Prof. Dr. Oliver Wenger Department of Chemistry Profiles & Affiliations OverviewResearch Publications Projects & Collaborations Projects & Collaborations OverviewResearch Publications Projects & Collaborations Profiles & Affiliations Projects & Collaborations 15 foundShow per page10 10 20 50 A dual femtosecond laser system for ultra-broadband electronic and chiral spectroscopy from the femto- to the millisecond time scale Research Project | 2 Project MembersImported from Grants Tool 4703663 Understanding and controlling elementary reaction steps in photocatalytic mechanisms Research Project | 1 Project MembersImported from Grants Tool 4702601 Development and Application of Photoactive Earth-Abundant Metal Complexes Functionalized with Organic Chromophores Research Project | 1 Project MembersImported from Grants Tool 4701916 Light-Driven Charge Accumulation based on Earth-Abundant High-Potential Photosensitizers Research Project | 1 Project MembersLichtinduzierte Elektronentransfer-Reaktionen sind chemische Elementarschritte, die in der biologischen Photosynthese eine zentrale Rolle spielen. Ein grundlegendes Verständnis dieser Elementarschritte ist daher für die Umwandlung von Sonnenergie in chemisch gespeicherte Energie in künstlichen Photosynthese-Systemen von Interesse. Chemische Modellverbindungen, in denen ein Elektronen-Donor, eine lichtabsorbierende Einheit (der sogenannte Photosensibilisator) und ein Elektronen-Akzeptor kovalent miteinander verbunden sind, eignen sich besonders gut für grundlegende Untersuchungen, weil in solchen Triaden-Verbindungen die Elektronentransfer-Prozesse direkt beobachtbar sind. Bisherige Untersuchungen an Triaden-Verbindungen fokussierten vor allem auf die lichtinduzierte Übertragung von einzelnen Elektronen. In der biologischen Photosynthese werden jedoch pro Reaktionsumsatz meist mehrere Elektronen benötigt und daher hat die Natur Wege gefunden, mehrere Elektronen zu akkumulieren. In Triaden-Verbindungen ist dies bislang erst selten gelungen. In diesem Forschungsvorhaben sollen daher die Grundlagen der lichtgetriebenen Elektronen-Akkumulation in Triaden-Verbindungen erforscht werden. Frühere Studien an Triaden-Verbindungen verwendeten ausserdem sehr oft Photosensibilisatoren, die aus Edelmetallen bestehen. In diesem Projekt geht es auch darum, auf kostengünstigeren Metallen aufgebaute Triaden-Verbindungen zu untersuchen. Dies scheint aus Gründen der Nachhaltigkeit wünschenswert, und andererseits können von neuartigen Photosensibilisatoren besonders günstige Elektronentransfer-Eigenschaften erwartet werden. Photoactive complexes based on Earth-abundant transition metals Research Project | 1 Project MembersPhotoactive metal complexes are typically based on precious elements such as ruthenium, iridium, platinum or gold. Their continued use in applications such as lighting, sensing, dyes for solar cells, chromophores in artificial photosynthesis, sensitizers for photodynamic therapy and catalysts for synthetic organic photochemistry is neither sustainable nor economic. Modern coordination chemistry should therefore address the following question: Can we develop design principles for photoactive complexes based on Earth-abundant metals, which are as reliable as for their precious metal congeners, and can we furthermore establish conceptually new photophysics and photochemistry with Earth-abundant metal complexes? This proposal outlines how these challenges will be tackled by a make-and-measure research strategy, in which synthetic coordination chemistry will be combined with laser spectroscopy and photochemical studies. The overall project is divided into five mutually independent yet closely related subprojects, aiming to develop fundamentally new photoactive coordination compounds based on titanium, manganese, cobalt, nickel, molybdenum and tungsten. A team of experienced coordination chemists, spectroscopists and photochemists will address the following specific challenges: (1) Establish the design principles of new types of luminophores, in which the charge transfer direction after optical excitation is reversed compared to traditionally explored precious metal complexes. The resulting ligand-to-metal charge transfer (LMCT) excited states are comparatively little explored but hold great promise for brightly emissive new compounds, in which undesired nonradiative excited-state relaxation processes can ideally be suppressed to a large extent. (2) Obtain base metal