| 1. |
- Lindberg, David, 1986, et al.
(författare)
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Binding of Thioflavin-T to Amyloid Fibrils Leads to Fluorescence Self-Quenching and Fibril Compaction
- 2017
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 1520-4995 .- 0006-2960. ; 56:16, s. 2170-2174
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Tidskriftsartikel (refereegranskat)abstract
- Thioflavin-T binds to and detects amyloid fibrils via fluorescence enhancement. Using a combination of linear dichroism and fluorescence spectroscopies, we report that the relation between the emission intensity and binding of thioflavin-T to insulin fibrils is nonlinear and discuss this in relation to its use in kinetic assays. We demonstrate, from fluorescence lifetime recordings, that the nonlinearity is due to thioflavin-T being sensitive to self-quenching. In addition, thioflavin-T can induce fibril compaction but not alter fibril structure. Our work underscores the photophysical complexity of thioflavin-T and the necessity of calibrating the linear range of its emission response for quantitative in vitro studies.
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| 2. |
- Fredin, Lisa, et al.
(författare)
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Excited State Dynamics of Bistridentate and Trisbidentate Ru II Complexes of Quinoline-Pyrazole Ligands
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:24, s. 16354-16363
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Tidskriftsartikel (refereegranskat)abstract
- Three homoleptic ruthenium(II) complexes, [Ru(Q3PzH)3]2+, [Ru(Q1Pz)3]2+, and [Ru(DQPz)2]2+, based on the quinoline-pyrazole ligands, Q3PzH (8-(3-pyrazole)-quinoline), Q1Pz (8-(1-pyrazole)-quinoline), and DQPz (bis(quinolinyl)-1,3-pyrazole), have been spectroscopically and theoretically investigated. Spectral component analysis, transient absorption spectroscopy, density functional theory calculations, and ligand exchange reactions with different chlorination agents reveal that the excited state dynamics for Ru(II) complexes with these biheteroaromatic ligands differ significantly from that of traditional polypyridyl complexes. Despite the high energy and low reorganization energy of the excited state, nonradiative decay dominates even at liquid nitrogen temperatures, where triplet metal-to-ligand-charge-transfer emission quantum yields range from 0.7 to 3.8%, and microsecond excited state lifetimes are observed. In contrast to traditional polypyridyl complexes where ligand exchange is facilitated by expansion of the metal-ligand bonds to stabilize a metal-centered state, photoinduced ligand exchange occurs in the bidentate complexes despite no substantial MC state population, while the tridentate complex is extremely photostable despite an activated decay route, highlighting the versatile photochemistry of nonpolypyridine ligands. © 2019 American Chemical Society.
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| 3. |
- Saavedra, Valeria, 1985, et al.
(författare)
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Evidence for Conduction Band-Mediated Two-Electron Reduction of a TiO2-Bound Catalyst Triggered by Visible Light Excitation of Co-Adsorbed Organic Dyes
- 2018
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:45, s. 25822-25828
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Tidskriftsartikel (refereegranskat)abstract
- Here, we report direct spectroscopic evidence of a visible light-induced two-electron-transfer reaction to a molecular model catalyst, facilitated by conduction band mediation. Using a simple, yet remarkably reproducible, co-sensitization approach, we anchored dyes and catalysts to mesoporous TiO2 thin films, at dye/catalyst ratios of 30:1, 15:1, and 8:1. The distinct optical spectroscopic signatures of different redox states of the catalyst used, Co-protoporphyrin IX, allows for transient absorption detection of intermediate and final photoproducts in the photoexcited co-sensitized dye-TiO2-catalyst assemblies. We show that by tuning the dye/catalyst ratios, control over whether photoexcitation results in one or two electrons being transferred to the catalyst is achieved. The two-electron-transfer process is favored by a large excess of photosensitizer compared to catalyst.
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| 4. |
- Saavedra, Valeria, 1985, et al.
