T. Tanaka et al., Highly anisotropic molecular thin films prepared by oriented growth on poly(tetrafluoroethylene) surfaces, LANGMUIR, 17(7), 2001, pp. 2192-2198
Highly anisotropic molecular thin films have been successfully prepared by
depositing bisazo dyes under vacuum through evaporation on an oriented poly
(tetrafluoroethylene) (PTFE) surface aligned by rubbing or a friction-trans
fer technique. Polarized absorption spectra (UV-visible and IR), electron d
iffraction, optical microscopy, and Raman scattering were employed to inves
tigate the molecular orientation in the films. The results indicate that th
e dye molecules are oriented with their long axes parallel to the PTFE chai
ns and that their phenyl rings are fairly parallel to the substrate surface
. Slight modifications of the dye molecules lead to significant changes in
the degree of the orientation. In particular, the films from a bisazo dye c
ontaining a pyrrolidinyl group exhibit a remarkable orientation, showing di
chroic ratios up to 130 on the polarized UV-visible spectra.