ORIENTATION OF A PHOTO-SENSITIVE POLYMERIC MONOLAYER STUDIED BY 2ND-HARMONIC GENERATION

We determine the orientational distribution functions of ate-side-chai n polymeric monolayers before and after the photo-irradiation by optic al surface second-harmonic generation (SHG). The polymeric monolayer, composed of azo-dye-labeled polyamic acid (long alkyl) amine salt, is prepared by the Langmuir-Blodgett technique. Oblique incident surface SHG measurement from the monolayer provides the nonlinear-optical tens or components related to the orientational distribution functions of t he azo-side-chain. The analysis of experimental results shows that the point symmetry of the azo-pendent unit in the monolayer changes from C-infinity upsilon to C-1 upsilon by the photo-isomerization process w ith the azobenzene conformation retained as trans-isomer.