N-Methyl-N'-(6-4H-cyclopenta[2,1-b:3,4-b']dithiophene-4-ylhexyl)-4,4'-bipyridinium dihexafluorophosphate (CPDT-V2+-Me) was synthesized. The monomer was electropolymerized on a glassy carbon or an ITO electrode in a potentiodynamic mode to form the corresponding polymer P(CPDT-V2+-Me) on the electrodes. During the electropolymerization, two redox peaks of the viologen (V) moiety increased up to several cycles and then decreased while the redox peak of P(CPDT) moiety still increased. Especially, a new oxidative peak a in the range of ca. -0.4 and 0 V versus Ag/Ag+ appeared and increased up to several cycles. Peak a almost disappeared after the redox peaks of the viologen moiety almost disappeared. As a result of cyclic voltammetric study, it was shown that peak a originated from the oxidation of reduced viologen moiety via P(CPDT)-mediated electron transfer mechanism. We also found that the electroactivity of viologen moiety in P(CPDT-V2+-Me) decreased significantly when the potential was scanned to the second viologen redox (V-0/V.+). In practical applications, the polymer can be used in the potential range from the first viologen redox to P(CPDT) redox. The polymer turned into highly transparent P(CPDTalpha+-V2+-Me), blue P(CPDT-V2+-Me), dark violet P(CPDT-V.+-Me), and violet P(CPDT-V-0-Me) approximately at 0.8, -0.4, -0.8, and -1.7 V versus Ag/Ag+, respectively. (C) 2003 Elsevier Ltd. All rights reserved.