Polarized doping-induced infrared absorption in highly oriented conjugated polymers

We present polarized, doping-induced absorption spectra obtained from conjugated polymers oriented by gel-processing in ultrahigh molecular weight polyethylene. Upon doping with iodine vapor, both poly(2-methoxy, 5-(2′-ethyl)-hexyloxy) paraphenylene vinylene), MEH-PPV, and poly (3-octyl thiophene), P3OT, show absorption features in the mid-infrared (the infrared-active vibrational (IRAV) modes and the low energy electronic absorption) that are strongly polarized parallel to the chain axis. All observed features have predominantly parallel polarization. We suggest that carrier-induced and electrode-induced losses in electrically pumped waveguide structures could be greatly reduced by using highly oriented films, with molecular axes orthogonal to the electric field polarization of the waveguide mode.