complexes that are able to consecutively absorb two photons for photo-ionization and formation of solvated electrons in catalytic fashion. Solvated electrons are extremely strong reducing agents and would be applicable to a wide range of photoreactions. So far only complexes made from precious metals have been amenable to such photo-reactivity, and only in water but not in organic solvents. (3) Explore the possibility of achieving photodriven multi-electron transfer in dinuclear metal complexes, rather than the traditional single electron transfer behavior known from mononuclear complexes. Until now, most photocatalysts made from Earth-abundant metals were mononuclear, and they were only able to engage in the transfer of single electrons. Light-driven multi-electron transfer is of key importance for solar energy conversion. (4) Establish long-lived excited states in N 2 -containing metal complexes to understand the operating principles of photochemical activation of nitrogen. Although light-induced splitting of N 2 has been achieved in some selected cases using molecular catalysts, the basic principles of photochemical nitrogen activation remain elusive, and the excited-state behavior of N 2 -bridged dinuclear metal complexes deserves special attention. (5) Establish photoinduced hydrogen atom transfer as a reactivity mode of electronically excited metal complexes. Typically, excited metal complexes undergo photoinduced electron transfer, whereas hydrogen atom transfer is very rare. Photoinduced hydrogen atom transfer would give access to a much wider scope of photochemical reactions than electron transfer alone, and it would be particularly attractive to achieve this with complexes made from Earth-abundant metals. The main outcome of the overall proposed research program is a new class of coordination compounds based on cheap and abundant metals featuring photoactive excited states with a more diverse reactivity scope than well-known precious metal-based compounds. In other words, on top of making the important step from precious to abundant metals, we aim at the development of fundamentally new photophysics and photochemistry, going conceptually far beyond the current state-of-the-art. This basic research will have important implications for solar energy conversion, lighting, light harvesting, and synthetic photochemistry. Metal cooperativity for visible-light driven CO2 reduction with new photosensitizers and catalysts Research Project | 1 Project MembersThe catalytic reduction of carbon dioxide (CO2) represents a highly active and challenging research field. Especially the photocatalytic recycling of CO2 and its utilization as a carbon feedstock could show severe impact on the global carbon balance as it allows to lower greenhouse gas emissions analog to natural photosynthesis pathways. Towards that end, chemistry plays a key role in developing such technologies by addressing the fundamental scientific challenges. Herein, pre-eminent catalyst development is of paramount importance and both homogenous and heterogeneous approaches are widely pursued. Due to the numerous spectroscopic techniques available and ease of synthetic alterations, studies on molecular transition metal complexes are vital for obtaining mechanistic insight on structurally very well-defined systems and are thus highly attractive to develop fundamental strategies for selective CO2 reduction processes. This approach requires the know-how of synthetic coordination chemists, photochemists, electrochemists and spectroscopists and will herein be attempted by joint efforts of the Wenger, Apfel and Robert groups. Inspired by Nature that enables selective activation of CO2 utilizing enzymatic bi-metallic active sites with a facilitated and selective multi-electron/multi-proton reduction through metal cooperativity, synthetic bi-metallic complexes will be rationally developed employing only earth-abundant metals. Furthermore, by tuning and controlling the metal cooperativity by targeted design of ligand backbone structures, we will aim at a selective synthesis of methanol, methane or short-chain hydrocarbons from CO2 in visible-light driven processes. To enable a light-driven CO2 reduction, these novel catalytic systems, however, likewise require novel suitable and potent photosensitizers. Thus, photosensitizers made from earth abundant transition metals will be synthesized and investigated for their photophysical properties. Consequently, the