(författare)
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Extending charge separation lifetime and distance in patterned dye-sensitized SnO2–TiO2 µm-thin films
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 19:34, s. 22684-22690
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Tidskriftsartikel (refereegranskat)abstract
- A simple method for the preparation of patterned dye-sensitized SnO2–TiO2 thin films, designed to prolongthe lifetime of the interfacial charge separated state is presented. Using microfluidic technology,the thin films were sensitized with the organic sensitizer D35 such that they contain SnO2–TiO2 areaswith dye and SnO2 dye-free areas at which injected electrons can be accumulated. Single wavelengthtransient absorption spectroscopy confirmed significantly extended charge separation lifetime at thedye-semiconductor interface. Sufficiently high density of injected electrons results in substantialdecrease of charge recombination rate constants (kcr); a factor of B50 compared to dye-sensitized TiO2thin films and a factor of B2000 compared to dye-sensitized SnO2 thin films. Furthermore, the potentialof this approach was confirmed by photoinduced conduction band mediated electron transfer from thedye to a model electron acceptor, Co protoporphyrin IX, which was adsorbed to the SnO2-only regions.
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| 5. |
- Sundin, Elin, 1992, et al.
(författare)
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Long-lived charge separation in dye-semiconductor assemblies: A pathway to multi-electron transfer reactions
- 2018
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 54:42, s. 5289-5298
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Tidskriftsartikel (refereegranskat)abstract
- Solar energy has the potential of providing the world with clean and storable energy. In principle, solar fuels can be generated by light absorption followed by primary charge separation and secondary charge separation to reaction centres. However this comes with several challenges, including the need for long-lived charge separation and accumulation of several charges. This Feature Article focuses on how to achieve long-lived charge separation in dye sensitized semiconductor assemblies and the way towards multi-electron transfer through conduction band mediation, aiming at solar fuel generation. Herein, we discuss various examples of how the charge separated lifetime can be extended and potential ways of achieving one or multiple electron transfer in these assemblies.
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| 6. |
- Sundin, Elin, 1992
(författare)
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Photoinduced Processes in Molecular-Inorganic Materials - Design Strategies for Control of Photophysical and Photochemical Processes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sunlight is the most abundant renewable energy resource on Earth and has the potential to provide our society with clean energy. Despite this abundancy, solar energy corresponds to only a minority of the global energy production. Two major reasons for this are the limited efficiencies of solar cells and the difficulty of storing solar energy. The work presented within this Thesis aims to investigate ways of overcoming these issues. A process called singlet fission could be utilized to increase the efficiency of solar cell. The storage issue of solar energy could be circumvented by producing fuels (i.e. solar fuels) instead of electricity from sunlight. The work presented herein has been dedicated to mechanistic studies of photo-induced processes in molecular/inorganic materials. The aim has been to gather knowledge about how the materials can be designed to obtain control of the photoinduced processes; so that one process can be favored over another. Molecular/inorganic materials were used because of their favorable characteristics compared to molecules or inorganic materials alone in terms of combining the stability of inorganic materials with the tunability of molecules. In this work, a derivative of the well-known singlet fission molecule 1,3-diphenylisobenzofuran was attached to various semiconductor films in solvents of different polarities. Studies of these materials revealed that utilizing semiconductors with a relatively low conduction band energy in a non-polar environment is favorable for achieving singlet fission followed by injection from the triplet excited state. Further, studies of molecular/semiconductor materials with both photosensitizer and catalyst molecules attached to the surfaces revealed that the charge separated lifetime between the photosensitizer and the semiconductor can be significantly extended by design of a patterned film of two different semiconductors. These studies further revealed that two-electron transfer from the conduction band to an attached molecular catalyst is possible; thus, these materials are promising for use in solar fuel generating assemblies. The results presented herein can be useful for future design of molecular/inorganic materials to achieve singlet fission as well as multi-electron transfer necessary for generating solar fuels.
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| 7. |
- Sundin, Elin, 1992, et al.
