Molecular orientation of 4-hydroxy-4′-biphenylcarbonitrile on the polyimide surfaces with long alkyl chains

It is important to have control over the nucleation, growth and orientation of organic thin films. The present study focuses on the orientation the dipolar linear organic molecule, 4-hydroxy-4′-biphenylcarbonitrile (HBC), on aligned polyamide films. The polymer surfaces were oriented by using rubbing method and photo-alignment method. UV–vis spectroscopic study illustrated that the photo-reaction of cinnamate containing polyamide proceed by photo-dimerization reaction. The photo-aligned polyimide can make perpendicular orientation of nematic liquid crystals. The IR absorption intensity ratios of alkyl group versus nitrile group measured with transmission mode and reflection mode are about 2–3 and 1.3, respectively. The low intensity ratio for reflection measurement was due to the CN vibrational mode can be better matched with inclined light and accordingly the absorbance increases. Since the molecules are perpendicular to the surface, the light from inclined angle to the substrate activates the vibration of CN group more effectively. These results clearly demonstrate that the orientation influences the nucleation and oriented growth of aromatic crystals. The crystallinity, mesoscopic and side chain orientation and hydrophobicity of polymer surface are important factors that induce the orientation of guest molecules.