Modification of the pitch of chiral nematic liquid crystals by means of photoisomerization of chiral dopants
作者:
PETER VAN DE WITTE,
JUAN CARLOS GALAN,
JOHAN LUB,
期刊:
Liquid Crystals
(Taylor Available online 1998)
卷期:
Volume 24,
issue 6
页码: 819-827
ISSN:0267-8292
年代: 1998
DOI:10.1080/026782998206632
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
New photoisomerizable chiral dopants have been studied. The dopants used were menthone derivatives, a chiral stilbene derivative and a nematic copolymer of a menthone derivative and a benzoyloxybenzonitrile derivative. NMR, HPLC and UV results showed that the E-Z-isomerization of all the compounds indicated proceeded rapidly upon UV exposure, without the formation of undesired by-products. Isomerization of the menthone derivatives, including the copolymer, induced a substantial decrease in the helical twisting power. The changes in helical twisting power induced by the isomerization of the chiral stilbene derivative were limited to a factor of 2. In mixtures of the photoisomerizable dopants with commercial dopants of opposite twisting senses and a nematic host mixture, the sign of the twisting sense could be reversed by illuminating the mixture with UV light. The viewing angle dependence of irradiated regions of a 90 -twisted nematic cell was rotated 90 with respect to the viewing angle dependence of the non-irradiated regions. It is expected that this approach may be useful in the preparation of dual domain TN cells with a reduced viewing angle dependence.
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