Synthesis and characterization of thiophene-containing liquid crystals |
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Authors: | Long-Hai Wu Yen-Chih Wang Chain-Shu Hsu |
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Institution: | Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan 30050, PR China |
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Abstract: | Six series of liquid crystal materials containing a 2,5-disubstituted thiophene unit were synthesized. The liquid crystal compounds obtained were characterized by NMR, differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction techniques. The properties of liquid crystalline phases were investigated as a function of spacer units, number of aromatic core rings and different terminal moieties. Cyano, methoxy and iodo groups were used as terminal groups. It is found that: (i) compounds having one thiophene ring and one phenyl ring connected by an ester group, with a length/breadth value of 2.1, exhibit no mesophase, while other compounds containing two biphenyl rings, with a length/breadth ratio of 2.7, show mesophases; (ii) the polarity of terminal groups and the flexible spacer length significantly affect the thermal behaviour of these compounds; (iii) the nematic transition range of cyano-containing compounds decreases with increasing length of the flexible spacer, and long alkenyloxy chains tend to facilitate the formation of the smectic phase and suppress the nematic phase in all the mesogenic compounds synthesized. |
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Keywords: | ferroelectric liquid crystal Goldstone mode dye dispersion spontaneous polarisation guest–host effect response time |
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