Uniaxial alignment of polycyclic aromatic hydrocarbons by solution processing

The self-organization of two polycyclic aromatic hydrocarbons with different aromatic core sizes, dodecylphenyl-substituted hexa-peri-hexabenzocoronene and an extended disk consisting of 96 carbon atoms 6-fold-alkyl-substituted, on the surface from solution has been investigated. Highly ordered surface layers of both materials could be obtained by the zone-casting technique, despite an apparently low self-organization in drop-cast films. The zone-cast films revealed high macroscopic uniaxial orientation of the columns with a molecular edge-on arrangement on the glass support as confirmed by polarized optical microscopy, UV-vis measurements I in polarized light, high-resolution transmission electron microscopy, and X-ray diffraction. Electron diffraction indicated a high intracolumnar periodicity of the molecules, but a low intercolumnar correlation of the disks due to the increased molecular dynamics in the liquid crystalline phase.