Turning the [Ru(bpy)2dppz]2+ Light-Switch On and Off with Temperature

• Published in: Journal of the American Chemical Society 2002-12, Vol.124 (50), p.15094-15098
• Main Authors: Brennaman, Matthew K, Alstrum-Acevedo, James H, Fleming, Cavan N, Jang, Paul, Meyer, Thomas J, Papanikolas, John M
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; DNA Probes - chemistry; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Kinetics; Luminescent Measurements; Molecular properties and interactions with photons; Organometallic Compounds - chemistry; Phenazines - chemistry; Photochemistry; Physics; Radiationless transitions, quenching; Ruthenium - chemistry; Thermodynamics
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0279139

We report temperature-dependent excited-state lifetime measurements on [Ru(bpy)2dppz]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 3MLCT 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.