Excited state electronic properties of the [(phen)(OC)3ReI(NC)RuII(bpy)2(CN)]PF6 and [(phen)(OC)3ReI(CN)RuII(bpy)2(CN)]PF6 linkage isomers†

Abstract

The results of temperature dependent emission lifetimes, emission spectral fitting and excited state transient absorption spectroscopy of the two hetero-dinuclear [(phen)(OC)₃Re^I(CN)Ru^II(bpy)₂(CN)]⁺ and [(phen)(OC)₃Re^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 intramolecular Re*→Ru energy transfer occurs, leading to population of emitting d_π(Ru)–π*(bpy), ³MLCT states. The temperature dependent emission data suggest that the barrier for the MLCT–dd surface crossing is smaller in magnitude when the “[(phen)(OC)₃Re(NC)]” moiety is bound to the Ru(bpy)₂(CN) 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.