Metal-metal interactions in a novel hybrid metallopolymer

A conjugated polymer-redox polymer hybrid based on the complexation of poly[2-(2-pyridyl)bibenzimidazole] with bis(2,2'-bipyridyl)Ru2+ has been prepared to take advantage of electronic communication between metal centers through the conjugated backbone. The existence of such communication is confirmed by the observation of an intervalence charge-transfer band in the near-IR spectrum of the Ru(III/II) mixed valence state. Electron transport studies by rotating disk voltammetry, dual (sandwich) electrode voltammetry, and impedance spectroscopy have yielded electron diffusion coefficients (D-e) of over 10(-8) cm(2) s(-1) for the Ru(III/II) mixed valence state. D-e in nonconjugated Ru(2,2'-bipyridyl)(3)(3+/2+)-type polymers is typically less than this by at least a factor of 10, indicating that electron transport in the new polymer is enhanced by communication of metal centers through the backbone. The redox potential of the Ru sites, and D-e, can be manipulated by changing the electron density on the polymer backbone via pH control of the degree of protonation of the imidazole moieties.