uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
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
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Show others and affiliations
2013 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 9, 5128-5137 p.Article in journal (Refereed) Published
Abstract [en]

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 quinorralines. Owing to the differences in LUMO energies, the complexes' reduction potentials differ by about 900 mV [E-1/2(1(2+/1+)) = -1.17 V, E-c,E-p(3(2+/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.

Place, publisher, year, edition, pages
2013. Vol. 52, no 9, 5128-5137 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-202924DOI: 10.1021/ic400009mISI: 000318669400050OAI: oai:DiVA.org:uu-202924DiVA: diva2:634522
Available from: 2013-07-01 Created: 2013-07-01 Last updated: 2015-07-07Bibliographically approved
In thesis
1. Synthesis of Biomimetic Systems for Proton and Electron Transfer Reactions in the Ground and Excited State
Open this publication in new window or tab >>Synthesis of Biomimetic Systems for Proton and Electron Transfer Reactions in the Ground and Excited State
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A detailed understanding of natural photosynthesis provides inspiration for the development of sustainable and renewable energy sources, i.e. a technology that is capable of converting solar energy directly into chemical fuels. This concept is called artificial photosynthesis. The work described in this thesis contains contributions to the development of artificial photosynthesis in two separate areas.

The first one relates to light harvesting with a focus on the question of how electronic properties of photosensitizers can be tuned to allow for efficient photo-induced electron transfer processes. The study is based on a series of bis(tridentate)ruthenium(II) polypyridyl complexes, the geometric properties of which make them highly appealing for the construction of linear donor-photosensitizer-acceptor arrangements for efficient vectorial photo-induced electron transfer reactions. The chromophores possess remarkably long lived 3MLCT excited states and it is shown that their excited-state oxidation strength can be altered by variations of the ligand scaffold over a remarkably large range of 900 mV.

The second area of relevance to natural and artificial photosynthesis that is discussed in this thesis relates to the coupled movement of protons and electrons. The delicate interplay between these two charged particles regulates thermodynamic and kinetic aspects in many key elementary steps of natural photosynthesis, and further studies are needed to fully understand this concept. The studies are based on redox active phenols with intramolecular hydrogen bonds to quinolines. The compounds thus bear a strong resemblance to the tyrosine/histidine couple in photosystem II, i.e. the water-plastoquinone oxidoreductase enzyme in photosynthesis. The design of the biomimetic models is such that the distance between the proton donor and acceptor is varied, enabling studies on the effect the proton transfer distance has on the rate of proton-coupled electron transfer reactions. The results of the studies have implications for the development of artificial photosynthesis, in particular in connection with redox leveling, charge accumulation, as well as electron and proton transfer.

In addition to these two contributions, the excited-state dynamics of the intramolecular hydrogen-bonded phenols was investigated, thereby revealing design principles for technological applications based on excited-state intramolecular proton transfer and photoinduced tautomerization.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 104 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1258
Solar energy conversion, artificial photosynthesis, hydrogen bonds, excited state intramolecular proton transfer, tautomerization, proton-coupled electron transfer, photosensitizer, ruthenium complex.
National Category
Organic Chemistry Physical Chemistry Inorganic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
urn:nbn:se:uu:diva-251471 (URN)978-91-554-9253-3 (ISBN)
Public defence
2015-06-12, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Available from: 2015-05-22 Created: 2015-04-19 Last updated: 2015-07-07

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Parada, Giovanny A.Lomoth, ReinerHammarström, LeifOtt, Sascha
By organisation
Molecular BiomimeticsDepartment of Chemistry - ÅngströmPhysical Chemistry
In the same journal
Inorganic Chemistry
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 479 hits
ReferencesLink to record
Permanent link

Direct link