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

Abrahamsson, Maria; Lundqvist, Maria J.; Wolpher, Henriette; Johansson, Olof; Eriksson, Lars; Bergquist, Jonas; Rasmussen, Torben; Becker, Hans-Christian; Hammarstrom, Leif and Norrby, Per-Ola, et al. (2008) In Inorganic Chemistry 47(9). p.3540-3548
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 Ru-II complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding... (More)
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 Ru-II 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 Ru-II 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 ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II 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 (MLCT)-M-3 states to short-lived (MC)-M-3 states. (Less)
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publishing date
type
Contribution to journal
publication status
published
subject
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Inorganic Chemistry
volume
47
issue
9
pages
3540 - 3548
publisher
The American Chemical Society
external identifiers
  • wos:000255380500018
  • scopus:44149100244
ISSN
1520-510X
DOI
10.1021/ic7019457
language
English
LU publication?
yes
id
dfe805d9-e5ad-4ab0-88c1-2615f66d4ac6 (old id 1203712)
date added to LUP
2008-09-17 10:40:51
date last changed
2017-10-22 03:51:15
@article{dfe805d9-e5ad-4ab0-88c1-2615f66d4ac6,
  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 Ru-II 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 Ru-II 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 ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II 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 (MLCT)-M-3 states to short-lived (MC)-M-3 states.},
  author       = {Abrahamsson, Maria and Lundqvist, Maria J. and Wolpher, Henriette and Johansson, Olof and Eriksson, Lars and Bergquist, Jonas and Rasmussen, Torben and Becker, Hans-Christian and Hammarstrom, Leif and Norrby, Per-Ola and Åkemark, Björn and Persson, Petter},
  issn         = {1520-510X},
  language     = {eng},
  number       = {9},
  pages        = {3540--3548},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl Ligands},
  url          = {http://dx.doi.org/10.1021/ic7019457},
  volume       = {47},
  year         = {2008},
}