New SmCG phases in a hydrogen-bonded bent-core liquid crystal featuring a branched siloxane terminal group.
New SmCG phases in a hydrogen-bonded bent-core liquid crystal featuring a branched siloxane terminal group.
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氢键弯核液晶中的新型 SmCG 相，具有支化硅氧烷端基。
DOI：
10.1021/ja205550b
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发表时间：
2011
影响因子：
15
通讯作者：
Hong‐Cheu Lin
中科院分区：
文献类型：
--
作者：
Wei;Wei‐Tsung Chuang;U. Jeng;H. Sheu;Hong‐Cheu Lin
在本研究中，我们合成了三种类似的弯核分子，即具有支化硅氧烷单元（分别为H-SiO和C-SiO）的氢键配合物和共价键化合物以及具有烷基单元（H-Alk）的氢键配合物，并研究了氢键和支化硅氧烷末端单元对其介晶性质的影响。共价键化合物C-SiO和氢键配合物H-Alk表现出典型的SmCP相；相比之下，氢键复合物H-SiO表现出一系列具有高度有序层结构的一般倾斜近晶（SmCG）相（即冷却后的SmC̃G(2)P(F)-USmCG(2)P(A)-SmCG(2)P(F)-SmCGP(F)）。在 SmCG 型相变过程中，随着氢键强度随着温度的降低而增加，二维调制的带状结构通过起伏层转变为高度有序的层。当 SmCG 域在直流电场下排列时，倾斜角从约逐渐减小。 60°至50°（同时倾斜角保持在约31°）可以通过原位广角X射线散射（WAXS）来确定。结合傅里叶变换红外和拉曼光谱数据，我们的结果表明倾斜角的变化是由氢键竞争和氢键复合物H-SiO双层结构内硅氧烷单元的微观偏析控制的。此外，H-SiO 的 SmCG 型相中的切换电流响应证明了铁电-（反铁电）-铁电转变，表明极性切换是通过围绕 H-SiO 长轴的集体旋转而发生的。因此，通过弯核氢键液晶复合物H-SiO中的氢键和支化末端硅氧烷单元的作用，诱导出具有一系列高度有序的二维结构的新型SmCG相。
In this study, we synthesized three analogous bent-core molecules, a hydrogen-bonded complex and a covalent-bonded compound with branched siloxane units (H-SiO and C-SiO, respectively) and a hydrogen-bonded complex with an alkyl unit (H-Alk), and investigated the effects of the hydrogen bonding and branched siloxane terminal units on their mesomorphic properties. The covalent-bonded compound C-SiO and the hydrogen-bonded complex H-Alk exhibited typical SmCP phases; in contrast, the hydrogen-bonded complex H-SiO exhibited a series of general tilt smectic (SmCG) phases with highly ordered layer structures (i.e., SmC̃G(2)P(F)-USmCG(2)P(A)-SmCG(2)P(F)-SmCGP(F) upon cooling). During the SmCG-type phase transition process, a 2D-modulated ribbon structure transferred into highly ordered layers via undulated layers, as the hydrogen-bonding strength increased with reduced temperatures. As the SmCG domains were aligned under dc electric fields, a gradual decrease in the leaning angle from ca. 60° to 50° (while the tilt angle kept at ca. 31°) could be determined by in situ wide-angle X-ray scattering (WAXS). Combined with Fourier transform infrared and Raman spectroscopic data, our results suggest that the change in the leaning angle was governed by the competition of the hydrogen bonds and microsegregation of siloxane units within the bilayer structure of the hydrogen-bonded complex H-SiO. In addition, the ferroelectric-(antiferroelectric)-ferroelectric transitions proven by the switching current responses in the SmCG-type phases of H-SiO reveal that the polar switching occurred through collective rotations around the long axis of H-SiO. Therefore, novel SmCG phases with a series of highly ordered 2D-structures were induced by the effects of the hydrogen bonding and branched terminal siloxane unit in the bent-core hydrogen-bonded LC complex H-SiO.