Decay of electrochemically injected polarons in polythiophenes. Bipolaron stabilization by structural factors

In situ ESR measurements have shown that polarons generated in polybithiophene by electrochemical oxidation in acetonitrile decay to bipolarons. The decay follows a first-order kinetic law with half-life times which increase as the oxidation level is increased. This phenomenon is attributed to electrostatic crosslinking which makes the material progressively stiff. Absence of polaron decay has been observed in alkoxy- and alkyl-substituted polythiophenes and attributed to polaron stabilization in the solvent-swollen materials. The structural factors (polymer matrix stiffening or swelling) are shown to be critical parameters in the long-debated stability of polarons in non-degenerate polyconjugated conducting polymers.