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Light induced manganese oxidation and long-lived charge separation in a Mn-2(II,II)-Ru-II (bpy)(3)-acceptor triad

Borgström, Magnus; shaikh, Nizamuddin LU ; Johansson, O; Anderlund, MF; Styring, Stenbjörn LU ; Akermark, B; Magnuson, Ann LU and Hammarstrom, L (2005) In Journal of the American Chemical Society 127(49). p.17504-17515
Abstract
The photoinduced electron-transfer reactions in a Mn-2(II.II)-R-II-NDI triad (1) ([Mn-2(bpmp)(OAc)(2)](+), bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyiphenolate and OAc = acetate, R-II = trisbipyridine ruthenium(II), and NDI = naphthalenediimide) have been studied by time-resolved optical and EPR spectroscopy. Complex 1 is the first synthetically linked electron donor-sensitizer-acceptor triad in which a manganese complex plays the role of the donor. EPR spectroscopy was used to directly demonstrate the light induced formation of both products: the oxidized manganese dimer complex (Mn-2(II.III)) and the reduced naphthalenediimide (NDIcenter dot-) acceptor moieties, while optical spectroscopy was used to follow the kinetic... (More)
The photoinduced electron-transfer reactions in a Mn-2(II.II)-R-II-NDI triad (1) ([Mn-2(bpmp)(OAc)(2)](+), bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyiphenolate and OAc = acetate, R-II = trisbipyridine ruthenium(II), and NDI = naphthalenediimide) have been studied by time-resolved optical and EPR spectroscopy. Complex 1 is the first synthetically linked electron donor-sensitizer-acceptor triad in which a manganese complex plays the role of the donor. EPR spectroscopy was used to directly demonstrate the light induced formation of both products: the oxidized manganese dimer complex (Mn-2(II.III)) and the reduced naphthalenediimide (NDIcenter dot-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)(3)](2+) intermediate states and the NDIcenter dot- radical in a wide temperature range. The average lifetime of the NDI- radical is ca. 600 mu s at room temperature, which is at least 2 orders of magnitude longer than that for previously reported triads based on a [Ru(bpy)(3)](2+) photosensitizer. At 140 K, this intramolecular recombination was dramatically slowed, displaying a lifetime of 0.1-1 s, which is comparable to many of the naturally occurring charge-separated states in photosynthetic reaction centra. It was found that the long recombination lifetime could be explained by an unusually large reorganization energy (lambda approximate to 2.0 eV), due to a large inner reorganization of the manganese complex. This makes the recombination reaction strongly activated despite the large driving force (-Delta G degrees = 1.07 eV). Thus, the intrinsic properties of the manganese complex are favorable for creating a long-lived charge separation in the "Marcus normal region" also when the charge separated state energy is high. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of the American Chemical Society
volume
127
issue
49
pages
17504 - 17515
publisher
The American Chemical Society
external identifiers
  • wos:000233917500075
  • scopus:29044448014
ISSN
1520-5126
DOI
10.1021/ja055243b
language
English
LU publication?
yes
id
3e927973-d488-4998-bec6-23926e764ef8 (old id 151417)
date added to LUP
2007-07-04 14:06:43
date last changed
2017-08-20 04:15:23
@article{3e927973-d488-4998-bec6-23926e764ef8,
  abstract     = {The photoinduced electron-transfer reactions in a Mn-2(II.II)-R-II-NDI triad (1) ([Mn-2(bpmp)(OAc)(2)](+), bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyiphenolate and OAc = acetate, R-II = trisbipyridine ruthenium(II), and NDI = naphthalenediimide) have been studied by time-resolved optical and EPR spectroscopy. Complex 1 is the first synthetically linked electron donor-sensitizer-acceptor triad in which a manganese complex plays the role of the donor. EPR spectroscopy was used to directly demonstrate the light induced formation of both products: the oxidized manganese dimer complex (Mn-2(II.III)) and the reduced naphthalenediimide (NDIcenter dot-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)(3)](2+) intermediate states and the NDIcenter dot- radical in a wide temperature range. The average lifetime of the NDI- radical is ca. 600 mu s at room temperature, which is at least 2 orders of magnitude longer than that for previously reported triads based on a [Ru(bpy)(3)](2+) photosensitizer. At 140 K, this intramolecular recombination was dramatically slowed, displaying a lifetime of 0.1-1 s, which is comparable to many of the naturally occurring charge-separated states in photosynthetic reaction centra. It was found that the long recombination lifetime could be explained by an unusually large reorganization energy (lambda approximate to 2.0 eV), due to a large inner reorganization of the manganese complex. This makes the recombination reaction strongly activated despite the large driving force (-Delta G degrees = 1.07 eV). Thus, the intrinsic properties of the manganese complex are favorable for creating a long-lived charge separation in the "Marcus normal region" also when the charge separated state energy is high.},
  author       = {Borgström, Magnus and shaikh, Nizamuddin and Johansson, O and Anderlund, MF and Styring, Stenbjörn and Akermark, B and Magnuson, Ann and Hammarstrom, L},
  issn         = {1520-5126},
  language     = {eng},
  number       = {49},
  pages        = {17504--17515},
  publisher    = {The American Chemical Society},
  series       = {Journal of the American Chemical Society},
  title        = {Light induced manganese oxidation and long-lived charge separation in a Mn-2(II,II)-Ru-II (bpy)(3)-acceptor triad},
  url          = {http://dx.doi.org/10.1021/ja055243b},
  volume       = {127},
  year         = {2005},
}