Impact of core chirality on mesophase properties of perylene bisimides

The three-dimensional organisation of a racemic core-twisted perylene bisimide (PBI) 1 and its pure atropo-enantiomers ((P)-1 and (M)-1) are compared in the condensed state to elucidate the impact of core chirality in such materials. Our studies revealed distinctive differences in the condensed state properties of the racemic and enantiopure PBIs. While the racemic material forms a soft crystalline phase, the pure enantiomers (P)-1 and (M)-1 exhibit a smectic liquid crystalline mesophase of much lower viscosity as evidenced by differential scanning calorimetry (DSC), polarization optical microscopy (POM), X-ray diffraction of extruded samples and atomic force microscopy (AFM) investigations. Two different packing models for the condensed state of the racemate and its pure enantiomers have been proposed based on the observed mesophase properties and force field calculations.