Separation of Neutral-to-Polaron and Polaron-to-Bipolaron Redox Events in AlkoxySubstituted Di-2-Thienylphenylene Polymers

摘要

In situ electron paramagnetic resonance (EPR)/electrochemistry methods have beenused to elucidate the potential dependence of the presence of polaron and bipolaron charge carriers in poly(di-2-thienyl-2,5 diheptoxyphenylene). The identification of charge carriers in conjugated conducting polymers has recently received a great amount of attention. It is generally accepted that the electrochemical oxidation of polyheterocycles leads to the formation of delocalized radical cations (polarons) and ultimately to delocalized dications (bipolarons). Studies involving the electrochemical oxidation and reduction of conducting polyheterocycle films have suggested that the generation of polarons, and the subsequent formation of bipolarons, occurs at essentially the same potential. The potentials of these redox events appear to be too close to allow them to be distinguished by voltammetry. In situ EPR measurements carried out in an electrochemical cell have verified the presence of spin containing species (polarons) at intermediate doping levels in polypyrrole and polythiophene. The relative stability of the polaron intermediate has still not been fully elucidated; particularly in the case of polythiophene.