Tuning the electronics of bis(tridentate)ruthenium(II) complexes with long-lived excited states

Modifications to the ligand skeleton beyond classical electron donor or electron withdrawing group decorations

Giovanny A. Parada, Lisa A. Fredin, Marie Pierre Santoni, Michael Jäger, Reiner Lomoth, Leif Hammarström, Olof Johansson, Petter Persson, Sascha Ott

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

A series of homoleptic bis(tridentate) [Ru(L)2]2+ (1, 3) and heteroleptic [Ru(L)(dqp)]2+ complexes (2, 4) [L = dqxp (1, 2) or dNinp (3, 4); dqxp = 2,6-di(quinoxalin-5-yl)pyridine, dNinp = 2,6-di(N-7-azaindol-1-yl)pyridine, dqp = 2,6-di(quinolin-8-yl)pyridine] was prepared and in the case of 2 and 4 structurally characterized. The presence of dqxp and dNinp in 1-4 result in anodically shifted oxidation potentials of the Ru3+/2+ couple compared to that of the archetypical [Ru(dqp) 2]2+ (5), most pronounced for [Ru(dqxp)2] 2+ (1) with a shift of +470 mV. These experimental findings are corroborated by DFT calculations, which show contributions to the complexes HOMOs by the polypyridine ligands, thereby stabilizing the HOMOs and impeding electron extraction. Complex 3 exhibits an unusual electronic absorption spectrum with its lowest energy maximum at 382 nm. TD-DFT calculations suggest that this high-energy transition is caused by a localization of the LUMO on the central pyridine fragments of the dNinp ligands in 3, leaving the lateral azaindole units merely spectator fragments. The opposite is the case in 1, where the LUMO experiences large stabilization by the lateral quinoxalines. Owing to the differences in LUMO energies, the complexes reduction potentials differ by about 900 mV [E1/2(12+/1+) = -1.17 V, E c,p(32+/1+) = -2.06 V vs Fc+/0]. As complexes 1-4 exhibit similar excited state energies of around 1.80 V, the variations of the lateral heterocycles allow the tuning of the complexes excited state oxidation strengths over a range of 900 mV. Complex 1 is the strongest excited state oxidant of the series, exceeding even [Ru(bpy)3]2+ by more than 200 mV. At room temperature, complex 3 is nonemissive, whereas complexes 1, 2, and 4 exhibit excited state lifetimes of 255, 120, and 1570 ns, respectively. The excited state lifetimes are thus somewhat shortened compared to that of 5 (3000 ns) but still acceptable to qualify the complexes as photosensitizers in light-induced charge-transfer schemes, especially for those that require high oxidative power.

Original languageEnglish
Pages (from-to)5128-5137
Number of pages10
JournalInorganic Chemistry
Volume52
Issue number9
DOIs
Publication statusPublished - May 6 2013

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Ruthenium
musculoskeletal system
Excited states
ruthenium
Electronic equipment
Tuning
tuning
Ligands
pyridines
ligands
Electrons
quinoxalines
Quinoxalines
electronics
excitation
electrons
Discrete Fourier transforms
fragments
life (durability)
Oxidation

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Tuning the electronics of bis(tridentate)ruthenium(II) complexes with long-lived excited states : Modifications to the ligand skeleton beyond classical electron donor or electron withdrawing group decorations. / Parada, Giovanny A.; Fredin, Lisa A.; Santoni, Marie Pierre; Jäger, Michael; Lomoth, Reiner; Hammarström, Leif; Johansson, Olof; Persson, Petter; Ott, Sascha.

In: Inorganic Chemistry, Vol. 52, No. 9, 06.05.2013, p. 5128-5137.

