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Bistridentate Ruthenium(II)polypyridyl-Type Complexes with Microsecond 3MLCT State Lifetimes: Sensitizers for Rod-Like Molecular Arrays
Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Accelerator mass spectrometry group. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
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2008 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 46, 15533-15542 p.Article 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. Vol. 130, no 46, 15533-15542 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95088DOI: 10.1021/ja804890kISI: 000263311300058PubMedID: 19006410OAI: oai:DiVA.org:uu-95088DiVA: diva2:169164
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Tuning of the Excited State Properties of Ruthenium(II)-Polypyridyl Complexes
Open this publication in new window or tab >>Tuning of the Excited State Properties of Ruthenium(II)-Polypyridyl Complexes
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Processes where a molecule absorbs visible light and then converts the solar energy into chemical energy are important in many biological systems, such as photosynthesis and also in many technical applications e.g. photovoltaics. This thesis describes a part of a multidisciplinary project, aiming at a functional mimic of the natural photosynthesis, with the overall goal of production of a renewable fuel from sun and water. More specific, the thesis is focused on design and photophysical characterization of new photosensitizers, i.e. light absorbers that should be capable of transferring electrons to an acceptor and be suitable building blocks for supramolecular rod-like donor-photosensitizer-acceptor arrays.

The excited state lifetime, the excited state energy and the geometry are important properties for a photosensitizer. The work presented here describes a new strategy to obtain longer excited state lifetimes of the geometrically favorable Ru(II)-bistridentate type complexes, without a concomitant substantial decrease in excited state energy. The basic idea is that a more octahedral coordination around the Ru will lead to longer excited state lifetimes. In the first generation of new photosensitizers a 50-fold increase of the excited state lifetime was observed, going from 0.25 ns for the model complex to 15 ns for the best photosensitizer. The second generation goes another step forward, to an excited state lifetime of 810 ns. Furthermore, the third generation of new photosensitizers show excited state lifetimes in the 0.45 - 5.5 microsecond region at room temperature, a significant improvement. In addition, the third generation of photosensitizers are suitable for further symmetric attachment of electron donor and acceptor motifs, and it is shown that the favorable properties are maintained upon the attachment of anchoring groups. The reactivity of the excited state towards light-induced reactions is proved and the photostability is sufficient so the new design strategy has proven successful.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 237
Keyword
Physical chemistry, Artificial photosynthesis, Ruthenium(II), Bistridentate complexes, Excited state lifetime, Linear donor-photosenstizer-acceptor arrays, Temperature dependence, Excited state decay, Fysikalisk kemi
Identifiers
urn:nbn:se:uu:diva-7230 (URN)91-554-6707-5 (ISBN)
Public defence
2006-12-01, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30
Opponent
Supervisors
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2011-06-10Bibliographically approved
2. Beyond Classical Ruthenium(II) Polypyridyl Complexes: Photosensitizers as Building Blocks For Linear Donor-Photosensitizer-Acceptor Assemblies
Open this publication in new window or tab >>Beyond Classical Ruthenium(II) Polypyridyl Complexes: Photosensitizers as Building Blocks For Linear Donor-Photosensitizer-Acceptor Assemblies
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. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 602
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-9555 (URN)978-91-554-7408-9 (ISBN)
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

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Abrahamsson, MariaJäger, MichaelPersson, PetterBecker, Hans-ChristianJohansson, OlofHammarström, Leif

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