Post-Overoxidation Self-Recovery of Polypyrrole Doped with a Metallacarborane Anion

By using the metallacarborane [Co(C2B9H11)2]-, [1]-, as a doping anion, PPy materials can be made 300−500 mV more resistant to overoxidation. These materials are written as PPy/[A] to indicate a noncovalency between the anion and the PPy and have a clear overoxidation resistance limit, ORL, so that once this is surpassed the material becomes permanently nonelectroactive or dead. On the contrary if [Co(C2B9H11)2]- is chemically bonded to pyrrole through a spacer and then is copolymerized with pyrrole the resulting material, PPy−[1sp], has an electroactive behavior similar to PPy/[A] so that once an apparent ORL is reached the PPy−[1sp] becomes electroinactive but, very importantly, in few hours recovers the electroactivity. The situation is so attractive that even in the case that the overoxidation threshold was surpassed the system would react to restore itself. In this paper we demonstrate that [1]- not only enhances the overoxidation resistance but that, if grafted to the PPy strand, the applied voltage that can sustain the new material can go far beyond the overoxidation limit of the compositionally similar material with, however, no anion grafting. These properties are due to grafting of the metallacarborane to the PPy and have not been observed before. This behavior is not a consequence of the anion grafting to the PPy but depends on the nature of the anion.