Research output: Contribution to journalArticle

Parada, Giovanny A. ; Fredin, Lisa A. ; Santoni, Marie Pierre ; Jäger, Michael ; Lomoth, Reiner ; Hammarström, Leif ; Johansson, Olof ; Persson, Petter ; Ott, Sascha. / Tuning the electronics of bis(tridentate)ruthenium(II) complexes with long-lived excited states : Modifications to the ligand skeleton beyond classical electron donor or electron withdrawing group decorations. In: Inorganic Chemistry. 2013 ; Vol. 52, No. 9. pp. 5128-5137.
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title = "Tuning the electronics of bis(tridentate)ruthenium(II) complexes with long-lived excited states: Modifications to the ligand skeleton beyond classical electron donor or electron withdrawing group decorations",
abstract = "A series of homoleptic bis(tridentate) [Ru(L)2]2+ (1, 3) and heteroleptic [Ru(L)(dqp)]2+ complexes (2, 4) [L = dqxp (1, 2) or dNinp (3, 4); dqxp = 2,6-di(quinoxalin-5-yl)pyridine, dNinp = 2,6-di(N-7-azaindol-1-yl)pyridine, dqp = 2,6-di(quinolin-8-yl)pyridine] was prepared and in the case of 2 and 4 structurally characterized. The presence of dqxp and dNinp in 1-4 result in anodically shifted oxidation potentials of the Ru3+/2+ couple compared to that of the archetypical [Ru(dqp) 2]2+ (5), most pronounced for [Ru(dqxp)2] 2+ (1) with a shift of +470 mV. These experimental findings are corroborated by DFT calculations, which show contributions to the complexes HOMOs by the polypyridine ligands, thereby stabilizing the HOMOs and impeding electron extraction. Complex 3 exhibits an unusual electronic absorption spectrum with its lowest energy maximum at 382 nm. TD-DFT calculations suggest that this high-energy transition is caused by a localization of the LUMO on the central pyridine fragments of the dNinp ligands in 3, leaving the lateral azaindole units merely spectator fragments. The opposite is the case in 1, where the LUMO experiences large stabilization by the lateral quinoxalines. Owing to the differences in LUMO energies, the complexes reduction potentials differ by about 900 mV [E1/2(12+/1+) = -1.17 V, E c,p(32+/1+) = -2.06 V vs Fc+/0]. As complexes 1-4 exhibit similar excited state energies of around 1.80 V, the variations of the lateral heterocycles allow the tuning of the complexes excited state oxidation strengths over a range of 900 mV. Complex 1 is the strongest excited state oxidant of the series, exceeding even [Ru(bpy)3]2+ by more than 200 mV. At room temperature, complex 3 is nonemissive, whereas complexes 1, 2, and 4 exhibit excited state lifetimes of 255, 120, and 1570 ns, respectively. The excited state lifetimes are thus somewhat shortened compared to that of 5 (3000 ns) but still acceptable to qualify the complexes as photosensitizers in light-induced charge-transfer schemes, especially for those that require high oxidative power.",
author = "Parada, {Giovanny A.} and Fredin, {Lisa A.} and Santoni, {Marie Pierre} and Michael J{\"a}ger and Reiner Lomoth and Leif Hammarstr{\"o}m and Olof Johansson and Petter Persson and Sascha Ott",
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T1 - Tuning the electronics of bis(tridentate)ruthenium(II) complexes with long-lived excited states

T2 - Modifications to the ligand skeleton beyond classical electron donor or electron withdrawing group decorations

AU - Parada, Giovanny A.

AU - Fredin, Lisa A.

