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Single and Accumulative Electron Transfer – Prerequisites for Artificial Photosynthesis
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photoinduced electron transfer is involved in a number of photochemical and photobiological processes. One example of this is photosynthesis, where the absorption of sunlight leads to the formation of charge-separated states by electron transfer. The redox equivalents built up by successive photoabsorption and electron transfer is further used for the oxidation of water and reduction of carbon dioxide to sugars. The work presented in this thesis is part of an interdisciplinary effort aiming at a functional mimic of photosynthesis. The goal of this project is to utilize sunlight to produce renewable fuels from sun and water. Specifically, this thesis concerns photoinduced electron transfer in donor(D)-photosensitizer(P)-acceptor(A) systems, in mimic of the primary events of photosynthesis.

The absorption of a photon typically leads to transfer of a single electron, i.e., charge separation to produce a single electron-hole pair. This fundamental process was studied in several molecular systems. The purpose of these studies was optimization of single electron transfer as to obtain charge separation in high yields, with minimum losses to competing photoreactions such as energy transfer. Also, the lifetime of the charge separated state and the confinement of the electron and hole in three-dimensional space are important in practical applications. This led us to explore molecular motifs for linear arrays based on Ru(II)bis-tridentate and Ru(II)tris-bidentate complexes.

The target multi-electron catalytic reactions of water-splitting and fuel production require a build-up of redox equivalents upon successive photoexcitation and electron transfer events. The possibilities and challenges associated with such processes in molecular systems were investigated. One of the studied systems was shown to accumulate two electrons and two holes upon two successive excitations, without sacrificial redox agents and with minimum yield losses. From these studies, we have gained better understanding of the obstacles associated with step-wise photoaccumulation of charge and how to overcome them.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 735
Keywords [en]
Artificial photosynthesis, Photoinduced charge separation, Electron transfer, Energy transfer, Accumulative electon transfer, Donor-acceptor, Ruthenium, Linear arrays
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
URN: urn:nbn:se:uu:diva-122206ISBN: 978-91-554-7791-2 (print)OAI: oai:DiVA.org:uu-122206DiVA, id: diva2:309498
Public defence
2010-05-21, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-04-28 Created: 2010-04-07 Last updated: 2011-03-01Bibliographically approved
List of papers
1. How Close Can You Get?: Studies of Ultrafast Light-Induced Processes in Ruthenium-[60] Fullerene Dyads with Short Pyrazolino and Pyrrolidino Links
Open this publication in new window or tab >>How Close Can You Get?: Studies of Ultrafast Light-Induced Processes in Ruthenium-[60] Fullerene Dyads with Short Pyrazolino and Pyrrolidino Links
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2008 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 47, no 16, p. 7286-7294Article in journal (Refereed) Published
Abstract [en]

Two pyrazoline- and one pyrrolidine-bridged Ru(II)bipyridine-[60]fullerene dyads have been prepared and studied by ultrafast time-resolved spectroscopy. A silver-assisted synthesis route, in which Ag(I) removes the chlorides from the precursor complex Ru(bpy)(2)Cl-2 facilitates successful coordination of the [60]fullerene-substituted third ligand. Upon light excitation of the ruthenium moiety, the emission was strongly quenched by the fullerene. The main quenching mechanism is an exceptionally fast direct energy transfer (k(obs) > , 1 x 10(12) s(-1) in the pyrazoline-bridged dyads), resulting in population of the lowest excited triplet state of fullerene. No evidence for electron transfer was found, despite the extraordinarily short donor-acceptor distance that could kinetically favor that process. The observations have implications on the ongoing development of devices built from Ru-polypyridyl complexes and nanostructured carbon, such as C-60 or nanotubes.

