Mesogenic heterocyclic pyrazoles,isoxazoles and 1,3,4-oxadiazoles |
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Authors: | Zih-Yang Lei Hsiu-Ming Kuo Chung K Lai |
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Institution: | Department of Chemistry, National Central University, Chung-Li, Taiwan, ROC |
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Abstract: | Three new series of liquid crystals 1-3 derived from heterocyclic pyrazoles, isoxazoles and 1,3,4-oxadiazoles exhibiting smectic A or C phases were reported. Compound 1a exhibited monotropic smectic A phase, while the other two compounds 2-3a were not mesogenic. In contrast, all other compounds 1-3b bearing longer alkoxy chains exhibited smectic X and C phases, which were confirmed by powder XRD diffractometer. The clearing temperatures decreased in the order of compounds 1b > 2b > 3b, in contrast the temperature range of smectic C phases increased in the order of compounds 1b < 2b < 3b. The smectic phases in 1-3b were formed by a monomeric structure, confirmed and consistent with powder X-ray diffraction data. The formation of mesomorphic behavior might be probably attributed to their exocyclic angles and/or H-bonds. All derivatives showed good stabilities at temperature below T = 346 °C on TGA analysis. |
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Keywords: | Mesogens Oxadiazoles Pyrazoles Isoxazole Catenar Calamitic mesophase |
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