Abstract
As observed earlier for related excited states in 4:1 (v/v) ethanol/methanol from 90 to 170 K, emission energies for the metal-to-ligand charge transfer (MLCT) excited states of (Os(bpy)/sub 3/)/sup 2 +/ and (Os(bpy)/sub 2/(CO)(py))/sup 2 +/ shift to lower energies while the lifetimes of the excited states decrease with increasing temperature. From temperature-dependent emission spectral fitting and lifetime data it is concluded that the origin of the effect is in the response of solvent dipole orientations to the changes in electronic configuration between ground and excited states and how it affects the energy gap between the states. For (Os(bpy)/sub 2/(CO)(py))/sup 2 +/, the nonradiative rate constant (k/sub nr/) varies with the energy gap, ln (k/sub nr/) proportional to -E, as predicted by the energy gap law, while for (Os(bpy)/sub 3/)/sup 2 +/ additional complications appear to exist because of contributions to excited-state decay from more than one low-lying MLCT state.
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