P-type doped polypyrrole

The electronic absorption spectra of p-type-doped polypyrrole have been interpreted in terms of polarons and bipolarons for the first time [112]. Electronic absorption spectra of doped polypyrrole in the range from visible to NIR show three bands due to intragap transitions at low dopant contents and two bands at high dopant contents [113]. The three bands are attributed to polarons and the two bands to bipolarons [112], because a polaron is expected to have three intragap transitions and a bipolaron is expected to have two intragap transitions (see Section 4.4.2). A quantitative ESR study [114] has confirmed the interpretation of the electronic absorption experiments. This rule of thumb for band assignment has so far also been applied to other conducting polymers. 

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