IRREVERSIBLE-PROCESSES IN THE ELECTROCHEMICAL REDUCTION OF POLYTHIOPHENES - CHEMICAL MODIFICATIONS OF THE POLYMER AND CHARGE-TRAPPING PHENOMENA

Irreversible changes occurring in the electrochemical reduction of som e polythiophenes in acetonitrile have been investigated by cyclic volt ammetry (CV), UV-Vis and IR spectroscopy and the electrochemical quart z crystal microbalance (EQCM). Reduction in the presence of alkali met al cations (Li+, Na+, K+ and Cs+) does not result in n-doping but in h ydrogenation of the alkene moieties. The promotion of double-bond satu ration by alkali metal cations following the order Li+, Na+ > K+ > Cs is attributed to their charge-pinning action which decreases as the i on radius is increased. Reversible reduction in tetralkylammonium elec trolyte (n-doping) is accompanied by production of hydroxide ions with in the polymer which are thereby inserted by subsequent oxidation. The resulting quinone-like groups are responsible for the CV pre-peaks us ually observed in conducting polymers after n-doping and previously as signed to trapped charges.