EXAFS studies of iodine-doped poly(octylthiophene)

Iodine doping of poly(octylthiophene) has been studied by EXAFS. At l ow doping levels, the average interatomic I-I distance is close to 2. 9 Å, whic shows that the iodine is present mainly as triiodide ((I3)- ). When the doping level is increased towards saturation (two I atoms per monomer), the distance decreases gradually to 2.73 Å. This is in terpreted as the presence of higher iodine complexes, involving I2 - like units, such as pentaiodide (I5)-. The measured coordination numb ers support this interpretation. The ratio between tri- and pentaiodi de decreases monotonically with the total I content.