Polaron and bipolaron transitions in doped poly(p-phenylene vinylene) films

This paper describes the oxidation process (chemical doping) of the poly(p-phenine vinylene) (PPV) by using iodine vapor, sulfuric acid and ferric chloride to determine the vibrational and electronics modifications caused by the polymer backbone oxidation. The vibrational spectroscopy indicates that a quinoid structure is formed upon oxidation, coexisting with the original benzoid structure, independent of the doping agent. Only the intensity of the bands changes with the nature of the dopant used. From the electronic spectra, three subgap transitions were identified, indicating the formation of polaronic charge carriers. However, by following different doping levels with I2 doping, bipolaron formation is identified as well showing that polaron and bipolaron coexist as charge carriers in the oxidized polymer. The subgap transitions were peaked at 688, 1724 and 2292 nm for I2; 600, 1360 and 1999 nm for FeCl3; and 603, 1337, 2082 nm for H2SO4 doping.