Electron transport in Ru and Os polybenzimidazole-based metallopolymers

A series of conjugated polymer-redox polymer hybrids based on the complexation of poly-(bibenzimidazoles) with bis-(2,2 ' -bipyridyl)Ru2+ and bis-(2,2 ' -bipyridyl)Os2+ has been prepared to investigate the effects of electronic communication between metal centers through the conjugated backbone. Electron transport rates in the mixed valence M(III/II) states have been measured as electron diffusion coefficients (D-e) by impedance spectroscopy and dual (sandwich) electrode voltammetry. D-e values are generally higher than for nonconjugated Ru (2,2 ' -bipyridyl)(3)(3-/2+)-type polymers, and their dependencies on the metal (Os or Ru), pH and nature of the polymer backbone are consistent with significant contributions from superexchange mechanisms. Hole-type superexchange appears to dominate in the Ru polymers, while a number of observations indicate that electron-type superexchange may dominate for the Os complexes.