Alignment of a perylene-based ionic self-assembly complex in thermotropic and lyotropic liquid-crystalline phases

The thermotropic and lyotropic liquid-crystalline (LC) phases of the ionic self-assembled complex N,N',-bis(2-(trimethylammonium) ethylene)-perylene-3,4,9,10-tetracarboxyldiimide-bis(2-ethylhexyl)sulfosuccinate have been studied using polarizing microscopy, differential scanning calorimetry (DSC), and X-ray scattering techniques. A two-dimensional (2D) columnar thermotropic LC phase with pi-pi stacking of the perylene tectonic units and a lyotropic LC phase in dimethyl sulfoxide (DMSO) have been found. Different techniques have been applied to align both systems and included: surface interactions, electric and magnetic fields, shear force, and controlled domain formation at the LC-isotropic phase-transition front (PTF). Characterization of the alignment in films has been performed using polarized UV-vis spectroscopy and transmission null-ellipsometry. The best results have been obtained for alignment of the material in a lyotropic phase by controlled domain formation at the PTF of the LC-isotropic phase transition. In this case, a dichroic ratio of 18 is achieved with packing of columns of perylenediimide tectons perpendicular to the PTF.