ESR study of electrochemical doping in the conducting polymer polypyrrole

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Abstract
Steady-state and transient measurements of spin concentration have been carried out as a function of electrochemical charge injection in polypyrrole. A maximum of one spin per ∼10 pyrrole units has been observed for about 50% of the maximum charge. The data are interpreted in terms of quasiequilibrium polaron and bipolaron populations resulting from a two-step redox process. Surprisingly, it appears that at low doping levels, bipolaron formation is not favorable compared to formation of two polarons.