Hexakis(4-iodophenyl)-peri-hexabenzocoronene- A Versatile Building Block for Highly Ordered Discotic Liquid Crystalline Materials

Abstract

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 π−π 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.