A new strategy for functionalizing oligothiophenes is the transformation of the thienyl sulphurs into the corresponding S,S dioxides, with the effect of lowering the LUMO energy without significantly affecting the HOMO one. From a quinquethiophene S,S dioxide derivative, a polymer (pQTDO) which can be reversibly n-doped at not very negative potentials still maintaining the property of being p-doped at moderate potential Values was electrosynthesized. There is, however, a great difference in the ability to store charge of the polymer＇s p- and n-doped forms: a great amount of injected negative charge irreversibly modifies the structure of pQTDO. (C) 2000 Elsevier Science Ltd. All rights reserved.