photosensitizers and catalysts will be synchronized in an iterative process between all groups. These findings will have far-reaching implications for photochemistry in general, as well as for CO2 reduction and activation in particular. Branco Weiss Fellowship for Murielle Delley: Electric-Field Assisted Catalysis by Abundant Inorganic Materials Through Interfacial Fundamentals Research Project | 3 Project MembersFor a sustainable future we need energy- and resource-efficient catalytic processes that can be controlled externally and use catalysts made of earth-abundant elements. Binary inorganic materials, such as transition metal phosphides and chalcogenides, have shown great promise to replace noble metal catalysts in some areas, but catalysis has not been broadly explored. The goal is to develop customizable catalysis by abundant inorganic materials for complex chemistry and added-value chemical products through a fundamental understanding of their interfacial chemistry. Electric fields could provide an external control on catalysis that is complementary to the more common temperature and pressure controls used in chemical industry. Electrostatic effects, such as electric fields are thought to be a major contributor to enzymatic catalysis, but have not been broadly explored in chemical synthesis. Herein, we will probe electric fields as external controls on catalysis of reductive and oxidative transformations by abundant materials using electrochemical methods and in-situ surface-enhanced infrared absorption spectroscopy. These studies will be supported by elucidation of the structure, thermochemistry, and elementary reactivity of the operative surfaces and the fine-tuning of their catalytic properties by chemical tailoring. Together, these strategies could open up great opportunities for the technological application of binary materials in sustainable chemical processes and for chemical synthesis. Besseres Verständnis bekannter und Auffinden neuer lichtinduzierter Mechanismen durch quantitative Ein- und Zweipulslaserblitzlichtphotolyse Research Project | 2 Project MembersN/A NCCR Molecular Systems Engineering - phase 2 Research Project | 30 Project MembersMolecular Systems Engineering is a National Centre of Competence in Research (NCCR) funded by the Swiss National Science Foundation (SNSF), and headed by the University of Basel and the ETH Zurich. This NCCR combines expertise from chemistry, biology, physics, bioinformatics, and engineering. The overreaching aim is to develop tools and devices to monitor and manipulate off-equilibrium (bio)chemical systems. These may find applications in the synthesis of high added-value products, as innovative diagnostic tools and for the restoration of a desired cellular or organ function. Photoactive Metal Complexes from Earth-Abundant Elements and Multi-Electron Photochemistry in Donor-Acceptor Compounds Research Project | 1 Project MembersMany of the most widely used photoactive complexes known to date are made from precious elements such as Ru, Ir, Pt or Au. Their replacement by more earth-abundant metals is of long-standing interest, and the first half of this proposed research project aims to explore the possibility of obtaining fundamentally new luminescent and photoredox-active complexes with long-lived excited-states. The plan is to synthesize and investigate a broad range of metal complexes made from earth-abundant metals in various oxidation states that until now have received either extremely limited or no attention at all in photophysical and photochemical contexts. Specifically, it is planned to explore: (i) homoleptic d6 MLCT luminophores and photoredox catalysts made from Cr(0), Mn(I), or Mo(0) with novel chelating isocyanide ligands, (ii) heteroleptic d10 MLCT emitters made from Ni(0) and a combination of chelating diphosphine and diisocyanide ligands, (iii) d-d emitters based on six-coordinate V(II) or Mn(IV) (d3) complexes, (iv) d0 LMCT luminophores based on Ti(IV) or Zr(IV) with chelating ligands made from pyrrolic and phenolic binding units.While the focus of this project is on obtaining fundamental insight into the basic photophysics and photochemistry of these new metal complexes, the development of such compounds made from earth-abundant elements is of significant interest in the contexts of lighting devices, solar cells, sensors, photoredox catalysis in organic chemistry, or for sensitization of reactions leading to the conversion of (solar) light into chemically stored energy, i. e., for so-called solar fuels.The second half of this proposed project aims at gaining fundamental insight into multi-photon, multi-electron transfer reactions going conceptually far beyond traditional work on photoinduced single electron transfer in donor-acceptor compounds. Artificial photosynthesis will have to rely on multi-electron conversions such as water splitting and CO2 reduction, but currently many studies use sacrificial redox reagents to perform such reactions under irradiation with visible light. This approach will not permit sustainable light-to-chemical energy conversion, and therefore it is highly desirable to explore the basics of multi-photon, multi-electron transfer reactions, as well as the light-driven accumulation of multiple redox equivalents without sacrificial reagents. Toward this end, a series of very carefully designed donor-acceptor compounds will be synthesized and investigated by various photophysical methods. Electrochemical potential inversion, proton-coupled electron transfer (PCET), and redox relays will play an important role in the various sub-projects of this research endeavor. 12 12 OverviewResearch Publications Projects & Collaborations
Projects & Collaborations 15 foundShow per page10 10 20 50 A dual femtosecond laser system for ultra-broadband electronic and chiral spectroscopy from the femto- to the millisecond time scale Research Project | 2 Project MembersImported from Grants Tool 4703663 Understanding and controlling elementary reaction steps in photocatalytic mechanisms Research Project | 1 Project MembersImported from Grants Tool 4702601 Development and Application of Photoactive Earth-Abundant Metal Complexes Functionalized with Organic Chromophores Research Project | 1 Project MembersImported from Grants Tool 4701916 Light-Driven Charge Accumulation based on Earth-Abundant High-Potential Photosensitizers Research Project | 1 Project MembersLichtinduzierte Elektronentransfer-Reaktionen sind chemische Elementarschritte, die in der biologischen Photosynthese eine zentrale Rolle spielen. Ein grundlegendes Verständnis dieser Elementarschritte ist daher für die Umwandlung von Sonnenergie in chemisch gespeicherte Energie in künstlichen Photosynthese-Systemen von Interesse. Chemische Modellverbindungen, in denen ein Elektronen-Donor, eine lichtabsorbierende Einheit (der sogenannte Photosensibilisator) und ein Elektronen-Akzeptor kovalent miteinander verbunden sind, eignen sich besonders gut für grundlegende Untersuchungen, weil in solchen Triaden-Verbindungen die Elektronentransfer-Prozesse direkt beobachtbar sind. Bisherige Untersuchungen an Triaden-Verbindungen fokussierten vor allem auf die lichtinduzierte Übertragung von einzelnen Elektronen. In der biologischen Photosynthese werden jedoch pro Reaktionsumsatz meist mehrere Elektronen benötigt und daher hat die Natur Wege gefunden, mehrere Elektronen zu akkumulieren. In Triaden-Verbindungen ist dies bislang erst selten gelungen. In diesem Forschungsvorhaben sollen daher die Grundlagen der lichtgetriebenen Elektronen-Akkumulation in Triaden-Verbindungen erforscht werden. Frühere Studien an Triaden-Verbindungen verwendeten ausserdem sehr oft Photosensibilisatoren, die aus Edelmetallen bestehen. In diesem Projekt geht es auch darum, auf kostengünstigeren Metallen aufgebaute Triaden-Verbindungen zu untersuchen. Dies scheint aus Gründen der Nachhaltigkeit wünschenswert, und andererseits können von neuartigen Photosensibilisatoren besonders günstige Elektronentransfer-Eigenschaften erwartet werden. Photoactive complexes based on Earth-abundant transition metals Research Project | 1 Project MembersPhotoactive metal complexes are typically based on precious elements such as ruthenium, iridium, platinum or gold. Their continued use in applications such as lighting, sensing, dyes for solar cells, chromophores in artificial photosynthesis, sensitizers for photodynamic therapy and catalysts for synthetic organic photochemistry is neither sustainable nor economic. Modern coordination chemistry should therefore address the following question: Can we develop design principles for photoactive complexes based on Earth-abundant metals, which are as reliable as for their precious metal congeners, and can we furthermore establish conceptually new photophysics and photochemistry with Earth-abundant metal complexes? This proposal outlines how these challenges will be tackled by a