Modification of the pitch of chiral nematic liquid crystals by means of photoisomerization of chiral dopants

Autor:	Johan Lub, Peter Van De Witte, Juan Carlos Galan
Rok vydání:	1998
Předmět:	Materials science Photoisomerization Dopant General Chemistry Condensed Matter Physics Photochemistry Viewing angle Menthone chemistry.chemical_compound chemistry Liquid crystal Copolymer Organic chemistry General Materials Science Irradiation Isomerization
Zdroj:	Liquid Crystals. 24:819-827
ISSN:	1366-5855 0267-8292
DOI:	10.1080/026782998206632
Popis:	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 ...
Databáze:	OpenAIRE
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