(författare)
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Singlet Fission and Electron Injection from the Triplet Excited State in Diphenylisobenzofuran-Semiconductor Assemblies: Effects of Solvent Polarity and Driving Force
- 2020
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:38 Josef Michl Festschrift, s. 20794-20805
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Tidskriftsartikel (refereegranskat)abstract
- Singlet fission has emerged as a promising way to overcome the Shockley-Queisser limit in solar energy conversion devices, and a few studies have claimed proof-of-principle results using dye-sensitized photoelectrodes. However, a detailed understanding of what factors govern the fate of the excited state on mesoporous surfaces is still lacking. Here, we have studied how the excitation progresses into singlet fission, electron injection, or formation of molecular charge separated states in diphenylisobenzofuran derivatives with flexible carbon linkers attached to nanocrystalline mesoporous ZrO2, TiO2, and SnO2 thin films. We show that singlet fission occurs for the molecule attached to ZrO2 films when the assembly is immersed in nonpolar solvents, and that singlet fission is hampered by the formation of a molecular charge separated state in more polar solvents. On TiO2 surfaces, direct electron injection from the singlet excited state outcompetes the singlet fission. Instead, triplet formation occurs via charge recombination from the conduction band of TiO2 in nonpolar solvents. When the molecule is attached to SnO2 films, singlet fission partly outcompetes electron injection from the singlet excited state and the two processes occur in parallel. Subsequent to singlet fission on SnO2, triplet injection into the conduction band of SnO2 is observed. The results presented here provide a detailed picture of the singlet fission dynamics in molecules attached to mesoporous semiconductor surfaces, demonstrating that both the semiconductor substrate as well as the environment around the molecules have a large impact, which can be useful in the design of future devices.
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| 8. |
- Sundin, Elin, 1992
(författare)
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Towards Conduction Band Mediated Multi-electron Transfer: Spectroscopic Studies of Photosensitizer-semiconductor-acceptor Assemblies
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Converting solar energy into a storable form in chemical bonds, i.e., generating solar fuels, is a promising strategy for producing renewable fuels. This however comes with several challenges that need to be solved before generation of solar fuels can become a reality. One major challenge that has been the focus of this thesis is to achieve multiple electron transfer in solar fuel assemblies. Multiple electron transfer is a requirement for solar fuel forming reactions, and for that long-lived charge separation is typically necessary. In order to achieve long-lived charge separation and multiple electron transfer, hybrid systems consisting of dye-sensitized semiconductors together with molecular catalysts have been designed and studied in this work. Two main designs have been prepared, patterned combinations of two different semiconductors and co-sensitized TiO2 films with dye and catalyst molecules co-attached to the same film. In the patterned films, a pattern of TiO2 was deposited on a substrate of SnO2. By dye-sensitization of only the TiO2-SnO2 parts, the charge separation lifetime was increased by a factor of 55 compared to evenly dye-sensitized films due to the created energy barrier for back-electron transfer. Furthermore, conduction band mediated electron transfer to a catalyst attached to the SnO2 areas was demonstrated. In the co-sensitized films, the charge separation lifetime between the dye and TiO2 was increased by one order of magnitude for samples with the highest concentration of catalyst. By tuning the relative ratio of dye and catalyst to a large excess of dye, efficient conduction band mediated two-electron transfer was demonstrated by visible light excitation of the dye.
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| 9. |
- Sundin, Elin, 1992, et al.
(författare)
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Two-colour photoswitching in photoresponsive inorganic thin films
- 2021
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Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 2:7, s. 2328-2333
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Tidskriftsartikel (refereegranskat)abstract
- Herein we report the first example of an inorganic photochromic material that allows for spatial addressability. We designed a photoresponsive thin film based on a ruthenium sulfoxide complex, [Ru(deeb)2PySO-iPr]2+, which was immobilized onto a mesoporous ZrO2 surface. The resulting material allows for all-optical detection and shows reversible, selective, photochromic behavior that can be cycled back and forth. The photosiomerization quantum yield is lower on the film than in solution which is attributed to a combination of the immobilization and steric hindrance by molecules in close proximity as evident from a surface coverage dependence of the photoisomerization quantum yield. The results reported here provide an important step towards inorganic photoswitchable materials.
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