Reflectance anisotropy spectroscopy of oriented films of semiconducting polymers

We present reflectance anisotropy spectroscopy (RAS) data for aligned films of luminescent conjugated polymers. Ultrathin films (5–10 nm) spin-cast onto friction-deposited poly-tetrafluoroethylene (PTFE) show birefringence and dichroism indicating alignment of the polymer chains with the PTFE axis. The observed dichroism agrees very well with recently published polarized ultraviolet absorption spectra. In particular, the spectrum of a derivative of poly (para-phenylene) shows the onset of a perpendicular-polarized absorption feature at 5 eV, consistent with recent theoretical predictions. Thick films, prepared by gel-processing in polyethylene (PE), also show characteristic optical anisotropy, and the RAS results are interpreted in terms of the ellipsometric functions, Ψ and Δ.