National Category
Other Basic Medicine
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-87346 (URN)10.1021/ic800168d (DOI)000258332900030 ()
Available from: 2008-10-07 Created: 2008-10-07 Last updated: 2018-01-12Bibliographically approved
2. Vectorial Electron Transfer in Donor-Photosensitizer-Acceptor Triads Based on Novel Bis-tridentate Ruthenium Polypyridyl Complexes
Open this publication in new window or tab >>Vectorial Electron Transfer in Donor-Photosensitizer-Acceptor Triads Based on Novel Bis-tridentate Ruthenium Polypyridyl Complexes
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2010 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 9, p. 2830-2842Article in journal (Refereed) Published
Abstract [en]

The first examples of rodlikedonor–photosensitizer–acceptor arrays based on bis-2,6-di(quinolin-8-yl)pyridineRuII complexes 1a and 3a for photoinduced electron transfer have been synthesized and investigated. The complexes are synthesized in a convergent manner and are isolated as linear, single isomers. Time-resolved absorption spectroscopy reveals long-lived, photoinduced charge-separated states(tCSS (1a)=140 ns, tCSS (3a)=200 ns) formed by stepwise electron transfer.The overall yields of charge separation (Yield 50% for complex 1a and Yield 95% for complex 3a) are unprecedented for bis-tridentate RuII polypyridyl complexes.This is attributed to the longlived excited state of the [Ru(dqp)2]2+ complex combined with fast electron transfer from the donor moiety following the initial charge separation. The rodlike arrangement of donor and acceptor gives controlled, vectorial electron transfer, free from the complications of stereoisomeric diversity. Thus, such arrays provide an excellent system for the study of photoinduced electron transfer and, ultimately, the harvesting of solar energy.

Place, publisher, year, edition, pages
Weinhem: Wiley-VCH, 2010
Keywords
donor-acceptor systems, electron transfer, photochemistry, ruthenium, tridentate ligands
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-113609 (URN)10.1002/chem.200902716 (DOI)000275943000024 ()20087914 (PubMedID)
Available from: 2010-03-22 Created: 2010-02-01 Last updated: 2017-12-12Bibliographically approved
3. 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
4. Double-pulse Excitation of a Mn2-Ru(II)-Naphthalenediimide Triad: Challenges for Accumulative Electron Transfer
Open this publication in new window or tab >>Double-pulse Excitation of a Mn2-Ru(II)-Naphthalenediimide Triad: Challenges for Accumulative Electron Transfer
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(English)Manuscript (preprint) (Other academic)
National Category
Other Basic Medicine
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
urn:nbn:se:uu:diva-113613 (URN)
Available from: 2010-04-07 Created: 2010-02-01 Last updated: 2018-01-12
5. Accumulative charge separation inspired by photosynthesis
Open this publication in new window or tab >>Accumulative charge separation inspired by photosynthesis
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2010 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 51, p. 17977-17979Article in journal (Refereed) Published
Abstract [en]

Molecular systems that follow the functional principles of photosynthesis have attracted increasing attention as a method for the direct production of solar fuels. This could give a major carbon-neutral energy contribution to our future society. An outstanding challenge in this research is to couple the light-induced charge separation (which generates a single electron-hole pair) to the multielectron processes of water oxidation and fuel generation. New design considerations are needed to allow for several cycles of photon absorption and charge separation of a single artificial photosystem. Here we demonstrate a molecular system with a regenerative photosensitizer that shows two successive events of light-induced charge separation, leading to high-yield accumulation of redox equivalents on single components without sacrificial agents.

National Category
Chemical Sciences
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
urn:nbn:se:uu:diva-122184 (URN)10.1021/ja104809x (DOI)000285818700001 ()21138258 (PubMedID)
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2017-12-12Bibliographically approved
6. Multiple Excitation Studies of Ru(II)polypyridyl-Oligotriarylamine Dye-Nanocrystalline TiO2 Systems for Photoinduced Charge Accumulation
Open this publication in new window or tab >>Multiple Excitation Studies of Ru(II)polypyridyl-Oligotriarylamine Dye-Nanocrystalline TiO2 Systems for Photoinduced Charge Accumulation
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
urn:nbn:se:uu:diva-122185 (URN)
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-04-07

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