Effect of methoxy groups on liquid crystalline and self-assembling properties of 2,7,12-tris(methoxy)-3,8,13-tris(alkoxy)-5,10,15-truxenones

• Published in: Liquid crystals Vol. 48; no. 1; pp. 111 - 120
• Main Authors: Xu, Hong-Tian, Xia, Xue, Yu, Wen-Hao, Feng, Chun, Xiang, Shi-Kai, Wang, Bi-Qin, Zhao, Ke-Qing, Ni, Hai-Liang, Hu, Ping
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 02.01.2021; Taylor & Francis Ltd
• Subjects: Chains; columnar phase; Crystal structure; Crystallinity; discotic liquid crystal; Liquid crystals; Melting point; Melting points; Mesophase; self-assembling; Self-assembly; Temperature; Truxeneone
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2020.1766136

Four truxeneones 6a-d in which three long alkoxy chains and three methoxy groups were C 3 -symmetrically attached to the truxenone core have been synthesised and studied with the aim to study the effect of bulky methoxy substituents on their mesomorphism and self-assembly properties. These four compounds show enantiotropic mesophase and each has a Col h phase over a 135°C temperature range. A comparison of the side chains showed that 6a-d with mixed alkoxy chains display more complex thermotropic behaviour than reported truxenones possessing six identical long alkoxy chains. Although the methoxy groups have almost no effect on their self-assembly in solution due to the staggered face-to-face arrangement of truxenone moieties, it is confirmed that replacement of three long alkoxy chains by methoxy groups may affect the packing of molecules in the crystalline state more than that within the mesophase. The presence of methoxy groups results in lowering of both the clearing point and the temperature range of the Col h phases by maintaining high melting point. Moreover, 6a self-assembles on a solid/liquid interface into a well-ordered two-dimensional architecture which was explored using high-resolution STM that closely resembles to the proposed bulk mesomorphic three-dimensional columnar phase deduced from XRD.