Columnar liquid crystalline assembly of doubly discotic supermolecules based on tetra-triphenylene-substituted phthalocyanine

Abstract

A series of doubly discotic supermolecules with four triphenylene (Tp) mesogens attached to a phthalocyanine (Pc) core via flexible alkyl spacers were designed and synthesized. The samples were denoted as Pc(Tp)4. Two alkyl chain lengths (C5 and C12) in the Tp arms and two spacer lengths (C6 and C10) were used to study columnar liquid crystalline (LC) self-assemblies in Pc(Tp)4 samples. The mesophase morphology was studied by polarized light microscopy and X-ray diffraction techniques. When the spacer length was relatively long (C10), a normal hexagonal columnar structure with the unit cell dimension close to those for the parent Tp or Pc liquid crystals was observed. The Pc columns packed either randomly or in a hexagonal superlattice in the Tp matrix. When the spacer length was short (C6), the Tp arms and the Pc core were tightly coupled together, and thus the whole supermolecules stacked together to form a super-LC column. A column-in-column rectangular mesophase with unit cell dimensions close to the size of the entire supermolecule was observed.