In situ FTIR studies on the redox properties of poly(thiophene-3-methanol) in PF −6 and ClO −4 electrolytes

Abstract

In order to gain more information on the role of charge compensating anions, the COC coupled monomer units and the free CH 2OH substituents in the oxidation process of electrosynthesized poly(thiophene-3-methanol) (PTOH), in situ external reflectance FTIR spectra were recorded during the oxidation and reduction of PTOH ClO 4 and PTOH PF 6 films. The voltammetric results indicate a strong memory effect with regard to the anion used in the synthesis of PTOH. Nevertheless, both PTOH ClO 4 and PTOH PF 6 films show similar features in the infrared. The IR spectra of the oxidized films are characterized by electronic absorption and enhancement of some vibrational modes due to coupling of the movement of the charge carriers with the polymer lattice vibrations. In addition, bipolar carbonyl bands and bands due to intake of anions are observed. The asymmetric stretching band of ClO − 4 ions inside the film was found to shift about 15 cm −1 from its value in solution, indicating an interaction between this anion and the polymer lattice. The spectra registered from successive oxidation and reduction steps of PTOH show bands due to the formation of COC bonds, which confirms our hypothesis of an EC type of oxidation of PTOH. It is shown that the volume changes of PTOH films during charging and discharging can be followed by FTIR spectroscopy.