable temperature X-ray diffraction (VTXRD). By variations in the peripheral n -alkoxy chains, the calamitic mesogens exhibit enantiotropic smectic (SmC and/or SmA) mesophases with wide mesomorphic temperature ranges, whilst the disc-like mesogens form hexagonal columnar mesophase (Colh) at room temperature. The bulk electrical conductivity values of the smectic mesophases of 1,3 are in the range of 10,3,10,4 S,cm,1, which are slightly higher than that of their solid films. In contrast, the solid film made from 2,5-di-(3,4,5-trioctyloxyphenyl)-1,3,4-thiadiazole shows poor conductivity (2×10,7,S,cm,1). [source] | |||||||||||||