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Articles by Ute Baumeister
Total Records ( 3 ) for Ute Baumeister
  Akira Moria , Tomohiko Itoh , Hisashi Taya , Kanji Kubo , Seiji Ujiie , Ute Baumeister , Siegmar Diel and Carsten Tschierske
  Mesomorphic properties of three-ring systems such as 2,5-dibenzoyloxytropones, 5-benzoylamino-2-benzoyloxytropones and 2,5-dibenzoylaminotropones with 4-alkoxy, 3,4-dialkoxy, and 3,4,5-trialkoxy groups on the benzoyl groups were investigated together with those of the corresponding benzenoids. Derivatives with two monoalkoxybenzoyl groups showed nematic and smectic A and C phases. Troponoid tetracatenars with two dialkoxybenzoyl groups had hexagonal columnar phases except for troponoids with two ester-connecting groups, whereas the corresponding benzenoids with two dialkoxybenzoyl groups were non-mesomorphic. All troponoid hexacatenars with two trialkoxybenzoyl groups formed hexagonal columnar phases. With the exception of benzenoid hexacatenars with two ester-connecting groups, the benzenoid hexacatenars showed hexagonal and tetragonal columnar phases. These mesomorphic properties were discussed from the standpoint of the difference of the core structure and the connecting group, where the amide-connecting group played a role to induce and enhance mesomorphic properties through hydrogen bonding.
  Maria Gabriela Tamba , Ute Baumeister , Gerhard Pelzl and Wolfgang Weissflog
  A five-ring bent-core unit and a phenyl benzoate moiety are linked together by means of a flexible spacer. Starting from dimers having different length of the aliphatic parts, that is the terminal alkyloxy chains and the spacer, the direction of each of the four ester connecting groups in the bent-core unit is reversed step by step. In this way thermodynamically stable polar and non-polar mesophases in unusual sequences could be obtained. For instance, a SmCsPAF-SmCs´PAF transition and the existence of two nematic phases (N, NX) have been observed. The nematic phases of the banana-calamitic dimers exhibit unusual properties comparable to those of the nematic phases reported for some monomeric bent-core mesogens. The electric field-induced enhancement of the SmCP-SmA transition temperature of one compound proves the existence of polar clusters already in the non-polar SmA phase.
  Maria-Gabriela Tamba , Alexey Bobrovsky , Valery Shibaev , Gerhard Pelzl , Ute Baumeister and Wolfgang Weissflog
  Azobenzene functionalised banana−calamitic dimers and a novel type of banana−calamitic−banana trimers have been synthesised. Their thermotropic behaviour and the structure of the mesophases have been characterised by differential scanning calorimetry, polarising optical microscopy and X-ray diffractions measurements. Electro-optical studies evidence the polar properties of the smectic phases. A rare anticlinic−synclinic smectic CP (SmCP) phase transition could be proven for two of the twins upon cooling without an electric field although the molecules are not optically active. Remarkably, the phase sequence SmCa−SmCs has been observed upon cooling, the inverse sequence to that reported for non-chiral compounds up to now. A comparative study of the photochemical properties of dilute solutions and of thin films of two compounds has been performed. Irradiation with polarised ultra-violet (365 nm) and visible light (473 nm) induces a photo-orientation process of the chromophores in a direction perpendicular to the polarisation plane of the exciting light. For a trimeric compound bearing an azobenzene bridge between both bent-core mesogenic units this process is associated with cycles of the EZE isomerisation of the azobenzene groups followed by rotational diffusion of molecules in the films. For a bis(azobenzene) containing dimer the EZ isomerisation in films is strongly suppressed and the photo-induced orientation has a rotational diffusion mechanism.
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