Influence of electronic delocalization in metal-to-ligand charge transfer excited states
- Univ. of North Carolina, Chapel Hill, NC (United States)
In the metal-to-ligand-charge transfer (MLCT) excited states of the ligand-bridged complexes [(dmb){sub 2}Ru({mu}-bbpe)-Ru(dmb){sub 2}](PF{sub 6}){sub 4} and [(bpy){sub 2}Os({mu}-bbpe)Os(bpy){sub 2}](PF{sub 6}){sub 4} (bpy is 2,2{prime}-bipyridine, dmb is 4,4{prime}-dimethyl-2,2{prime}-bipyridine, bbpe is trans-1,2-bis-(4-(4{prime}-methyl)-2,2{prime}bipyridyl)ethene) bbpe acts as the acceptor ligand. This conclusion is based on transient UV-visible and resonance Raman measurements, which also reveal that the excited electron in the Ru complex is localized over the bbpe ligand. Compared to related complexes having comparable energy gaps, the lifetimes of [(dmb){sub 2}Ru({mu}-bbpe)Ru(dmb){sub 2}]{sup 4+*} ({tau} = 1.31 {mu}s in CH{sub 3}CN at 298 K) and [(dmb){sub 2}Ru(bbpe)]{sup 2+*} ({tau} = 1.15 {mu}s in CH{sub 3}CN at 298 K) are unusually long. The extended lifetimes are a delocalization effect caused by decreased bond displacement changes in the excited state. This decreases vibrational overlap between states, and the rate constant for nonradiative decay. Delocalization disperses the excited electron over the molecular framework of the acceptor ligand, decreasing changes in local bond displacements compared to bpy. These results have important implications for the design of complexes which are broad visible light absorbers and yet retain accessible excited state lifetimes.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG05-86ER13633
- OSTI ID:
- 75655
- Journal Information:
- Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 2 Vol. 34; ISSN 0020-1669; ISSN INOCAJ
- Country of Publication:
- United States
- Language:
- English
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