Counter-ion induced solubility of polypyridines

Protonating the pyridine rings of poly(2,5-pyridine) and the chloro-substituted prepolymer; of poly(2,5-pyridine vinylene) with dodecylbenzenesulfonic acid produces polymers which can be dissolved in chloroform. This contrasts to the unprotonated polymers, which can only be dissolved in strong acids such as formic acid. This allows mixing df these polymers with other chloroform soluble conjugated polymers for use in photodiodes/solar cells. Both the prepolymer of poly(2,5-pyridine vinylene) and its protonated form can be converted to the conjugated form by heat treatment. The absorption maximum is red-shifted about 60 nm, because of the changed electronic structure.