make-and-measure research strategy, in which synthetic coordination chemistry will be combined with laser spectroscopy and photochemical studies. The overall project is divided into five mutually independent yet closely related subprojects, aiming to develop fundamentally new photoactive coordination compounds based on titanium, manganese, cobalt, nickel, molybdenum and tungsten. A team of experienced coordination chemists, spectroscopists and photochemists will address the following specific challenges: (1) Establish the design principles of new types of luminophores, in which the charge transfer direction after optical excitation is reversed compared to traditionally explored precious metal complexes. The resulting ligand-to-metal charge transfer (LMCT) excited states are comparatively little explored but hold great promise for brightly emissive new compounds, in which undesired nonradiative excited-state relaxation processes can ideally be suppressed to a large extent. (2) Obtain base metal complexes that are able to consecutively absorb two photons for photo-ionization and formation of solvated electrons in catalytic fashion. Solvated electrons are extremely strong reducing agents and would be applicable to a wide range of photoreactions. So far only complexes made from precious metals have been amenable to such photo-reactivity, and only in water but not in organic solvents. (3) Explore the possibility of achieving photodriven multi-electron transfer in dinuclear metal complexes, rather than the traditional single electron transfer behavior known from mononuclear complexes. Until now, most photocatalysts made from Earth-abundant metals were mononuclear, and they were only able to engage in the transfer of single electrons. Light-driven multi-electron transfer is of key importance for solar energy conversion. (4) Establish long-lived excited states in N 2 -containing metal complexes to understand the operating principles of photochemical activation of nitrogen. Although light-induced splitting of N 2 has been achieved in some selected cases using molecular catalysts, the basic principles of photochemical nitrogen activation remain elusive, and the excited-state behavior of N 2 -bridged dinuclear metal complexes deserves special attention. (5) Establish photoinduced hydrogen atom transfer as a reactivity mode of electronically excited metal complexes. Typically, excited metal complexes undergo photoinduced electron transfer, whereas hydrogen atom transfer is very rare. Photoinduced hydrogen atom transfer would give access to a much wider scope of photochemical reactions than electron transfer alone, and it would be particularly attractive to achieve this with complexes made from Earth-abundant metals. The main outcome of the overall proposed research program is a new class of coordination compounds based on cheap and abundant metals featuring photoactive excited states with a more diverse reactivity scope than well-known precious metal-based compounds. In other words, on top of making the important step from precious to abundant metals, we aim at the development of fundamentally new photophysics and photochemistry, going conceptually far beyond the current state-of-the-art. This basic research will have important implications for solar energy conversion, lighting, light harvesting, and synthetic photochemistry. Metal cooperativity for visible-light driven CO2 reduction with new photosensitizers and catalysts Research Project | 1 Project MembersThe catalytic reduction of carbon dioxide (CO2) represents a highly active and challenging research field. Especially the photocatalytic recycling of CO2 and its utilization as a carbon feedstock could show severe impact on the global carbon balance as it allows to lower greenhouse gas emissions analog to natural photosynthesis pathways. Towards that end, chemistry plays a key role in developing such technologies by addressing the fundamental scientific challenges. Herein, pre-eminent catalyst development is of paramount importance and both homogenous and heterogeneous approaches are widely pursued. Due to the numerous spectroscopic techniques available and ease of synthetic alterations, studies on molecular transition metal complexes are vital for obtaining mechanistic insight on structurally very well-defined systems and are thus highly attractive to develop fundamental strategies for selective CO2 reduction processes. This approach requires the know-how of synthetic