Shape and Confinement Effects of Various Terminal Siloxane Groups on Supramolecular Interactions of Hydrogen-Bonded Bent-Core Liquid Crystals

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• 作者：I-Hung Chiang ; Wei-Tsung Chuang ; Chia-Lin Lu ; Ming-Tao Lee ; Hong-Cheu Lin
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：July 14, 2015
• 年：2015
• 卷：27
• 期：13
• 页码：4525-4537
• 全文大小：818K
• ISSN：1520-5002

文摘

To investigate the shape and confinement effects of the terminal siloxane groups on the self-assembled behavior of molecular arrangements in hydrogen-bonded (H-bonded) bent-core complexes, four H-bonded bent-core complexes S1, P1, C4, and P8 with string-, ring-, and cage-like siloxane termini (i.e., linear siloxane unit 鈭扴i鈥揙鈥揝i鈥揙鈥揝i鈥? cyclic siloxane unit (Si鈥揙)₄, and silsesquioxane unit POSS, respectively) were synthesized and investigated. By X-ray diffraction measurements, different types of SmCG (B8) phases and leaning angles were controlled by the shape effect of the string- and cage-like siloxane termini for S1 and P1 (with only one arm of H-bonded bent-core), respectively. In addition, the confinement effect of P1, C4, and P8 (accompanied by increasing the numbers of attached H-bonded bent-core arms) resulted in higher transition temperatures and the diminishing of mesophasic ranges (even the disappearance of mesophase in P8). Moreover, AFM images showed the bilayer smectic CG phases of S1 and P1 were aligned to reveal highly ordered thread-like structures by a DC field. By spontaneous polarization measurements within the mesophasic ranges, S1 and P1 showed ferroelectric transitions but C4 displayed antiferroelectricity. Finally, the electro-optical performance of B8 phases could be optimized through binary mixtures of S1 and P1, and a well aligned modulated ribbon phase could be formed via specific molar ratios of the binary mixtures.