Thermally induced transitions of polarons to bipolarons in poly(3-dodecylthiophene)

The influence of thermal activation on polaron interactions of poly(3-dodecylthiophene) (PDDT) was studied. It was found that when an undoped PDDT sample was heated above 450 K and subsequently cooled to under the glass transition temperature, there were strong spin-spin interactions. When the polaron concentration was increased by FeCl3 doping, all polarons including the immobile ones started to interact mutually. Changes in its internal microstructure, caused by thermal activation of the sample, followed by its freezing can generate an amplification of polaron interactions, giving rise to diamagnetic inter- and intra-chain bipolarons. As a result of strong spin-spin interactions the doped polymeric sample of PDDT displays diamagnetism even at room temperature. The diamagnetic properties depend on the consecutive structural relaxation of PDDT, caused either by immediate temperature changes, or by long-term standing at room temperature.