Synthesis of polysiloxanes with pendant viologen groups and their characteristic behavior of aggregation and deposition observed on electron transfer

In order to prepare polysiloxanes with the ability of electron transport, pendant viologen groups were introduced. Chloromethylated poly(methyl-β-phenethylsiloxane) (2) was reacted with monoalkylbipyridinium chlorides (3a, 3b) to give polysiloxanes (4a, 4b) containing pendant viologen groups. These polymers show reversible redox behavior. They are deposited on ITO electrodes when the pendant viologen dication groups are electrochemically reduced to cation radicals. The polymer deposited shows an absorption maximum (λmax) at 500 nm, which is due to a highly aggregated structure of cation radicals. On the contrary, when the electrode was coated by the polymer before the measurement (pre-cast membrane), the cation radicals formed electrochemically show λmax at 530 nm, indicating that the degree of aggregation is lower than that in the membrane formed reductively from solution.