Bipolarons in Doped Conjugated Polymers: A Critical Comparison Between Theoretical Results and Experimental Data

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Abstract
Adopting a language common to both physicists and chemists, we discuss the origin of formation of radical-ions (polarons) and diions (bipolarons) upon doping of conjugated polymers with a nondegenerate ground state. We present a review of some of the calculations we have devoted to the influence of doping on the geometric and electronic properties of the polymer chains. We critically compare the theoretical results with experimental data, such as the evolution of the optical and magnetic properties upon doping. The bipolaron model is shown to provide a coherent and unified picture of the properties of doped conducting polymers. We point out the relationship between bandgap and bondlength alternation in polymers based on aromatic rings. We demonstrate it is very different from that found in polyacetylene-like compounds and comment on the possibility of obtaining small bandgap conjugated polymers.