Anisotropy of optical properties of conjugated polymer thin films by spectroscopic ellipsometry

Optical properties of thin films of conjugated poly(arylenephenylene) polymers have been determined using variable angle spectroscopic ellipsometry. Dispersion of the complex refractive index parallel, N∥=(n∥+ik∥), and perpendicular, N⊥=(n⊥+ik⊥), to the film plane are reported for the photon energy range 1.5–5.0 eV. The energy dispersion in the optical properties has been analyzed using a three-phase model and Lorentzian dispersion functions for the polymers. The resonant frequencies of the Lorentzian oscillators describe the fundamental π-π* optical transition polarized parallel to the polymer chain and indicate additional optical transitions polarized perpendicular to the polymer chain that are introduced by interchain interactions. Dependence of the optical anisotropy and fundamental π-π* optical transition on the polymer backbone is discussed.