Abstract
The photoinduced electron-transfer reactions in a Mn2 II,II-RuII-NDI triad (1) ([Mn2(bpmp)(OAc) 2]+, bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4- methylphenolate and OAc = acetate, RuII = tris-bipyridine 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 (Mn2 II,III) and the reduced naphthalenediimide (NDI .-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)3]2+ intermediate states and the NDI.- radical in a wide temperature range. The average lifetime of the NDI.- radical is ca. 600 μs 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 (λ ≈ 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 (-ΔG° = 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.
| Original language | English |
|---|---|
| Pages (from-to) | 17504-17515 |
| Number of pages | 12 |
| Journal | Journal of the American Chemical Society |
| Volume | 127 |
| Issue number | 49 |
| DOIs | |
| Publication status | Published - Dec 14 2005 |
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Light induced manganese oxidation and long-lived charge separation in a Mn2 II,II-RuII(bpy)3-acceptor triad. / Borgström, Magnus; Shaikh, Nizamuddin; Johansson, Olof; Anderlund, Magnus F.; Styring, Stenbjörn; Åkermark, Björn; Magnuson, Ann; Hammarström, Leif.
In: Journal of the American Chemical Society, Vol. 127, No. 49, 14.12.2005, p. 17504-17515.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Light induced manganese oxidation and long-lived charge separation in a Mn2 II,II-RuII(bpy)3-acceptor triad
AU - Borgström, Magnus
AU - Shaikh, Nizamuddin
AU - Johansson, Olof
AU - Anderlund, Magnus F.
AU - Styring, Stenbjörn
AU - Åkermark, Björn
AU - Magnuson, Ann
AU - Hammarström, Leif
PY - 2005/12/14
Y1 - 2005/12/14
N2 - The photoinduced electron-transfer reactions in a Mn2 II,II-RuII-NDI triad (1) ([Mn2(bpmp)(OAc) 2]+, bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4- methylphenolate and OAc = acetate, RuII = tris-bipyridine 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 (Mn2 II,III) and the reduced naphthalenediimide (NDI .-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)3]2+ intermediate states and the NDI.- radical in a wide temperature range. The average lifetime of the NDI.- radical is ca. 600 μs 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 (λ ≈ 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 (-ΔG° = 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.
AB - The photoinduced electron-transfer reactions in a Mn2 II,II-RuII-NDI triad (1) ([Mn2(bpmp)(OAc) 2]+, bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4- methylphenolate and OAc = acetate, RuII = tris-bipyridine 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 (Mn2 II,III) and the reduced naphthalenediimide (NDI .-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)3]2+ intermediate states and the NDI.- radical in a wide temperature range. The average lifetime of the NDI.- radical is ca. 600 μs 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 (λ ≈ 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 (-ΔG° = 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.
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U2 - 10.1021/ja055243b
DO - 10.1021/ja055243b
M3 - Article
VL - 127
SP - 17504
EP - 17515
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 49
ER -