Long-range photoinduced electron transfer dynamics in rigid media.In semi-rigid PEG-DMA550 films with added reductive quenchers, electron transfer quenching of the metal-to-ligand charge transfer excited state(s) of [Ru(bpy)3](2+) (bpy = 2,2'-bipyridine) occurs by both rapid, fixed-site, and slow, diffusional, quenching processes.  Stern-Volmer analysis of diffusional quenching reveals diffusion-controlled quenching both in the fluid and film with the latter greatly inhibited by the high viscosity of the medium.  The data for fixed-site quenching are consistent with electron tunneling with the expected exponential distance dependence.  Based on this analysis long-range electron transfer occurs with a distance attenuation factor β of ∼0.47 Å(-1) with a notable decrease, β = 0.16 Å(-1), when the quencher is incorporated into the PEG backbone.  Fixed-site electron transfer quenching varies with driving force.  Back electron transfer is complex, as expected for a distribution of fixed sites, and varies with power law kinetics.
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