AU - Santoni, Marie Pierre

AU - Jäger, Michael

AU - Lomoth, Reiner

AU - Hammarström, Leif

AU - Johansson, Olof

AU - Persson, Petter

AU - Ott, Sascha

PY - 2013/5/6

Y1 - 2013/5/6

N2 - A series of homoleptic bis(tridentate) [Ru(L)2]2+ (1, 3) and heteroleptic [Ru(L)(dqp)]2+ complexes (2, 4) [L = dqxp (1, 2) or dNinp (3, 4); dqxp = 2,6-di(quinoxalin-5-yl)pyridine, dNinp = 2,6-di(N-7-azaindol-1-yl)pyridine, dqp = 2,6-di(quinolin-8-yl)pyridine] was prepared and in the case of 2 and 4 structurally characterized. The presence of dqxp and dNinp in 1-4 result in anodically shifted oxidation potentials of the Ru3+/2+ couple compared to that of the archetypical [Ru(dqp) 2]2+ (5), most pronounced for [Ru(dqxp)2] 2+ (1) with a shift of +470 mV. These experimental findings are corroborated by DFT calculations, which show contributions to the complexes HOMOs by the polypyridine ligands, thereby stabilizing the HOMOs and impeding electron extraction. Complex 3 exhibits an unusual electronic absorption spectrum with its lowest energy maximum at 382 nm. TD-DFT calculations suggest that this high-energy transition is caused by a localization of the LUMO on the central pyridine fragments of the dNinp ligands in 3, leaving the lateral azaindole units merely spectator fragments. The opposite is the case in 1, where the LUMO experiences large stabilization by the lateral quinoxalines. Owing to the differences in LUMO energies, the complexes reduction potentials differ by about 900 mV [E1/2(12+/1+) = -1.17 V, E c,p(32+/1+) = -2.06 V vs Fc+/0]. As complexes 1-4 exhibit similar excited state energies of around 1.80 V, the variations of the lateral heterocycles allow the tuning of the complexes excited state oxidation strengths over a range of 900 mV. Complex 1 is the strongest excited state oxidant of the series, exceeding even [Ru(bpy)3]2+ by more than 200 mV. At room temperature, complex 3 is nonemissive, whereas complexes 1, 2, and 4 exhibit excited state lifetimes of 255, 120, and 1570 ns, respectively. The excited state lifetimes are thus somewhat shortened compared to that of 5 (3000 ns) but still acceptable to qualify the complexes as photosensitizers in light-induced charge-transfer schemes, especially for those that require high oxidative power.

AB - A series of homoleptic bis(tridentate) [Ru(L)2]2+ (1, 3) and heteroleptic [Ru(L)(dqp)]2+ complexes (2, 4) [L = dqxp (1, 2) or dNinp (3, 4); dqxp = 2,6-di(quinoxalin-5-yl)pyridine, dNinp = 2,6-di(N-7-azaindol-1-yl)pyridine, dqp = 2,6-di(quinolin-8-yl)pyridine] was prepared and in the case of 2 and 4 structurally characterized. The presence of dqxp and dNinp in 1-4 result in anodically shifted oxidation potentials of the Ru3+/2+ couple compared to that of the archetypical [Ru(dqp) 2]2+ (5), most pronounced for [Ru(dqxp)2] 2+ (1) with a shift of +470 mV. These experimental findings are corroborated by DFT calculations, which show contributions to the complexes HOMOs by the polypyridine ligands, thereby stabilizing the HOMOs and impeding electron extraction. Complex 3 exhibits an unusual electronic absorption spectrum with its lowest energy maximum at 382 nm. TD-DFT calculations suggest that this high-energy transition is caused by a localization of the LUMO on the central pyridine fragments of the dNinp ligands in 3, leaving the lateral azaindole units merely spectator fragments. The opposite is the case in 1, where the LUMO experiences large stabilization by the lateral quinoxalines. Owing to the differences in LUMO energies, the complexes reduction potentials differ by about 900 mV [E1/2(12+/1+) = -1.17 V, E c,p(32+/1+) = -2.06 V vs Fc+/0]. As complexes 1-4 exhibit similar excited state energies of around 1.80 V, the variations of the lateral heterocycles allow the tuning of the complexes excited state oxidation strengths over a range of 900 mV. Complex 1 is the strongest excited state oxidant of the series, exceeding even [Ru(bpy)3]2+ by more than 200 mV. At room temperature, complex 3 is nonemissive, whereas complexes 1, 2, and 4 exhibit excited state lifetimes of 255, 120, and 1570 ns, respectively. The excited state lifetimes are thus somewhat shortened compared to that of 5 (3000 ns) but still acceptable to qualify the complexes as photosensitizers in light-induced charge-transfer schemes, especially for those that require high oxidative power.

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