Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands

Maria Abrahamsson, Maria J. Lundqvist, Henriette Wolpher, Olof Johansson, Lars Eriksson, Jonas Bergquist, Torben Rasmussen, Hans Christian Becker, Leif Hammarström, Per Ola Norrby, Björn Åkermark, Petter Persson

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Abstract

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 Ru II 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.

Original languageEnglish
Pages (from-to)3540-3548
Number of pages9
JournalInorganic Chemistry
Volume47
Issue number9
DOIs
Publication statusPublished - May 5 2008

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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    Abrahamsson, M., Lundqvist, M. J., Wolpher, H., Johansson, O., Eriksson, L., Bergquist, J., Rasmussen, T., Becker, H. C., Hammarström, L., Norrby, P. O., Åkermark, B., & Persson, P. (2008). Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands. Inorganic Chemistry, 47(9), 3540-3548. https://doi.org/10.1021/ic7019457