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Excited-State Electronic Structure in Polypyridyl Complexes Containing Unsymmetrical Ligands
Kristin M. Omberg1, Gregory D. Smith, Darius A. Kavaliunas
1Department of Chemistry, CB#3290, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, and Department of Chemistry, Duke University, P.O. Box 90346, Durham, North Carolina 27708-0346.
Inorganic Chemistry
|October 24, 2001
Summary
Ruthenium complexes with ester- or amide-modified ligands localize excited electrons onto these ligands. Vibrational analysis reveals electron polarization within unsymmetrical ligands and a strong Ru(III) core interaction in certain excited states.
Area of Science:
- Inorganic Chemistry
- Photochemistry
- Spectroscopy
Background:
- Metal-to-ligand charge transfer (MLCT) excited states are crucial in photochemistry and photophysics.
- Understanding electron distribution and localization in MLCT excited states informs material design.
- Ruthenium polypyridyl complexes are widely studied models for MLCT phenomena.
Purpose of the Study:
- To investigate the excited-state structure of ruthenium complexes with derivatized bipyridine ligands.
- To determine the localization and polarization of electrons in MLCT excited states.
- To elucidate the role of ester and amide substituents in influencing excited-state dynamics.
Main Methods:
- Utilized step-scan Fourier transform infrared absorption difference time-resolved (S(2)FTIR ΔA TRS) spectroscopy.
- Employed time-resolved resonance Raman (TR(3)) spectroscopy to probe vibrational modes.
- Analyzed vibrational data, specifically carbonyl (CO) stretching frequency shifts (Δν(CO)).
Main Results:
- Identified ester- or amide-derivatized ligands as the primary electron acceptors in MLCT excited states.
- Confirmed excited electron localization on a single acceptor ligand within the nanosecond timescale.
- Observed significant electron polarization towards derivatized pyridine rings in unsymmetrically substituted ligands.
- Quantified reduced Δν(CO) values in certain complexes, indicating strong polarization between the Ru(III) core and the excited electron.
Conclusions:
- The excited electron in these Ru complexes is primarily localized on the functionalized bipyridine ligand.
- Substituent type (ester vs. amide) and position influence electron distribution and polarization.
- Strong electronic interactions in the excited state affect vibrational frequencies and provide insights into charge distribution.