Heterolithic azobenzene-containing supermolecular tripedal liquid crystals self-organizing into highly segregated bilayered smectic phases
作者:Zsuzsanna T. Nagy、Benoît Heinrich、Daniel Guillon、Jaroslaw Tomczyk、Joachim Stumpe、Bertrand Donnio
DOI:10.1039/c2jm33751g
日期:——
Synthesis, self-organization, and optical properties of supermolecular tripedal liquid crystals incorporating various prototypical mesogenic units such as alkoxy-azobenzene (AZB), alkoxy-biphenylene (BPH) or alkoxy-cyanobiphenyl (OCB) derivatives are reported. Different molecular systems were designed in order to sequentially incorporate the smectogenic-like alkoxy-azobenzene-based chromophore within the molecular structure, whose relative proportion is selectively varied by exchanging with the other mesogens. A divergent synthetic mode was elaborated for their synthesis, starting from the regioselective functionalization of the phloroglucinol-based (PG) inner core. This methodology allowed the preparation of several sets of unconventional tripedal oligomers with conjugated heterolithic structures (made of different blocks, e.g. PG6AZBxBPH3−x and PG6AZBxOCB3−x, x = 1 or 2) along the homolithic parents (all identical blocks, e.g. PGzAZB3, z = 6 or 11, z is the number of methylene in the spacer between PG and the protomesogen, PG6BPH3, and PG6OCB3), respectively. Essentially all the synthesized systems behave as thermotropic liquid crystals and show various types of highly segregated multilayered smectic phases, or, in one case, a nematic phase, depending on the nature of the constitutive anisotropic blocks and on the molecular topology (homolithic versus heterolithic, mesogenic ratio x : 3 − x). The effects of these structural modifications on the mesomorphism (mesophase structures, temperature ranges, and thermodynamic stability) have been investigated by differential scanning calorimetry and small-angle X-ray diffraction experiments combined with dilatometric measurements. Models describing the various supramolecular organizations of these tripedes into such multilayered structures are proposed and discussed. Preliminary results of the investigations of their optical properties will also be presented.
超分子三脚架液晶的合成、自组织和光学性质,包含各种典型的介晶单元,如烷氧基偶氮苯(AZB)、烷氧基联苯(BPH)或烷氧基氰基联苯(OCB)衍生物。设计了不同的分子系统,以便依次将类层状烷氧基偶氮苯染料嵌入分子结构中,其相对比例通过与其他介晶交换而选择性变化。为了它们的合成,详细阐述了一种发散合成模式,从基于间苯三酚(PG)内核的区域选择性功能化开始。这种方法允许制备几组非传统的三脚架寡聚物,分别具有共轭异质结构(由不同的块组成,例如PG6AZBxBPH3−x和PG6AZBxOCB3−x,x = 1或2)和同质结构(所有相同的块,例如PGzAZB3,z = 6或11,z是间隔子中亚甲基的数量,位于PG和原介晶之间,PG6BPH3和PG6OCB3)。基本上所有合成的系统都表现为热致液晶,并显示出各种高度分层的多层状层状相,或者在一例中显示出向列相,这取决于组成各向异性块的性质和分子拓扑结构(同质与异质,介晶比x:3 - x)。通过差示扫描量热法和X射线小角衍射实验结合膨胀测量,研究了这些结构变化对介晶化(介相结构、温度范围和热力学稳定性)的影响。提出了描述这些三脚架在多层结构中各种超分子组织的模型并进行了讨论。关于它们光学性质研究的部分初步结果也将呈现。