A MECHANISTIC STUDY OF THE ELECTROCHEMICAL OXIDATION OF 2,5-BIS(2-THIENYL)PYRROLES

A series of 2,5-bis(2-thienyl)pyrroles has been synthesized in which the alpha-thiophene protons and/or the beta-pyrrole protons have been replaced by Me or Br substituents. A systematic electrochemical investigation of these compounds has yielded rate constants of 36 000 M-1 s-1 for linear coupling of the electrochemically generated cation radicals and 14 000-17 000 M-1 s-1 for branched coupling reactions of the cation radicals. These results constitute the first kinetic evidence for appreciable branched coupling of the electrochemical radical cations of an oligomer precursor of a conducting polymer.