A linear conjugated core for functional columnar liquid crystals

Abstract

Two series of polycatenar molecules consisting of a π-conjugated rigid core derived from 3-hexen-1,5-diyne coupled to different types of benzoic acid derivatives have been prepared and their potential as multifunctional materials has been investigated. The size ratio between the rigid core and the benzoate-derived groups, which vary in bulk, is crucial to address self-organization, thus indicating the delicate balance of forces involved in liquid crystalline (LC) behaviour. LC nematic, crystalline or LC columnar behaviour is observed depending on the structure of the benzoate moiety. Hexagonal two-dimensional columnar organization is attained for mesogens with benzoate-derived groups bearing six and nine alkoxylic tails. The stacking unit of the columnar organizations is different depending on the total number of tails, twelve or eighteen, with two molecules and half a molecule per columnar stratum, respectively. Macroscopic properties related to molecular structure, such as luminescence, chirality and electroactivity, have also been studied. Luminescent behaviour is observed for all mesogenic materials, which show higher Stokes shifts than in solution. In addition, supramolecular chirality in the mesophase has been observed for a chiral mesogen. Finally, the photoconducting behaviour of two of the columnar materials has been evaluated.