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Highly solvent dependent luminescence from [Ru(bpy)(n)(dppp2)(3-n)](2+) (n = 0-2)
1Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.
Inorganic Chemistry
|April 30, 2010
Summary
Ruthenium(II) complexes with the dppp2 ligand show significant solvent-dependent luminescence. This solvent effect is due to the varying stability of metal-to-ligand charge transfer states, impacting emission properties.
Area of Science:
- Inorganic Chemistry
- Photochemistry
- Materials Science
Background:
- Ruthenium(II) complexes are widely studied for their photophysical properties.
- Ligand design significantly influences the luminescence and excited-state behavior of metal complexes.
- Understanding solvent effects is crucial for tuning photophysical properties in solution.
Purpose of the Study:
- To investigate the photophysical properties of ruthenium(II) complexes with the pyrido[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline (dppp2) ligand.
- To explore the impact of solvent polarity on the luminescence characteristics (maximum, lifetime, quantum yield) of these dppp2-containing complexes.
- To elucidate the electronic structure and excited-state dynamics responsible for the observed solvent dependence.
Main Methods:
- Synthesis and characterization of [Ru(bpy)(n)(dppp2)(3-n)](2+) complexes (n=0-3).
- Spectroscopic investigations including steady-state and time-resolved luminescence spectroscopy.
- Transient absorption spectroscopy, electrochemistry, and electronic structure calculations.
Main Results:
- The dppp2 complexes exhibit a pronounced solvent dependence in their luminescence maximum, lifetime, and quantum yield.
- A significant blue shift in emission and a large enhancement in quantum yield were observed with decreasing solvent polarity.
- Electronic structure calculations and transient absorption spectroscopy revealed that the solvent effect arises from the differential stabilization of two low-lying metal-to-ligand charge transfer (MLCT) excited states.
Conclusions:
- The photophysical properties of ruthenium(II)-dppp2 complexes are highly sensitive to the surrounding solvent environment.
- The observed solvent effects are attributed to the relative stabilities of MLCT excited states, with the lowest energy state being more susceptible to solvent polarity.
- The lowest energy excited state in these complexes is a triplet MLCT state localized distally on the dppp2 ligand, distinct from related dppz complexes.
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