| 1. |
- Canton, S. E., et al.
(författare)
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Watching the dynamics of electrons and atoms at work in solar energy conversion
- 2015
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Ingår i: Faraday discussions. - : Royal Society of Chemistry. - 1359-6640 .- 1364-5498. ; 185, s. 51-68
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Tidskriftsartikel (refereegranskat)abstract
- The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt dyads, which belong to the large family of donor-bridge-acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray
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| 2. |
- Eliasson, Nora, et al.
(författare)
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Ultrafast Dynamics in Cu-Deficient CuInS2 Quantum Dots : SubBandgap Transitions and Self-Assembled Molecular Catalysts
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 14751-14764
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties of Cu-deficient Cu01.2In1Sx quantum dots synthesized through a facile aqueous-based procedure have been investigated. Transient absorption experiments were carried out probing in the UV-vis, near-IR, and mid-IR regions, with the aim to (i) study the photophysical properties of the quantum dots and (ii) monitor kinetics of electron transfer to a molecular catalyst. When pumping subbandgap transitions, negative (bleach) signals were observed that were spectrally and kinetically distinct from those observed with bandgap pump wavelengths. Herein, these distinct contributions are suggested to result from the overlapping bleaching of state filling electrons and trapped holes. Such an interpretation highlights the importance of considering the hole-contributions to the bleach for the proper determination of carrier kinetics in similar systems. A model complex of the [Fe-2]-hydrogenase active site was introduced to explore the potential of the quantum dots as photosensitizers for molecular catalysts. The quantum dot photoluminescence was quenched upon catalyst addition, and direct evidence of the singly reduced catalyst was found by transient absorption in the UV-vis and mid-IR. The catalyst accepted reducing equivalents on a subpicosecond time scale upon photoexcitation of the quantum dots, despite no covalent linking chemistry being applied. This implies that charge transfer is not limited by diffusion rates, thus confirming the presence of spontaneous quantum dot and catalyst self-assembly.
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| 3. |
- Lissau, Jonas Sandby, et al.
(författare)
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Photon Upconversion from Chemically Bound Triplet Sensitizers and Emitters on Mesoporous ZrO2 : Implications for Solar Energy Conversion
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:46, s. 25792-25806
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Tidskriftsartikel (refereegranskat)abstract
- Photon upconversion by sensitized triplet-triplet annihilation (UC-STTA) is studied in systems with triplet sensitizers and emitter molecules cochemisorbed onto nanostructured ZrO2 films. UC-STTA is a promising strategy to overcome the Shockley-Queisser efficiency limit of single-threshold solar cells. The dye-loaded mesoporous ZrO2 films studied herein allow high molecular densities and are good proxy systems for the study of photophysics relevant to dye-sensitized solar cells. Two sensitizer/emitter dye pairs are studied: platinum(II) deuteroporphyrin IX dicarboxylic acid/4,4'-(10-(anthracene-9,10-diyl)dibenzoic acid and platinum(II) deuteroporphyrin IX dimethyl ester/methyl 4-(10-(p-tolyl)anthracen-9-yl)benzoate. Both dye pairs are closely related to the standard UC-STTA molecular pair platinum(II) octaethylporphyrin (PtOEP)/9,10-diphenylanthracene (DPA). By chemically anchoring the upconverting dye pairs onto ZrO2 films a significant improvement in UC-STTA efficiency is achieved with respect to previously studied cophysisorbed PtOEP/DPA. Controlled variation of the sensitizer/emitter dye ratios onto the surface shows that new energy loss mechanisms appear at high sensitizer surface coverage. Spectral signatures of porphyrin aggregates suggest separate sensitizer domains form, which limits the triplet sensitization of emitter molecules. The nanosecond time scale rise and decay of the observed UC emission are likely linked to the sample stability over time; UC emission is observed 1 year after sample preparation. These are promising properties for the application of this type of system for solar energy conversion.
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| 4. |
- Bagnall, Andrew J.