coordination chemists, photochemists, electrochemists and spectroscopists and will herein be attempted by joint efforts of the Wenger, Apfel and Robert groups. Inspired by Nature that enables selective activation of CO2 utilizing enzymatic bi-metallic active sites with a facilitated and selective multi-electron/multi-proton reduction through metal cooperativity, synthetic bi-metallic complexes will be rationally developed employing only earth-abundant metals. Furthermore, by tuning and controlling the metal cooperativity by targeted design of ligand backbone structures, we will aim at a selective synthesis of methanol, methane or short-chain hydrocarbons from CO2 in visible-light driven processes. To enable a light-driven CO2 reduction, these novel catalytic systems, however, likewise require novel suitable and potent photosensitizers. Thus, photosensitizers made from earth abundant transition metals will be synthesized and investigated for their photophysical properties. Consequently, the photosensitizers and catalysts will be synchronized in an iterative process between all groups. These findings will have far-reaching implications for photochemistry in general, as well as for CO2 reduction and activation in particular. Branco Weiss Fellowship for Murielle Delley: Electric-Field Assisted Catalysis by Abundant Inorganic Materials Through Interfacial Fundamentals Research Project | 3 Project MembersFor a sustainable future we need energy- and resource-efficient catalytic processes that can be controlled externally and use catalysts made of earth-abundant elements. Binary inorganic materials, such as transition metal phosphides and chalcogenides, have shown great promise to replace noble metal catalysts in some areas, but catalysis has not been broadly explored. The goal is to develop customizable catalysis by abundant inorganic materials for complex chemistry and added-value chemical products through a fundamental understanding of their interfacial chemistry. Electric fields could provide an external control on catalysis that is complementary to the more common temperature and pressure controls used in chemical industry. Electrostatic effects, such as electric fields are thought to be a major contributor to enzymatic catalysis, but have not been broadly explored in chemical synthesis. Herein, we will probe electric fields as external controls on catalysis of reductive and oxidative transformations by abundant materials using electrochemical methods and in-situ surface-enhanced infrared absorption spectroscopy. These studies will be supported by elucidation of the structure, thermochemistry, and elementary reactivity of the operative surfaces and the fine-tuning of their catalytic properties by chemical tailoring. Together, these strategies could open up great opportunities for the technological application of binary materials in sustainable chemical processes and for chemical synthesis. Besseres Verständnis bekannter und Auffinden neuer lichtinduzierter Mechanismen durch quantitative Ein- und Zweipulslaserblitzlichtphotolyse Research Project | 2 Project MembersN/A NCCR Molecular Systems Engineering - phase 2 Research Project | 30 Project MembersMolecular Systems Engineering is a National Centre of Competence in Research (NCCR) funded by the Swiss National Science Foundation (SNSF), and headed by the University of Basel and the ETH Zurich. This NCCR combines expertise from chemistry, biology, physics, bioinformatics, and engineering. The overreaching aim is to develop tools and devices to monitor and manipulate off-equilibrium (bio)chemical systems. These may find applications in the synthesis of high added-value products, as innovative diagnostic tools and for the restoration of a desired cellular or organ function. Photoactive Metal Complexes from Earth-Abundant Elements and Multi-Electron Photochemistry in Donor-Acceptor Compounds Research Project | 1 Project MembersMany of the most widely used photoactive complexes known to date are made from precious elements such as Ru, Ir, Pt or Au. Their replacement by more earth-abundant metals is of long-standing interest, and the first half of this proposed research project aims to explore the possibility of obtaining fundamentally new luminescent and photoredox-active complexes with long-lived excited-states. The plan is to synthesize and investigate a broad range of metal complexes made from earth-abundant metals in various oxidation states that until now have