The preparation and electrochemical characterization using cyclic voltammetry, in situ quartz crystal microbalance measurements and ac impedance spectroscopy of five new monomers and polymers for electrochemical capacitors (ECC) are described. High polymerization efficiencies (similar to 70%) and charge densities (similar to 190 C g(-1)) were obtained for poly 3-(3,4-difluorophenylthiophene), MPFPT, and poly 3-(4-fluorophenylthiophene), PFPT. Excellent cycling stability (< 1% degradation over 100 cycles) was achieved for MPFPT in both p-and n-doping regimes. This enhanced cyclability is associated with polymers having rigid open structures.