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Beyond Classical Ruthenium(II) Polypyridyl Complexes: Photosensitizers as Building Blocks For Linear Donor-Photosensitizer-Acceptor Assemblies
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Responsible organisation
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes ruthenium(II) polypyridyl-type complexes tailored for artificial photosynthesis. Inspired by Nature, the primary events in photosystem II are mimicked by donor-photosensitizer-acceptor (D-P-A) assemblies. The photosensitizer plays a key role in such processes, and the combination of structural and photophysical properties is essential to control the electron transfer steps. In the first part, the general requirements for photosensitizers are discussed.

The second part deals with [Ru(bpy)3]2+-benzoquinone (Q) dyads (bpy is 2,2´-bipyridine) based on an asymmetric 5,5´-bisamide substituted bpy. Rapid electron-transfer from the excited state is observed to generate the RuIII-Q- charge separated states but preliminary results show no effect of the directionality of the amide link.

In the main part, a strategy to overcome the photophysical limitations of RuII bistridentate complexes (e.g. [Ru(tpy)2]2+, tpy is 2,2´:6´,2´´-terpyridine) is explored. The prototypical [Ru(dqp)2]2+ complex (dqp is 2,6-di(quinolin-8-yl)pyridine) is synthesized which displays a 3000 ns excited state lifetime at room temperature, reversible redox chemistry and high photostability. The synthesis of 4-substituted dqp is achieved via SUZUKI coupling using 8-quinoline boronic acid or ring-formation of the central pyridine. A markedly rich Ru coordination chemistry was observed, e.g. facial and meridional isomers of [Ru(dqp)2]2+. Using a chloride-free [Ru(dqp-R)(MeCN)3]2+ intermediate allows the synthesis of heteroleptic meridional [Ru(dqp-R)(dqp-R’)]2+ (R,R’ = -H, -CO2Et, -NH2, -OMe, -Br, -PhBr, …) in high yields. The meridional complexes show long-lived luminescence (450 - 5500 ns) and reversible redox chemistry. The photochemical reactivity has been investigated in typical electron-transfer reactions, e.g. in a supramolecular P-A dyad and in a multimolecular approach using biomimetic components (Mn and Fe complexes).

The dqp ligand is further used to synthesize FeII, RhIII, cyclometallating RuII complexes and an aza-analogue of [Ru(dqp)2]2+ and is discussed in the final part. These complexes were prepared with the aim to further tune the redox properties while maintaining good photophysical properties.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2009. , p. 58
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 602
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-9555ISBN: 978-91-554-7408-9 (print)OAI: oai:DiVA.org:uu-9555DiVA, id: diva2:173246
Public defence
2009-03-20, Häggsalen, Ångström Laboratories, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-02-26 Created: 2009-02-04 Last updated: 2011-06-10Bibliographically approved
List of papers
1. Towards [Ru(bpy)3]2+-Based Linear Donor (D)-Photosensitizer (P)-Acceptor (A) Arrays: Using the 5,5´-Positions in [Ru(bpy)3]2+-Benzoquinone Dyads
Open this publication in new window or tab >>Towards [Ru(bpy)3]2+-Based Linear Donor (D)-Photosensitizer (P)-Acceptor (A) Arrays: Using the 5,5´-Positions in [Ru(bpy)3]2+-Benzoquinone Dyads
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Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-98070 (URN)
Available from: 2009-02-04 Created: 2009-02-04 Last updated: 2010-04-07Bibliographically approved
2. A 3.0 mu s room temperature excited state lifetime of a bistridentate Ru-II-polypyridine complex for rod-like molecular arrays
Open this publication in new window or tab >>A 3.0 mu s room temperature excited state lifetime of a bistridentate Ru-II-polypyridine complex for rod-like molecular arrays
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2006 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 39, p. 12616-12617Article in journal (Refereed) Published
Abstract [en]

A bistridentate RuII-polypyridine complex [Ru(bqp)2]2+ (bqp = 2,6-bis(8'-quinolinyl)pyridine) has been prepared, which has a coordination geometry much closer to a perfect octahedron than the typical Ru(terpyridine)2-type complex. Thus, the complex displays a 3.0 mus lifetime of the lowest excited metal-to-ligand charge transfer (3MLCT) state at room temperature. This is, to the best of our knowledge, the longest MLCT state lifetime reported for a RuII-polypyridyl complex at room temperature. The structure allows for the future construction of rod-like, isomer-free molecular arrays by substitution of donor and acceptor moieties on the central pyridine units. This makes it a promising photosensitizer for applications in molecular devices for artificial photosynthesis and molecular electronics.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-95087 (URN)10.1021/ja064262y (DOI)000240795000014 ()17002333 (PubMedID)
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2017-12-14Bibliographically approved
3. Synthesis and Characterization of 2,6-Di(quinolin-8-yl)pyridines: New Ligands for Bistridentate RuII Complexes with Microsecond Luminescent Lifetimes
Open this publication in new window or tab >>Synthesis and Characterization of 2,6-Di(quinolin-8-yl)pyridines: New Ligands for Bistridentate RuII Complexes with Microsecond Luminescent Lifetimes
2007 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 72, no 26, p. 10227-10230Article in journal (Refereed) Published
Abstract [en]

