Reversible Isothermal Twist–Bend Nematic–Nematic Phase Transition Driven by the Photoisomerization of an Azobenzene-Based Nonsymmetric Liquid Crystal Dimer

详细信息    查看全文

• 作者：Daniel A. Paterson ; Jie Xiang ; Gautam Singh ; Rebecca Walker ; Deña M. Agra-Kooijman ; Alfonso Martı́nez-Felipe ; Min Gao ; John M. D. Storey ; Satyendra Kumar ; Oleg D. Lavrentovich ; Corrie T. Imrie
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：April 27, 2016
• 年：2016
• 卷：138
• 期：16
• 页码：5283-5289
• 全文大小：494K
• 年卷期：0
• ISSN：1520-5126

文摘

The liquid crystal nonsymmetric dimer, 1-(4-butoxyazobenzene-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl) hexane (CB6OABOBu), shows enantiotropic twist–bend nematic, N_TB, and nematic, N, phases. The N_TB phase has been confirmed using polarized light microscopy, freeze fracture transmission electron microscopy, and X-ray diffraction. The helicoidal pitch in the N_TB phase is 18 nm. The N_TB–N (T_NTBN) and N–I (T_NI) transition temperatures are reduced upon UV light irradiation, with the reduction in T_NTBN being much larger than that in T_NI. An isothermal, reversible N_TB–N transition may be driven photochemically. These observations are attributed to a trans–cis photoisomerization of the azobenzene fragment on UV irradiation, with the cis isomers stabilizing the standard nematic phase and the trans isomers stabilizing the N_TB phase. The dramatic changes in T_NTBN provide evidence that the transition between the normal nematic and twist–bend nematic with spontaneous breaking of chiral symmetry is crucially dependent on the shape of molecular dimers, which changes greatly during the trans–cis isomerization.