IV Photoinduced Molecular Orientation in Azopolymers.

Azobenzene containing polymeric systems have been a subject of intensive research in the last few years in the areas of photofunctional applications such as photon-mode optical memories, transducing optical information, photoswitching of electron conductivity, diffraction optics, slab waveguides and are also of interest in non-linear optics due to their high hyperpolarizability. The main interest of such doped or functionalized systems is due to their dichroic and birefringent properties when they are illuminated by a polarized light. Such an effect is a consequence of the reversible "trans-cis" photoisomerization with respect to the N=N double bond which causes a redistribution in the orientation of photochromic entities in a perpendicular direction with respect to the incident electric field. These processes are occuring below the glass transition temperature of the polymer, are stable (in functionalized polymer), and many cycles of 'writing' (upon linearly polarized light) and 'erazing' (upon circularly polarized light) can be induced.

Photoisomerization and angular reorientation of azobenzene molecules.
Presently, the photoisomerization and angular reorientation dynamics of azobenzene- based polymer systems are not fully understood. In this context, our goal is to develop spectroscopic techniques, such as polarized UV-Vis and polarization modulation FTIR spectroscopy, to probe in-situ molecular dynamics of the azobenzene molecules embedded in a polymer matrix. Our most recent works focuses on liquid crystalline polymers with an emphasis on the measurement of the linear and circular anisotropy. Linear dichroism/birefringence and circular dichroism/birefringence are measured with a high precision (better than ?A<10-5) in the visible and infrared domains.