Visible Light-Driven Water Oxidation Catalyzed by Ruthenium Complexes

A shift in energy dependence from fossil fuels to sustainable and carbon-neutral alternatives is a daunting challenge that faces the human society. Light harvesting for the production of solar fuels has been extensively investigated as an attractive approach to clean and abundant energy. An essential component in solar energy conversion schemes is a catalyst for water oxidation. Ruthenium-based catalysts have received significant attention due to their ability to efficiently mediate the oxidation of water. In this context, the design of robust catalysts capable of driving water oxidation at low overpotential is a key challenge for realizing efficient visible light-driven water splitting. Herein, recent progress in the development within this field is presented with a focus on homogeneous ruthenium-based systems and surface-immobilized ruthenium assemblies for photo-induced oxidation of water

Feedback Control in Silicon Photonic MEMS

In this report, we study the implementation of a feedback control system to stabilizea MEMS device for applications in programmable photonic circuits. Specifically, the controller wasimplemented on an all-pass ring resonator, as it was the most suitable MEMS device to implementthe control system on.This study aims to show that it is possible to stabilize MEMS using a feedback loop, therebyreducing their sensitivity to temperature and noise. We present a solution that uses a programmablehardware platform to implement a PI controller and conduct measurements to demonstrate theefficacy of the proposed approach.We experimentally show that it is possible to stabilize the MEMS using the feedback controller,but our results suggest that the MEMS device needs to display a linear response to the control signal.We also suggest improvements to the lab set-up that could further improve our results and workaround the non-linearity problem.I denna rapport, studerar vi implementeringen av ett återkopplatreglersystem för att stabilisera en MEMS-enhet för tillämpningar inom programmerbara fotoniskakretsar. Specifikt, implementerades reglersystemet på en all-pass ringresonator då den var den mestlämplig MEMS-enhet att implementera reglersystemet på.Syftet med denna studie är att visa att det är möjligt att stabilisera MEMS med återkoppling ochdärigenom minska deras känslighet för temperatur och brus. Vi presenterar en lösning som använderen programmerbar hårdvaruplattform för att implementera en PI-regulator och göra mätningar föratt demonstrera funktionaliteten av den föreslagna lösningen.Vi visar experimentellt att det är möjligt att stabilisera MEMS med ett återkopplat reglersystem,men våra resultat tyder på att MEMS-enheterna behöver visa ett delvis linjärt svar tillkontrollsignalen. Dessutom föreslår vi förbättringar till labbuppsättningen som ytterligare kanoptimera våra resultat och jobba runt linearitets problemet.Kandidatexjobb i elektroteknik 2023, KTH, Stockhol

Efficient Synthesis of 2-Substituted Imidazoles by Palladium-Catalyzed Cross-Coupling with Benzylzinc Reagents

Substituted benzylzinc reagents have been used in novel cross-coupling reactions with 2-iodo imidazoles to form compounds containing both a phenol and an imidazole moiety. The ­intramolecular hydrogen-bonding properties of these compounds were subsequently studied

Mimicking photosystem II reactions in artificial photosynthesis: Ru(II)-polypyridine photosensitisers linked to tyrosine and manganese electron donors

The paper describes a project aiming at constructing functional mimics of the oxygen evolving complex in photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyrosine, have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photooxidised Ru(III) complex was demonstrated using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn(III,III)->tyrosine->Ru(III) was demonstrated, in analogy to the reaction on the donor side of photosystem II. Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reaction in photosystem II is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser was observed. Preliminary results suggest the possibility of photooxidising manganese dimers in several steps, which is an important step towards water oxidation

A biomimetic approach to artificial photosynthesis: Ru(II)-polypyridine photo-sensitisers linked to tyrosine and manganese electron donors

The paper describes recent advances towards the construction of functional mimics of the oxygen evolving complex in photosystem II (PSII) that are coupled to photoinduced charge separation. Some key principles of PSII and artificial systems for light-induced charge accumulation are discussed. Systems are described where biomimetic electron donors - manganese complexes and tyrosine - have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photo-oxidised Ru(III) complex has been studied using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn2(III,III)->tyrosine->Ru(III) has been demonstrated, in analogy to the reaction on the donor side of PSII. Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reactions in PSII is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser has been observed. Preliminary results suggest the possibility of photo-oxidising manganese dimers in several steps, which is an important advancement towards water oxidation

Artificial photosynthesis: towards functional mimics of photosystem II?

This paper describes the initial development of a project aiming at the construction of functional mimics of the oxygen-evolving complex of photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyrosine, have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photo-oxidised Ru(III) complex was demonstrated using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn->tyrosine->Ru(III) was demonstrated

Towards artificial photosynthesis: ruthenium-manganese chemistry for energy production

The synthesis and characterisation of supramolecular model systems mimicking the light reactions on the donor side of Photosystem II (PSII) in green plants have been reviewed. In these systems, manganese complexes and tyrosine are electron donors, modelling the manganese cluster and tyrosineZ in PSII. The donors have been covalently linked to a photosensitizer, a ruthenium(ii) tris-bipyridyl complex, that plays the role of the P680 chlorophylls in PSII. It has been demonstrated that, in the presence of an external electron acceptor in solution, the model systems can undergo an intermolecular electron transfer from the photoexcited state of RuII to an acceptor, followed by an intramolecular electron transfer from the coordinated Mn complexes or the tyrosine unit to the photogenerated RuIII. This leads to regeneration of the RuII and oxidation of the Mn complexes or generation of a tyrosine radical. The process closely mimics the primary reaction steps on the donor side of PSII