Excited State Intervalence Transfer in a Rigid Polymeric Film

The ligand-bridged complex cis,cis-[(bpy)2ClRu(pz)RuCl(bpy)2]2+ as the PF6- salt, (1)(PF6)2, is stabilized toward photochemical ligand loss in poly(methyl methacrylate) (PMMA). Stabilization allows measurement of metal-to-ligand charge transfer (MLCT) photophysical properties--emission and transient absorption. This includes appearance of an intervalence transfer absorption band in the near IR spectrum of the photochemically prepared, mixed valence form, [(bpy)2ClRuIII(pz(-*))RuIICl(bpy)2](PF6)2* (1*(PF6)2). Comparison of its IT band properties with those of ground state cis,cis-(bpy)2ClRuIII(pz)RuIICl(bpy)2]3+ in CD3CN allows a comparison to be made between pz and pz(-*) as bridging ligands. A model based on differences between rigid and fluid media provides an explanation for decreased IT band energies and widths in PMMA and provides important insight into electron transfer in rigid media.