2018, Vol.91, No.11
Optical Switching between Liquid-Crystalline Assemblies with Different Structural Symmetries and Molecular Orders
2Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
Optical switching between one-dimensionally ordered layered smectic C (SmC) and three-dimensionally periodic bicontinuous cubic (Cubbi) liquid-crystalline (LC) phases is a fascinating challenge because of the dramatic changes of structural symmetries and orders as well as physical properties. In this work, we have developed a new light-driven Cubbi phase system consisting of 4′-n-hexadecyloxy-3′-cyanobiphenyl-4-carboxylic acid (ACBC-16) and a structurally analogous azo compound (Azo-2). The employment of the CN side-group in the host compound brought about outstanding responsiveness under ultraviolet (UV) light in the mixtures containing 11 and 19 mol % Azo-2, leading to a UV response time of ∼5 s and excellent repeatability of on-off switching for the conversion between the two LC phases. The modification also enabled us to quantitatively analyze the mechanism of the light-induced transformation between the two LC phases. The evaluation revealed that the presence of ∼4% of bent molecules in the system under UV light destabilizes the SmC layered structure originally constructed by rod-shaped molecules, causing formation of the Cubbi phase at temperatures 10–35 K below the temperature range of the thermally-stable Cubbi phase.