Steric Influence on the Excited-State Lifetimes of Ruthenium Complexes with Bipyridyl−Alkanylene−Pyridyl Ligands
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- 作者：Maria Abrahamsson ; Maria J. Lundqvist ; Henriette Wolpher ; Olof Johansson ; Lars Eriksson ; Jonas Bergquist ; Torben Rasmussen ; Hans-Christian Becker ; Leif Hammarströ ; m ; Per-Ola Norrby ; Bjö ; rn &#x
- 刊名：Inorganic Chemistry
- 出版年：2008
- 出版时间：May 5, 2008
- 年：2008
- 卷：47
- 期：9
- 页码：3540 - 3548
- 全文大小：1653K
- 年卷期：v.47,no.9(May 5, 2008)
- ISSN：1520-510X
文摘
The structural effect on the metal-to-ligand charge transfer (MLCT) excited-state lifetime has been investigated in bis-tridentate Ru(II)−polypyridyl complexes based on the terpyridine-like ligands [6-(2,2′-bipyridyl)](2-pyridyl)methane (1) and 2-[6-(2,2′-bipyridyl)]-2-(2-pyridyl)propane (2). A homoleptic ([Ru(2)2]2+) and a heteroleptic complex ([Ru(ttpy)(2)]2+) based on the new ligand 2 have been prepared and their photophysical and structural properties studied experimentally and theoretically and compared to the results for the previously reported [Ru(1)2]2+. The excited-state lifetime of the homoleptic RuII complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding homoleptic RuII complex of ligand 1, containing a methylene bridge. A comparison of the ground-state geometries of the two homoleptic complexes shows that steric interactions involving the isopropylene bridges make the coordination to the central RuII ion less octahedral in [Ru(2)2]2+ than in [Ru(1)2]2+. Calculations indicate that the structural differences in these complexes influence their ligand field splittings as well as the relative stabilities of the triplet metal-to-ligand charge transfer (3MLCT) and metal-centered (3MC) excited states. The large difference in measured excited-state lifetimes for the two homoleptic RuII complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from 3MLCT states to short-lived 3MC states.