Excited state electronic properties of the [(phen)(OC)(3)Re-I(NC)Ru-II(bpy)(2)(CN)]PF6 and [(phen)(OC)(3)Re-I(CN)Ru-II(bpy)(2)(CN)]PF6 linkage isomers

The results of temperature dependent emission lifetimes, emission spectral fitting and excited state transient absorption spectroscopy of the two hete ro-dinuclear [(phen)(OC)(3)Re-I(CN)Ru-II(bpy)(2)(CN)](+) and [(phen)(OC)(3) Re-I(NC)Ru-II(bpy)(2)(CN)](+) linkage isomers (abbreviated Re-CN-Ru and Re- NC-Ru) have been examined. In both dinuclear species efficient intramolecul ar Re*--> Ru energy transfer occurs, leading to population of emitting d(pi )(Ru)-pi*(bpy), (MLCT)-M-3 states. The temperature dependent emission data suggest that the barrier for the MLCT-dd surface crossing is smaller in mag nitude when the "[(phen)(OC)(3)Re(NC)]" moiety is bound to the Ru(bpy)(2)(C N) emitting unit. This is interpreted as the result of its enhanced ability to backbond from Ru-II which increases the energy of the MLCT relative to the dd states.