Synthesis and properties of new materials with banana-shaped achiral cores and chiral end groups |
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Authors: | Chong-Kwang Lee Corresponding author Soon-Sik Kwon Tae-Sung Kim E-Joon Choi Sung-Tae Shin Wang-Cheol Zin |
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Institution: | 1. Dept. of Chemistry , Gyeongsang National University , Chinju 660-701, Korea;2. Dept. of Polymer Science and Engineering , Kumho National University of Technology , Kumi 730-701, Korea;3. Department of Physics , Korea University , Chungnam 339-700, Korea;4. Dept. of Materials Science and Engineering , Pohang University of Science and Technology , Pohang 790-784, Korea |
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Abstract: | New chiral bent-core mesogens, derivatives of 1,3-phenylene bis4-(alkanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=F, Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X-ray diffractometry in the small and wide angle regions. The presence of chiral tails at the terminals of side wings in the bent-core molecules induced a decrease in transition temperature and formation of the switchable SmC* phase in the melt. In addition, the introduction of a lateral halogen substituent in the Schiff's base moiety prevented the regular stacking of the molecules, resulting in the formation of very complex optical textures. The smectic phase with F-substituted PBFDOB and Cl-substituted PBCDOB showed layer spacings of 39 and 38.5?Å, respectively, corresponding to the end-to-end distance of molecules with a bent conformation. Significantly, the smectic phases of PBFDOB and PBCDOB exhibited a period of 179.5 and 131?Å, respectively, compatible with a helical structure with periodicity about 4.6 and 3.4 times the layer spacings. |
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Keywords: | high birefringence fluorinated terphenyl liquid crystals vertical alignment response time |
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