Structure characterization of sulfuric acid-doped poly(3-octylthiophene)

The structures of sulfuric acid-doped and water-undoped poly(3-octylthiophene) (P3OT) were investigated by gel permeation chromatography (GPC), elemental analysis (EA), conductivity measurement, ultraviolet-visible-near-Infrared spectroscopy (UV-Vis-near-IR), Electron spin resonance (ESR), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). For H2SO4-doped P3OT, the counter ion is HSO4- and the positive charge formed on the main chain distributes only on the conjugated C-C bond and does not distribute on the S atoms. The conductivity is found to increase by 5 orders as the doping level is 0.22. After the undoping with water, C-OH groups are formed on the main chains, which results in a decrease in conjugating length and in a less order chain arrangement. The undoped P3OT film can be redoped by 98% H2SO4; however, the doping level is less than its original value at the same doping condition.