Polygonal cylinder phases of 3-Alkyl-2,5-diphenylthiophene-based bolaamphiphiles: Changing symmetry by retaining net topology

Novel bolaamphilic triblock molecules consisting of a bent 2,5-diphenylthiophene unit, two terminal glycerol units, and a lateral n-alkyl chain have been synthesized via Ni- and Pd-catalyzed coupling reactions as key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light optical microscopy, DSC, and X-ray scattering and the influence of the length of the lateral alkyl chains on the mesomorphic properties was studied. With elongation of the lateral alkyl chains, three different columnar phases (Col_squ/p4mm, Col_squ/p4gm and Col_hex/p6mm), representing polygonal cylinder structures were found, where the cells have a square, pentagonal, and hexagonal cross-section, respectively. In the observed phase sequence, the change of the net topology is the same as seen for related linear biphenyl derived bolaamphiphiles, but the symmetry is increased, i.e, rectangular phases are replaced by square lattices.