Anodic coupling of some (4H-cyclopentadithien-4-yl)alkylammonium perchlorates in acetonitrile + 0.1 M Bu4NClO4 produces polycationic polythiophene films with high conjugation length (lambda (max) = 590-600 nm; E degrees = -0.3 V vs Ag/Ag+), conductivity (0.5-2 S cm(-1)), and solubility in organic solvents such as ethanol and acetonitrile. The 4-hexyl-substituted polymer is reversibly reduced (n-doped) at E degrees = -2.08 V. Electrochemical quartz crystal microbalance measurements of the ion flux during n-doping in acetonitrile have shown that anion ejection is dominant over cation injection, attaining 90-95% of the total ion flux. The kinetics of the n-doping process has been investigated by cyclic voltammetry in comparison with that of the analogous 4,4 ' -dihexyl-substituted polymer. In the latter cation injection is slower and shows a strong dependence on the cation size.