Polyazulene, A Member of a New Class of Polymers

Abstract

Electrochemical oxidation of azulene in acetonitrile containing an appropriate electrolyte yields thick, electrically conducting polymeric films. Free-standing films of polyazulene peeled off a platinum electrode have electrical conductivities [sgrave]=10⁻² to 1/Ω·cm, depending on the counter-anion, with perchlorate or tetrafluoroborate giving the highest values. Similar polymers are obtained from benzenoid or heterocyclic aromatic monomers, for example, pyrene, triphenylene or carbazole. These polymers resemble the better known polypyrrole.

Spectroscopic evidence shows that the polymer consist of aromatic units, and elemental analysis reveals incorporation of counter-anions from the electrolyte; for polyazulene, one per 4 monomeric units. The consequences of alkyl substituents upon the tendency of the monomer to polymerize reveal that the hypothetical structure of polyazulene is best represented by 1,3-linked azulene units. The reaction mechanism involves dimerization of radical cations and deprotonation via a base. The so obtained oligomers oxidize more readily than the corresponding monomers.