(författare)
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Novel electrode and photoelectrode materials for hydrogen production based on molecular catalysts
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The PhD project focussed on the application of a cobalt tetraazamacrocyclic complex, in the literature commonly referred to as [Co(CR)Cl2]+ as a molecular catalyst for the hydrogen evolution reaction (HER). This was within the broader scope of the EU MSCA H2020 ITN ‘eSCALED’ project, which primarily aimed to create artificial leaf devices for the storage of solar energy in chemical fuels and, as part of this, sought the development of novel bio-inspired and scalable materials. This included researching molecular catalysts without platinum group metals (PGMs) currently relied upon in commercial technology.Three main projects were pursued: firstly, studies of the mechanism of the catalyst itself under organic electrocatalytic conditions. Catalytic intermediates were generated and identified using spectroscopy (UV-vis, NMR, EPR) and the catalytic behaviour was followed with electrochemical techniques. An ECEC mechanism with a rate-determining second protonation step associated with the release of H2 was identified, noting in particular an initial protonation step on the macrocycle at the Co(II) state that was hypothesised to involve the macrocycle amine group acting as a proton relay under the investigated conditions.Secondly, a new synthetic strategy towards novel derivatives of [Co(CR)Cl2]+ was developed to prepare a derivative for anchoring onto sp2-carbon surfaces by pi-stacking interactions. The immobilised catalyst was studied by electrochemical methods and compared with another derivative from collaborators at ICIQ, showing that both derivatives work as heterogenised electrocatalysts for the HER with high faradaic efficiencies and good stability over one hour at pH 2 and especially pH 7, but one derivative displays higher current densities and stability, invoking some consideration of rational design principles for modifying molecular catalysts.Thirdly, studies of a photocatalytic system made up of copper indium sulfide quantum dots (CuInS2 QDs) as a photosensitiser with either [Co(CR)Cl2]+ or its benzoic acid-functionalised derivative were carried out in ascorbate buffer, focussing on the photocatalytic performance and electron transfer (ET) processes between the CuInS2 QDs and the catalyst to explain the remarkable activity and robustness reported for closely related systems. CuInS2 QDs modified to have a ‘hybrid-passivation’ ligand system for compatibility with NiO films were used. Rapid QD-catalyst ET processes were noted for both catalysts. A static binding model with a strong binding equilibrium was adapted for the system, applying a Poisson distribution. This prompts a reconsideration of the importance of anchoring groups for QD-catalyst ET efficiency in solution.
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| 5. |
- Howe, Andrew, 1995-
(författare)
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Immobilisation of Ru-Based Molecular Catalysts for Electrochemical Water Oxidation
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial photosynthesis requires catalysts for efficient and selective conversions of small molecules. Molecular catalysts are advantageous to use in these instances as they offer precise control over chemical reactivity. They are synthetically tuneable, and their catalytic mechanisms are often well documented and more readily understood than those of solid-state catalysts. In this thesis, the synthetic incorporation of molecular catalysts into heterogenised molecular anodes for water oxidation are evaluated. The catalysts are incorporated as structural linkers into porous metal-organic framework (MOF) structures, and as coordination oligomers stacked onto graphitic surfaces. The preparation of MOF/molecular catalyst hybrid materials of two topologies, UiO (UiO = Universitet i Oslo) and NU-1000 (NU = Northwestern University), were investigated. Multiple synthetic methods for the incorporation of molecular ruthenium-based catalysts into MOFs were examined in papers I and II. In paper III of this thesis, a Ru-bda type molecular complex was successfully used in the solvothermal synthesis of a new MOF. The resulting material is the first of its kind that is built exclusively from molecular water oxidation catalyst linkers. It is shown that MOF incorporation greatly enhances the structural stability of the catalyst linker in chemical water oxidation experiments, giving rise to higher turnover numbers compared to that of a homogenous reference system. Finally, paper IV describes a stable and inert molecular ruthenium complex, which possesses a flexible adaptative multidentate equatorial (FAME) type equatorial ligand with a carbanion on the equatorial ligand that forms a C-Ru bond. This molecular complex is studied in homogeneous phase, and subsequently incorporated into a coordination oligomer, which can be activated for water oxidation catalysis. This finding broadens the field of molecular catalysis significantly, and proves that supramolecular interactions can be used to promote electrocatalysis in complexes which are otherwise too inert and stable to engage in electrocatalytic reactions.
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| 6. |
- Parada, Giovanny A.
(författare)
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Synthesis of Biomimetic Systems for Proton and Electron Transfer Reactions in the Ground and Excited State
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Castner, Ashleigh T., et al.
(författare)
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Microscopic Insights into Cation-Coupled Electron HoppingTransport in a Metal-Organic Framework br
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:13, s. 5910-5920
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Tidskriftsartikel (refereegranskat)abstract
- Electron transport through metal-organic frameworks by ahopping mechanism between discrete redox active sites is coupled to diffusion-migration of charge-balancing counter cations. Experimentally determinedapparent diffusion coefficients,Deapp, that characterize this form of chargetransport thus contain contributions from both processes. While this is wellestablished for MOFs, microscopic descriptions of this process are largelylacking. Herein, we systematically lay out different scenarios for cation-coupledelectron transfer processes that are at the heart of charge diffusion throughMOFs. Through systematic variations of solvents and electrolyte cations, it isshown that theDeappfor charge migration through a PIZOF-type MOF,Zr(dcphOH-NDI) that is composed of redox-active naphthalenediimide(NDI) linkers, spans over 2 orders of magnitude. More importantly, however,the microscopic mechanisms for cation-coupled electron propagation arecontingent on differing factors depending on the size of the cation and its propensity to engage in ion pairs with reduced linkers,either non-specifically or in defined structural arrangements. Based on computations and in agreement with experimental results, weshow that ion pairing generally has an adverse effect on cation transport, thereby slowing down charge transport. In Zr(dcphOH-NDI), however, specific cation-linker interactions can open pathways for concerted cation-coupled electron transfer processes thatcan outcompete limitations from reduced cationflux.