received either extremely limited or no attention at all in photophysical and photochemical contexts. Specifically, it is planned to explore: (i) homoleptic d6 MLCT luminophores and photoredox catalysts made from Cr(0), Mn(I), or Mo(0) with novel chelating isocyanide ligands, (ii) heteroleptic d10 MLCT emitters made from Ni(0) and a combination of chelating diphosphine and diisocyanide ligands, (iii) d-d emitters based on six-coordinate V(II) or Mn(IV) (d3) complexes, (iv) d0 LMCT luminophores based on Ti(IV) or Zr(IV) with chelating ligands made from pyrrolic and phenolic binding units.While the focus of this project is on obtaining fundamental insight into the basic photophysics and photochemistry of these new metal complexes, the development of such compounds made from earth-abundant elements is of significant interest in the contexts of lighting devices, solar cells, sensors, photoredox catalysis in organic chemistry, or for sensitization of reactions leading to the conversion of (solar) light into chemically stored energy, i. e., for so-called solar fuels.The second half of this proposed project aims at gaining fundamental insight into multi-photon, multi-electron transfer reactions going conceptually far beyond traditional work on photoinduced single electron transfer in donor-acceptor compounds. Artificial photosynthesis will have to rely on multi-electron conversions such as water splitting and CO2 reduction, but currently many studies use sacrificial redox reagents to perform such reactions under irradiation with visible light. This approach will not permit sustainable light-to-chemical energy conversion, and therefore it is highly desirable to explore the basics of multi-photon, multi-electron transfer reactions, as well as the light-driven accumulation of multiple redox equivalents without sacrificial reagents. Toward this end, a series of very carefully designed donor-acceptor compounds will be synthesized and investigated by various photophysical methods. Electrochemical potential inversion, proton-coupled electron transfer (PCET), and redox relays will play an important role in the various sub-projects of this research endeavor. 12 12
A dual femtosecond laser system for ultra-broadband electronic and chiral spectroscopy from the femto- to the millisecond time scale Research Project | 2 Project MembersImported from Grants Tool 4703663
Understanding and controlling elementary reaction steps in photocatalytic mechanisms Research Project | 1 Project MembersImported from Grants Tool 4702601
Development and Application of Photoactive Earth-Abundant Metal Complexes Functionalized with Organic Chromophores Research Project | 1 Project MembersImported from Grants Tool 4701916
Light-Driven Charge Accumulation based on Earth-Abundant High-Potential Photosensitizers Research Project | 1 Project MembersLichtinduzierte Elektronentransfer-Reaktionen sind chemische Elementarschritte, die in der biologischen Photosynthese eine zentrale Rolle spielen. Ein grundlegendes Verständnis dieser Elementarschritte ist daher für die Umwandlung von Sonnenergie in chemisch gespeicherte Energie in künstlichen Photosynthese-Systemen von Interesse. Chemische Modellverbindungen, in denen ein Elektronen-Donor, eine lichtabsorbierende Einheit (der sogenannte Photosensibilisator) und ein Elektronen-Akzeptor kovalent miteinander verbunden sind, eignen sich besonders gut für grundlegende Untersuchungen, weil in solchen Triaden-Verbindungen die Elektronentransfer-Prozesse direkt beobachtbar sind. Bisherige Untersuchungen an Triaden-Verbindungen fokussierten vor allem auf die lichtinduzierte Übertragung von einzelnen Elektronen. In der biologischen Photosynthese werden jedoch pro Reaktionsumsatz meist mehrere Elektronen benötigt und daher hat die Natur Wege gefunden, mehrere Elektronen zu akkumulieren. In Triaden-Verbindungen ist dies bislang erst selten gelungen. In diesem Forschungsvorhaben sollen daher die Grundlagen der lichtgetriebenen Elektronen-Akkumulation in Triaden-Verbindungen erforscht werden. Frühere Studien an Triaden-Verbindungen verwendeten ausserdem sehr oft Photosensibilisatoren, die aus Edelmetallen bestehen. In diesem Projekt geht es auch darum, auf kostengünstigeren Metallen aufgebaute Triaden-Verbindungen zu untersuchen. Dies scheint aus Gründen der Nachhaltigkeit wünschenswert, und andererseits können von neuartigen Photosensibilisatoren besonders günstige Elektronentransfer-Eigenschaften erwartet werden.
