Determination of molecular arrangement in extremely uniaxial solid thin films of a linear bisazo dye

Abstract The molecular arrangement of the extremely uniaxial thin film was determined using X-ray analysis, including grazing incidence wide-angle X-ray scattering. The highly oriented film was obtained by depositing a bisazo dye onto an aligned polytetrafluoroethylene (PTFE) layer via vacuum evaporation, as shown previously. The X-ray analysis indicated that the molecules are arranged in parallel or antiparallel orientations within the unit cell. Moreover, their long axes are parallel to each other within the grains which are uniformly oriented throughout the film. These results confirm the driving force of the orientation reported previously using a molecular dynamics model: dye molecules trapped along the atomic grooves between adjacent PTFE chains serve as nuclei for crystal growth. In addition, the long molecular axes remain parallel to the rubbing direction, although some grains are inclined in the short-axis direction. This molecular arrangement in the film could contribute to a high degree of uniaxial orientation.