Ring-Opening Polymerization of Pyridinium Salts

Significance

The authors report the ring-opening polymerization of pyridinium salts 1 with piperazine. The polymers 2 display unique absorption characteristics in methanol, with the λ_max of solution samples blue-shifting more than 50 nm when left standing. The authors propose that this apparent change in conjugation length is caused by the conversion of the piperizinium rings from a boat-to-chair conformation, which is less favorable for orbital overlap. The model compounds they synthesize (4) do not show the same behavior.