  The molecule 2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene has
gained a lot of attention, since high charge carrier mobility was observed in
thin film transistors. Its thermotropic liquid crystalline states may play an
important role in the thin film formation, since the smectic A and the smectic
E phase (SmE) are claimed to be pre-stages of the final bulk structure. To
understand the phase diversity, structural characterisation of solution
processed thin films are performed by X-ray diffraction in the complete
temperature range up to the isotropic state at 240{\deg}C. The diffraction
pattern of the SmE phase is analysed in detail. Peak broadening analysis
reveals that the crystallographic order across the smectic layers is larger
than the order along the smectic layers. A combined experimental and
computational approach is used to determine the molecular packing within the
SmE phase. It leads to a number of different packing motifs. A comparison of
the calculated diffraction pattern with the experimental results reveals that
nano-segregation is present within the SmE phase. Energy consideration clearly
favours a herringbone arrangement of the aromatic units. The nano-segregation
within the SmE phase with herringbone packing of the aromatic units is
accompanied with interdigidation of sidechains from neighbouring smectic
layers.
