Wu Jishan, Watson Mark D, Zhang Li, Wang Zhaohui, Müllen Klaus
Max-Planck Institute for Polymer Research, Ackermannweg 10, D-55128, Mainz, Germany.
J Am Chem Soc. 2004 Jan 14;126(1):177-86. doi: 10.1021/ja037519q.
Hexakis (4-iodophenyl)-peri-hexabenzocoronene (5), a novel functionalizable mesogenic building block, was prepared by rational multistep synthesis. Although sparingly soluble in common solvents, it can be obtained in pure form and then functionalized via Hagihara-Sonogashira coupling to give a series of highly ordered columnar liquid crystalline molecules 14a-c. The total synthesis involves five 6-fold transformations, all in excellent to near quantitative isolated yields. Their thermotropic liquid crystalline behavior was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). Compared to the normal alkyl-subsituted hexabenzocoronenes (HBCs), 14a-c exhibit more highly ordered columnar mesophases, including three-dimensionally ordered superstructures (helical columnar mesophase). These could arise from additional intracolumnar pi-pi interactions between, and space-filling requirements introduced by, the rigid-rod side groups. Atomic force microscopy (AFM) revealed self-assembled bundles of columnar aggregates in spin-coated films and isolated several-micron-long nanoribbons composed of a defined number of columns in drop cast films.
六（4-碘苯基）-周-六苯并蔻（5）是一种新型的可功能化介晶结构单元，通过合理的多步合成法制备而成。尽管它在常见溶剂中的溶解度很小，但可以以纯形式获得，然后通过萩原-园田偶联进行功能化，得到一系列高度有序的柱状液晶分子14a - c。全合成涉及五次六重转化，所有反应的分离产率均优异或接近定量。通过差示扫描量热法（DSC）、偏光显微镜（POM）和广角X射线衍射（WAXD）研究了它们的热致液晶行为。与普通烷基取代的六苯并蔻（HBCs）相比，14a - c表现出更高有序的柱状中间相，包括三维有序的超结构（螺旋柱状中间相）。这些可能源于刚性棒状侧基之间额外的柱内π-π相互作用以及引入的空间填充要求。原子力显微镜（AFM）揭示了旋涂膜中柱状聚集体的自组装束，并在滴铸膜中分离出由一定数量的柱组成的几微米长的纳米带。
