Self-doped conducting polymers

The sodium salts and the 'proton salts' (acids) of poly-3-(2-ethanesulfonate)thiophene and of poly-3-(4-butanesulfonate)thiophene are the first known examples of water-soluble conducting polymers. In these polymers the counterions are covalently bound to the polymer backbone, leading to the self-doping concept. In a self-doped conjugated polymer, charge injected into the π-electron system is compensated by proton (or Li+, Na+, etc.) ejection, leaving behind the oppositely charged counterion.