Redox behavior of pyridinium salts and their polymers having radical stabilizing groups

The redox behavior of pyridinium salts having various substituents capable of stabilizing pyridinyl radicals at the 4-position was investigated by cyclic voltammetry in water with a platinum electrode, and their redox potentials were more positive in the order of 4-substituents of acetyl > cyano > carbomethoxy > carbamide groups. Sodium dithionite was found to be suitable for a chemical reducing agent of the pyridinium salts. Two types of homopolymers with pendant 4-carbamido-pyridinium groups were prepared and their redox potentials were more positive than the corresponding model compounds. The positive shift might be caused by charge repulsion between the neighboring pyridinium cations on the polymer main chain in the oxidized state.