Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems Yunhua Xu Stockholm University 2005 1 Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems Akademisk avhandling som för avläggande av filosofie doktorsexamen vid Stockholms Universitet, tillsammans med arbetena I-VII, offentligen kommer att försvaras i Magnélisalen, Kemiska övnings-laboratoriet, Svante Arrhenius väg 16, onsdagen den 20 april 2005, klockan 10.00. Av Yunhua Xu Avhandlingen försvaras på engelska Institutionen för organisk kemi ISBN 91-7155-034-8 pp 1-53 Arrheniuslaboratoriet Stockholm 2005 Stockholms Universitet 106 91 Stockholm Abstract Artificial systems involving water oxidation and solar cells are promising ways for the conversion of solar energy into fuels and electricity. These systems usually consist of a photosensitizer, an electron donor and / or an electron acceptor. This thesis deals with the synthesis and photoinduced electron transfer of several donor-sensitizer- acceptor supramolecular systems. The first part of this thesis describes the synthesis and properties of two novel dinuclear ruthenium complexes as electron donors to mimic the donor side reaction of Photosystem II. These two Ru2 complexes were then covalently linked to ruthenium trisbipyridine and the properties of the resulting trinuclear complexes were studied by cyclic voltammetry and transient absorption spectroscopy. The second part presents the synthesis and photoinduced electron transfer of covalently linked donor-sensitizer supramolecular systems in the presence of TiO2 as electron acceptors. Electron donors are tyrosine, phenol and their derivatives, and dinuclear ruthenium complexes. Intramolecular electron transfer from the donor to the oxidized sensitizer was observed by transient absorption spectroscopy after light 2+ excitation of the Ru(bpy)3 moiety. The potential applications of Ru2-based electron donors in artificial systems for water oxidation and solar cells are discussed. In the final part, the photoinduced interfacial electron transfer in the systems based on carotenoids and TiO2 is studied. Carotenoids are shown to act as both sensitizers and electron donors, which could be used in artificial systems to mimic the electron transfer chain in natural photosynthesis. 2 Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems Yunhua Xu Department of Organic Chemistry Stockholm University 2005 3 Doctoral Dissertation 2005 Department of Organic Chemistry Arrhenius Laboratory Stockholm University Sweden Abstract Artificial systems involving water oxidation and solar cells are promising ways for the conversion of solar energy into fuels and electricity. These systems usually consist of a photosensitizer, an electron donor and / or an electron acceptor. This thesis deals with the synthesis and photoinduced electron transfer of several donor-sensitizer- acceptor supramolecular systems. The first part of this thesis describes the synthesis and properties of two novel dinuclear ruthenium complexes as electron donors to mimic the donor side reaction of Photosystem II. These two Ru2 complexes were then covalently linked to ruthenium trisbipyridine and the properties of the resulting trinuclear complexes were studied by cyclic voltammetry and transient absorption spectroscopy. The second part presents the synthesis and photoinduced electron transfer of covalently linked donor-sensitizer supramolecular systems in the presence of TiO2 as electron acceptors. Electron donors are tyrosine, phenol and their derivatives, and dinuclear ruthenium complexes. Intramolecular electron transfer from the donor to the oxidized sensitizer was observed by transient absorption spectroscopy after light 2+ excitation of the Ru(bpy)3 moiety. The potential applications of Ru2-based electron donors in artificial systems for water oxidation and solar cells are discussed. In the final part, the photoinduced interfacial electron transfer in the systems based on carotenoids and TiO2 is studied. Carotenoids are shown to act as both sensitizers and electron donors, which could be used in artificial systems to mimic the electron transfer chain in natural photosynthesis. © Yunhua Xu ISBN 91-7155-034-8 pp 1-53 Intellecta Docusys AB, Sollentuna 4 Table of Contents List of Publications .............................................................................................................. i List of Abbreviations .......................................................................................................... ii Preface................................................................................................................................iii 1 Artificial Photosynthesis and Dye-sensitized Solar Cells............................................. 1 1.1 Introduction ........................................................................................................... 1 1.2 Natural and Artificial Photosynthesis.................................................................... 2 1.3 Dye-sensitized Solar Cells..................................................................................... 3 1.4 Donor-Sensitizer-Acceptor Systems...................................................................... 5 1.4.1 Photosensitizers............................................................................................ 6 1.4.2 Electron Donors............................................................................................ 7 1.4.3 Electron Acceptors ....................................................................................... 7 2 Synthesis and Properties of Dinuclear Ruthenium Complexes as Electron Donors..... 9 2.1 Dinuclear Ruthenium Complexes........................................................................ 10 2.1.1 Synthesis and Characterization ................................................................... 11 2.1.2 Photophysical and Electrochemical Properties ........................................... 12 2.1.3 Conclusions ................................................................................................. 14 2+ 2.2 Dinuclear Ruthenium Complexes Covalently Linked to Ru(bpy)3 .................. 15 2.2.1 Synthesis and Characterization ................................................................... 16 2.2.2 Properties of the Complexes ....................................................................... 18 2.2.3 Conclusions ................................................................................................. 22 3 Photoinduced Electron Transfers in Donor-Sensitizer-Acceptor Systems ................. 23 2+ 3.1 Tyrosine-Ru(bpy)3 Anchored to TiO2 in Colloid Solution............................... 23 3.1.1 Synthesis and Sample Preparation .............................................................. 24 3.1.2 Photophysical Properties and Photoinduced Electron Transfer .................. 26 3.1.3 Conclusions ................................................................................................. 28 2+ 3.2 Substituted Tyrosine-Ru(bpy)3 Anchored to TiO2 Films ................................. 28 3.2.1 Sample Preparation ..................................................................................... 29 3.2.2 Photoinduced Electron Transfer.................................................................. 29 3.2.3 Conclusions ................................................................................................. 31 2+ 3.3 Polyphenolate-Ru(bpy)3 in the Presence of External Acceptors ...................... 31 3.3.1 Synthesis and Properties.............................................................................. 32 3.3.2 Photoinduced Electron Transfer.................................................................. 32 3.3.3 Conclusions ................................................................................................. 33 3.4 Ru2-Ru(bpy)3 Anchored to TiO2 Film................................................................. 34 3.4.1 Photoinduced Electron Transfer.................................................................. 34 3.4.2 Conclusions ................................................................................................. 35 4 Photoinduced Electron Transfer in Supermolecules Based on Carotenoid –TiO2 ..... 37 4.1 Carotenoid Anchored to TiO2 Nanoparticles....................................................... 37 4.1.1 Synthesis...................................................................................................... 38 4.1.2 Properties and Photoinduced Electron Transfer.......................................... 38 4.1.3 Conclusions ................................................................................................. 39 4.2 Carotenoid and Pheophytin Assembled on TiO2 Surface.................................... 40 5 4.2.1 Sample Preparation ..................................................................................... 40 4.2.2 Photoinduced Electron Transfer.................................................................. 41 4.2.3 Conclusions ................................................................................................. 42 5 Concluding Remarks................................................................................................... 43 6 Supplementary Information ........................................................................................ 45 Acknowledgements..........................................................................................................