Spontaneous formation of an ordered structure during dip-coating of methylene blue on fused quartz

Molecular orientation in thin films of methylene blue, prepared by dip-coating, has been studied by UV-visible absorption spectroscopy and X-ray diffraction. In multilayered films the molecules are essentially standing normal to the surface of a fused quartz substrate and form a layered structure with a periodicity that corresponds to the molecular length. Due to this arrangement the film is only faintly colored, since, with normal incidence, the electric field of the incident light is orthogonal to the transition moment of the molecules. This structure can be formed by self-organization in the course of drying, not by epitaxy.