Spacer parity dependence of photoinduced effects in liquid-crystalline dimers

• Published in: Journal of applied physics 2002-07, Vol.92 (2), p.838-841
• Main Authors: Prasad, S. Krishna, Sandhya, K. L., Nair, Geetha G., Hiremath, Uma S., Yelamaggad, C. V.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.1488244

Liquid crystals composed of photoactive groups like azobenzene are promising materials for optical switching and image storage applications. When exposed to ultraviolet radiation, such materials are known to induce a transition from a liquid-crystalline nematic phase, in which the azo molecules are in the trans form to an isotropic liquid phase when the azo molecules take the cis form. We report the observation of the influence of the parity and length of the flexible spacer of photoactive liquid-crystalline dimers in a guest host system on the photoinduced nematic-isotropic transition. A remarkable feature observed is that in this system, in which the guest dimers are present only in a small concentration (4.8 weight %) the odd–even parity of the spacer results in a striking alternation of the magnitude of the photoinduced shift in the nematic-isotropic transition temperature. Further, it is demonstrated that the shape of the photoactive molecule in its all-trans configuration can be used as a convenient tool to control the photoinduced shift in the nematic-isotropic transition temperature.