Highly Oriented Films Of Polydiacetylene For Non Linear Optics: Epitaxial Growth Of Dch Monomer And Optical Properties Of Polymerized Films

Thin films of a diacetylene derivative with carbazol substituents have been prepared under vacuum by epitaxial growth on an organic single crystal. We have been able to obtain these films on large crystals with an area of about 10 cm2. The thermal topochemical polymerization in the solid state has been performed on the film laying on the substrate. The resulting polycrystalline film (pDCH) is uniaxially oriented along a privileged direction of the single crystal substrate as shown by electron microscopy. The sizes of the crystals are in the range of 0.1 to 0.3 μm and some particularly long and well oriented needle crystals can be seen on the surface. Optical studies such as UV-Vis spectroscopy or third harmonic generation (THG) have been performed on these mono-oriented films. The single orientation of the polymer chains and crystals on the organic substrate is perfectly confirmed by the angular dependence of the THG intensity which follows the theoretical law.