OPTICAL ANISOTROPY IN THIN-FILMS OF A BLUE ELECTROLUMINESCENT CONJUGATED POLYMER

We determined the anisotropic optical constants of thin films of a con jugated polymer, the methyl-substituted ladder-type poly(paraphenylene ) (m-LPPP), over a large spectral range between 1.55 and 3.5 eV, In th e subgap region the anisotropic refractive indices were obtained via w aveguiding experiments at 1.55 eV and 1.95 eV. Propagation loss measur ements revealed that the absorption coefficient parallel to the polyme r film surface is very small (< 12.6 cm(-1)) in this energy region, du e to the high purity of the polymer. In the strongly absorbing energy region of the pi-pi electronic transition (2.6-3.5 eV) we performed sp ectroscopic ellipsometric measurements, in order to determine the anis otropic optical constants parallel (N-o) and perpendicular (N-c) to th e polymer surface, The optical anisotropy in the m-LPPP films can be a ttributed to a preferential orientation of the polymer chains in the p lane of the substrate. (C) 1997 Elsevier Science S.A.