EXAFS studies of iodine-doped poly(octylthiophene)

Iodine doping of poly(octylthiophene) has been studied by EXAFS. At low doping levels, the average interatomic I-I distance is close to 2.9 Å, which shows that the iodine is present mainly as triiodide. When the doping level is increased towards saturation (two I atoms per monomer), the distance decreases gradually to 2.73 Å. This is interpreted as the presence of higher iodine complexes, involving I2-like units, such as pentaiodide. The measured coordination numbers support this interpretation. The ratio between I3− and I5− decreases monotonically with the total I content. In this model, the i3− content saturates at a total iodine content around 0.5 I atoms per monomer.