Electrochemistry and electrochromism of the polythiophene derivative with viologen pendant

N-Methyl-N’-(6-thiophene-3-ylhexyl)-4,4′-bipyridium [Th-V2+-Me] dihexafluorophosphate was synthesized, which can be oxidatively electropolymerized on glassy carbon or ITO electrode, turning the electrode surface into surface-confined polythiophene derivative with electroactive pendant, i.e. viologen moiety. The polymer showed electrochemical activity both of the viologen and polythiophene moieties. Electroactivity of the viologen moiety was almost invariant although electrochemical activity of the polythiophene moiety decreased due to degradation of polythiophene backbone after several doping/dedoping processes. The doped polythiophene moiety was not dedoped completely when the applied potential was above −0.7 V which is the first reduction potential of the viologen moiety. This was explained in terms of the viologen mediated electron transfer reaction. Static and dynamic spectroelectrochemical studies of the polymer were also performed. The red polymer on ITO glass turned transparent or pale blue upon oxidative doping at about 0.8 V and to violet and orange at the potentials of first (−1.0 V) and second viologen reduction (−1.8 V), respectively. On switching the potential between the completely oxidized state and fully reduced state of the viologen moieties, the colors of the mono-valent viologen moieties appeared momentarily before reaching the final colors.