The synthesis of 4-substituted and 4-aryl-substituted 2,6-di(quinolin-8-yl)pyridines is described. The tridentate ligands were prepared via a palladium-catalyzed Suzuki−Miyaura cross-coupling reaction or via a one-step ring-forming reaction generating the central pyridine ring. X-ray crystal structures and 1H NMR shifts are discussed and compared to the corresponding data for a RuII bistridentate complex. Intramolecular stacking of two quinoline units in the RuII complex is suggested by 1H NMR data and also observed in the X-ray structure.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-98072 (URN)10.1021/jo7015373 (DOI)000251653000043 ()18001093 (PubMedID)
Available from: 2009-02-04 Created: 2009-02-04 Last updated: 2017-12-13Bibliographically approved
4. Bistridentate Ruthenium(II)polypyridyl-Type Complexes with Microsecond 3MLCT State Lifetimes: Sensitizers for Rod-Like Molecular Arrays
Open this publication in new window or tab >>Bistridentate Ruthenium(II)polypyridyl-Type Complexes with Microsecond 3MLCT State Lifetimes: Sensitizers for Rod-Like Molecular Arrays
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2008 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 46, p. 15533-15542Article in journal (Refereed) Published
Abstract [en]

A series of bistridentate ruthenium(II) polypyridyl-type complexes based on the novel 2,6-di(quinolin-8-yl)pyridine (dqp) ligand have been synthesized and their photophysical properties have been studied. The complexes are amenable to substitution in the 4-position of the central pyridine with conserved quasi-C2v symmetry, which allows for extension to isomer-free, rod-like molecular arrays for vectorial control of electron and energy transfer. DFT calculations performed on the parent [Ru(dqp) 2](2+) complex (1) predicted a more octahedral structure than in the typical bistridentate complex [Ru(tpy)2](2+) (tpy is 2,2':6',2"-terpyridine) thanks to the larger ligand bite angle, which was confirmed by X-ray crystallography. A strong visible absorption band, with a maximum at 491 nm was assigned to a metal-to-ligand charge transfer (MLCT) transition, based on time-dependent DFT calculations. 1 shows room temperature emission (Phi = 0.02) from its lowest excited ((3)MLCT) state that has a very long lifetime (tau = 3 micros). The long lifetime is due to a stronger ligand field, because of the more octahedral structure, which makes the often dominant activated decay via short-lived metal-centered states insignificant also at elevated temperatures. A series of complexes based on dqp with electron donating and/or accepting substituents in the 4-position of the pyridine was prepared and the properties were compared to those of 1. An unprecedented (3)MLCT state lifetime of 5.5 micros was demonstrated for the homoleptic complex based on dqpCO2Et. The favorable photosensitizer properties of 1, such as a high extinction coefficient, high excited-state energy and long lifetime, and tunable redox potentials, are maintained upon substitution. In addition, the parent complex 1 is shown to be remarkably photostable and displays a high reactivity in light-induced electron and energy transfer reactions with typical energy and electron acceptors and donors: methylviologen, tetrathiofulvalene, and 9,10-diphenylanthracene. This new class of complexes constitutes a promising starting point for the construction of linear, rod-like molecular arrays for photosensitized reactions and applications in artificial photosynthesis and molecular electronics.

Place, publisher, year, edition, pages
ACS, 2008
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-95088 (URN)10.1021/ja804890k (DOI)000263311300058 ()19006410 (PubMedID)
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2017-12-14Bibliographically approved
5. Facile synthesis of bistridentate Ru(II) complexes based on 2,6-di(quinolin-8-yl)pyridyl ligands: sensitizers with microsecond 3MLCT excited state lifetimes
Open this publication in new window or tab >>Facile synthesis of bistridentate Ru(II) complexes based on 2,6-di(quinolin-8-yl)pyridyl ligands: sensitizers with microsecond 3MLCT excited state lifetimes
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2009 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, no 7, p. 3228-3238Article in journal (Refereed) Published
Abstract [en]

Synthetic routes to meridional bistridentate ruthenium(II) complexes based on 2,6-di(quinolin-8-yl)pyridyl (dqp) ligands have been investigated. Microwave-assisted synthesis at 200 degrees C allowed the high yield (49-87%) preparation of homoleptic meridional [Ru(dqp)(2)](2+)-based complexes containing inert functional groups. Applying this protocol for the synthesis of mer-[Ru(dqp)(2)](2+) (mer-1) but lowering the temperature to 180 degrees C and shorter reaction times revealed the formation of the facial isomers cis,fac-1 and trans,fac-1 (56% and 12% yields, respectively). The facial isomers were characterized by NMR spectroscopy and X-ray diffraction analysis. In a stepwise protocol, the reaction of Ru(dqp)Cl(3) or Ru(dqp)(L)Cl(2) (L = MeCN or DMSO) and a second equivalent dqp gave mer-1 in 12-26% yields and N(5)Cl-coordinated [Ru(dqp)(2)Cl](+) (28-46%). [Ru(dqp(2))Cl](+) was photochemically, or thermally in the presence of Ag(I), converted to mer-1. By using mer-[Ru(dqp)(MeCN)(3)] (2+), which was crystallographically characterized, a wide range of homo- and heteroleptic meridional [Ru(dqp)(2)](2+)-based complexes was synthesized in up to 77% yield. The synthetic utility of meridional [Ru(dqp)(2)](2+)-based complexes as building blocks was demonstrated by palladium-catalyzed homocoupling of mer-[Ru(dqp)(dqpPhBr)](2+) to form a dinuclear complex. The redox and photophysical properties of the meridional complexes are discussed.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-98074 (URN)10.1021/ic802342t (DOI)000264759500062 ()19254036 (PubMedID)
Available from: 2009-02-04 Created: 2009-02-04 Last updated: 2017-12-13Bibliographically approved

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