Photoreactive Langmuir-Blodgett-Kuhn Multilayer Assemblies from Functionalized Liquid-crystalline Side Chain Polymers, I. Homopolymers Containing Azobenzene Chromophores

Stable monomolecular layers of a liquid-crystalline homopolymer bearing azobenzene chromophores in the mesogenic side groups could be prepared at the water-air interface by slow compression at room temperature. From the area per monomer unit of Ap0.25 nm2 a structural model with tightly packed azobenzene groups oriented nearly parallel to the surface normal was deduced. After transfer to a solid support in a Y-type mode the obtained Langmuir-Blodgett-Kuhn ( LBK) multilayer assemblies of varying thicknesses {from a double layer to a thick film of d = 238 nm, capable of guiding optical modes) were prepared and analyzed by X-ray reflection and optical evanescent wave techniques. A monolayer thickness of &= 2.52 nm, as well as the anisotropic index of refraction of these layers, could thus be evaluated. Photo-isomerization by UV-irradiation (at 1 = ( 360f30) nm)was examined by UV-VlS absorption spectroscopy. X-ray reflectivity data of samples illuminated for 30 min showed a complete loss of the layered structure of the LBK samples. As a result strongly light-scattering films were obtained. Surface plasmon microscopy was used to demonstrate the usefulness of this photo-induced order-disorder transition for optical information storage.