Electronic, chemical and structural change induced by organic solvents in tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-OTs)

The effects of organic solvent on the electronic, structural and chemical properties of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-OTs) are investigated. The use of different organic solvents during the oxidative chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with iron(III)-tosylate can greatly vary the electrical conductivity of PEDOT-OTs along with molecular structure and doping concentration. For example, PEDOT-OTs prepared from methanol shows the conductivity of 20.1 S/cm, which is an increase by a factor of 10⁷ compared to PEDOT-OTs prepared from acetone. From the X-ray diffraction (XRD) experiments, it was found that PEDOT-OTs samples prepared from ketone solvents are amorphous state, whereas PEDOT-OTs samples prepared from alcoholic solvents show the better defined crystalline structure in which the charge transport along and between the PEDOT chains are promoted. Chemical analysis employing X-ray photoelectron spectroscopy (XPS) revealed that the doping concentration of PEDOT-OTs with alcoholic solvents is much higher than that of PEDOT-OTs with ketones. It is proposed that the interactions between the organic solvent and iron(III)-tosylate can cause the variation in doping concentration and, therefore, result in the PEDOT-OTs of different conductivities and chain structures.