title: Turning the [Ru(bpy)2dppz]2+ light-switch on and off with temperature.
abstract: We report temperature-dependent excited-state lifetime measurements on [Ru(bpy)(2)dppz](2+) in both protic and aprotic solvents. These experiments yield a unifying picture of the excited-state photophysics that accounts for observations in both types of solvent. Our measurements support the notion of bpy-like and phz-like states associated with the dppz ligand and show that the ligand orbital associated with the bright state is similar in size to the corresponding orbital in the (3)MLCT state of [Ru(bpy)(3)](2+). In contrast to the current thinking, the experiments presented here indicate that the light-switch effect is not driven by a state reversal. Rather, they suggest that the dark state is always lowest in energy, even in aprotic solvents, and that the light-switch behavior is the result of a competition between energetic factors that favor the dark state and entropic factors that favor the bright (bpy) state.
authors.affiliation: Venable and Kenan Laboratories, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Brennaman
authors.forename: James H
authors.initials: JH
authors.lastname: Alstrum-Acevedo
authors.forename: Cavan N
authors.initials: CN
authors.lastname: Fleming
authors.forename: Paul
authors.initials: P
authors.lastname: Jang
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer
authors.forename: John M
authors.initials: JM
authors.lastname: Papanikolas
mesh_terms: D015342:DNA Probes / Q000737:chemistry; D007700:Kinetics; D008163:Luminescent Measurements; D009942:Organometallic Compounds / Q000737:chemistry*; D010619:Phenazines / Q000737:chemistry*; D010777:Photochemistry; D012428:Ruthenium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D015342:DNA Probes; D009942:Organometallic Compounds; D010619:Phenazines; D012428:Ruthenium; C077849:bis(2,2'-bipyridyl)(dipyrido(3,2-alpha-2',3'-c)phenazine)ruthenium (II)