Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER), Mohali, Sector-81, Knowledge city, Manauli-140306, India.
Org Biomol Chem. 2019 Feb 13;17(7):1947-1954. doi: 10.1039/c8ob01579a.
Liquid crystals (LCs) with photoswitchable groups are very interesting owing to their dual applications. In this regard, we report the synthesis of long chain alkoxy azobenzene incorporated benzenetricarboxamides 7a-c based room temperature columnar LCs. Apart from the light induced isomerization in the solution phase, the salient feature of these systems is the reversible photoisomerization even in the bulk state with perpetual columnar self-assembly at room temperature. Based on the observation of mesomorphic textures under polarised optical microscopy (POM) and grazing incidence small/wide angle X-ray scattering (GISAXS/GIWAXS) studies, the columnar assembly was found to be stable upon photoisomerization. However, subtle changes in height profile have been observed in AFM measurements after photoswitching. Interestingly, a temperature dependent change between rectangular and hexagonal mesophases in 7a has been observed. Upon extending the alkoxy chain length, only the hexagonal mesophase was observed. For comparison, the corresponding N-methylated derivative of 7a has also been synthesized. Despite the better photoswitching behaviour, due to the lack of planarity and H-bonding, 8a did not show any columnar mesophase.
具有光致变色基团的液晶因其双重应用而非常有趣。在这方面，我们报告了长链烷氧基偶氮苯掺入苯三甲酰亚胺 7a-c 的合成，这些化合物是基于室温柱状液晶。除了在溶液相中光诱导的异构化外，这些体系的突出特点是即使在块状状态下也能进行可逆光致异构化，并且在室温下仍具有永久性柱状自组装。根据偏光显微镜（POM）和掠入射小/广角 X 射线散射（GISAXS/GIWAXS）研究中介观织构的观察，发现光致异构化后柱状组装稳定。然而，在光致切换后 AFM 测量中观察到高度轮廓的细微变化。有趣的是，在 7a 中观察到了温度依赖性的矩形和六方相之间的变化。随着烷氧基链长的延长，仅观察到六方相。为了进行比较，还合成了 7a 的相应 N-甲基化衍生物。尽管 8a 的光致变色行为更好，但由于缺乏平面性和氢键，它没有显示出任何柱状介相。
