Journal
CHEMISTRY-AN ASIAN JOURNAL
Volume 5, Issue 9, Pages 2036-2046Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/asia.201000033
Keywords
density functional calculations; N ligands; photophysics; raman spectroscopy; ruthenium
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Funding
- MacDiarmid Institute for Advanced Materials and Nanotechnology
- Massey University
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A recently reported new class of ruthenium complexes containing 2,2'-bipyridine and a dipyrrin ligand in the coordination sphere exhibit both strong metal-to-ligand charge-transfer (MLCT) and pi-pi* transitions. Quantitative analysis of the resonance Raman scattering intensities and absorption spectra reveals only weak electronic interactions between these states despite direct coordination of the bipyridyl and dipyrrin ligands to the central ruthenium atom. On the basis of DFT calculations and time-dependent DFT (TD-DFT), we propose that the electronic excited states closely resemble pure MLCT and pi-pi* states. Resonance Raman intensity analysis demonstrates that a large amplitude transannular torsional motion provides a mechanism for relaxation on the pi-pi* excited-state surface. We assert that this result is generally applicable to a range of dipyrrin complexes such as boron-dipyrrin and metallodipyrrin systems. Despite the large torsional distortion between the phenyl ring and the dipyrromethene plane, pi-pi* excitation extends out onto the phenyl ring which may have important consequences in solar-energy-conversion applications of ruthenium-dipyrrin complexes.
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