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| 8. |
- D'Imperio, Nicolas Daniele, 1991-
(författare)
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Olefins from carbonyls : Development of new phosphorus-based cross-coupling reactions
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Olefins, compounds containing C=C double bonds, are omnipresent in nature and serve as useful starting materials for various chemical modifications. Olefins are of crucial importance in Medicinal Chemistry and are also present in essential objects like dyes, polymers and plastics. Thus, developing methodologies for synthesizing olefins is at the heart of Organic Chemistry.In this regard, many reactions have been developed over the years for the production of olefins from different starting materials. To date only one reaction, namely the McMurry coupling, is available for constructing olefins from two carbonyls. This reaction is frequently applied in an academic context, but suffers many drawbacks that limit its wider use. This thesis offers innovative phosphorus-based methodologies for coupling two carbonyls into olefins. All the methods presented herein are based on a one-pot sequence in which a first carbonyl is transformed into a phosphaalkene (P=C double bond containing molecule) which, upon activation, reacts with a second carbonyl with formation of desired alkenes.The first two chapters of this thesis give a general overview on literature protocols for the formation of olefins, along with a comparison between P=C and C=C double bonds containing molecules.The third chapter is dedicated to the presentation of a new potential phosphorus-based coupling reagent. The studies presented in this chapter set the basis for the development of a new cross-coupling reaction of aldehydes to olefins.In the fourth chapter a new method for the one-pot synthesis of disubstituted alkenes from aldehydes is presented. The reactivity of phosphaalkene intermediates proved to be crucial in determining the reaction scope of the process. In the fifth chapter, a closer look into the E-Z stereoselectivity of the protocol is described.The following two chapters deal with more reactive phosphaalkenes. Studies on their chemical properties showed to be fundamental for developing an unprecedent cross-coupling of ketones and aldehydes to trisubstituted alkenes.In summary, this thesis represents the development of new phosphorus-based cross-couplings of carbonyls to olefins. Protocols for the stereoselective synthesis of disubstituted alkenes from two aldehydes, and trisubstituted olefins from ketones and aldehydes are presented. These innovative methodologies offer precious alternatives to the McMurry coupling.
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| 9. |
- Karnahl, Michael, et al.
(författare)
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Structural and spectroscopic characterization of tetranuclear iron complexes containing a (P2N2Ph)-N-R bridge
- 2012
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Ingår i: Journal of coordination chemistry (Print). - : Informa UK Limited. - 0095-8972 .- 1029-0389 .- 1026-7441. ; 65:15, s. 2713-2723
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Tidskriftsartikel (refereegranskat)abstract
- A pair of tetranuclear iron complexes consisting of two Fe-2(Cl(2)bdt)(CO)(5) subunits (Cl(2)bdt = 3,6-dicholorobenzene-1,2-dithiolate) bridged by different cyclic 1,5-diaza-3,7-diphosphacyclooctane (P2N2) ligands were prepared and structurally characterized. In the solid state, the P2N2 ligands adopt a boat conformation, which results in rather short distances between the two Fe-2(Cl(2)bdt)(CO)(5) clusters that promotes electronic communication across the diphosphine ligand.
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| 10. |
- Leandri, Valentina, et al.
(författare)
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Rapid Microwave-Assisted Self-Assembly of a Carboxylic-Acid-Terminated Dye on a TiO2 Photoanode
- 2018
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 1:1, s. 202-210
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly of carboxylic-acid-functionalized dyes on mesoporous, anatase TiO2 is at the heart of dye-sensitized solar cells (DSSCs). However, the process often requires 6-20 h of electrode immersion at room temperature in the dye-bath solutions. Here, we introduce a new, rapid microwave-assisted sensitization technique (MINAS), which significantly accelerates the sensitization process and yields high-quality, self-assembled films of an organic dye within 5 min. Targeted experiments show that the effects of the microwave radiation cannot be explained purely on the basis of the thermal component. The interaction of the microwave radiation with the conductive fluorine-doped tin oxide (FTO) electrical contact is a key aspect to consider and a unique feature of MWAS that is the likely cause for producing rapid self-assembly of the dye on the surface.
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