Photoactive complexes based on Earth-abundant transition metals Research Project | 1 Project MembersPhotoactive metal complexes are typically based on precious elements such as ruthenium, iridium, platinum or gold. Their continued use in applications such as lighting, sensing, dyes for solar cells, chromophores in artificial photosynthesis, sensitizers for photodynamic therapy and catalysts for synthetic organic photochemistry is neither sustainable nor economic. Modern coordination chemistry should therefore address the following question: Can we develop design principles for photoactive complexes based on Earth-abundant metals, which are as reliable as for their precious metal congeners, and can we furthermore establish conceptually new photophysics and photochemistry with Earth-abundant metal complexes? This proposal outlines how these challenges will be tackled by a make-and-measure research strategy, in which synthetic coordination chemistry will be combined with laser spectroscopy and photochemical studies. The overall project is divided into five mutually independent yet closely related subprojects, aiming to develop fundamentally new photoactive coordination compounds based on titanium, manganese, cobalt, nickel, molybdenum and tungsten. A team of experienced coordination chemists, spectroscopists and photochemists will address the following specific challenges: (1) Establish the design principles of new types of luminophores, in which the charge transfer direction after optical excitation is reversed compared to traditionally explored precious metal complexes. The resulting ligand-to-metal charge transfer (LMCT) excited states are comparatively little explored but hold great promise for brightly emissive new compounds, in which undesired nonradiative excited-state relaxation processes can ideally be suppressed to a large extent. (2) Obtain base metal complexes that are able to consecutively absorb two photons for photo-ionization and formation of solvated electrons in catalytic fashion. Solvated electrons are extremely strong reducing agents and would be applicable to a wide range of photoreactions. So far only complexes made from precious metals have been amenable to such photo-reactivity, and only in water but not in organic solvents. (3) Explore the possibility of achieving photodriven multi-electron transfer in dinuclear metal complexes, rather than the traditional single electron transfer behavior known from mononuclear complexes. Until now, most photocatalysts made from Earth-abundant metals were mononuclear, and they were only able to engage in the transfer of single electrons. Light-driven multi-electron transfer is of key importance for solar energy conversion. (4) Establish long-lived excited states in N 2 -containing metal complexes to understand the operating principles of photochemical activation of nitrogen. Although light-induced splitting of N 2 has been achieved in some selected cases using molecular catalysts, the basic principles of photochemical nitrogen activation remain elusive, and the excited-state behavior of N 2 -bridged dinuclear metal complexes deserves special attention. (5) Establish photoinduced hydrogen atom transfer as a reactivity mode of electronically excited metal complexes. Typically, excited metal complexes undergo photoinduced electron transfer, whereas hydrogen atom transfer is very rare. Photoinduced hydrogen atom transfer would give access to a much wider scope of photochemical reactions than electron transfer alone, and it would be particularly attractive to achieve this with complexes made from Earth-abundant metals. The main outcome of the overall proposed research program is a new class of coordination compounds based on cheap and abundant metals featuring photoactive excited states with a more diverse reactivity scope than well-known precious metal-based compounds. In other words, on top of making the important step from precious to abundant metals, we aim at the development of fundamentally new photophysics and photochemistry, going conceptually far beyond the current state-of-the-art. This basic research will have important implications for solar energy conversion, lighting, light harvesting, and synthetic photochemistry.
Metal cooperativity for visible-light driven CO2 reduction with new photosensitizers and catalysts Research Project | 1 Project MembersThe catalytic reduction of carbon dioxide (CO2) represents a highly active and challenging research field. Especially the photocatalytic recycling of CO2 and its utilization as a carbon feedstock could show severe impact on the global carbon balance as it allows to lower greenhouse gas emissions analog to natural photosynthesis pathways. Towards that end, chemistry plays a key role in developing such technologies by addressing the fundamental scientific challenges. Herein, pre-eminent catalyst development is of paramount importance and both homogenous and heterogeneous approaches are widely pursued. Due to the numerous spectroscopic techniques available and ease of synthetic alterations, studies on molecular transition metal complexes are vital for obtaining mechanistic insight on structurally very well-defined systems and are thus highly attractive to develop fundamental strategies for selective CO2 reduction processes. This approach requires the know-how of synthetic coordination chemists, photochemists, electrochemists and spectroscopists and will herein be attempted by joint efforts of the Wenger, Apfel and Robert groups. Inspired by Nature that enables selective activation of CO2 utilizing enzymatic bi-metallic active sites with a facilitated and selective multi-electron/multi-proton reduction through metal cooperativity, synthetic bi-metallic complexes will be rationally developed employing only earth-abundant metals. Furthermore, by tuning and controlling the metal cooperativity by targeted design of ligand backbone structures, we will aim at a selective synthesis of methanol, methane or short-chain hydrocarbons from CO2 in visible-light driven processes. To enable a light-driven CO2 reduction, these novel catalytic systems, however, likewise require novel suitable and potent photosensitizers. Thus, photosensitizers made from earth abundant transition metals will be synthesized and investigated for their photophysical properties. Consequently, the photosensitizers and catalysts will be synchronized in an iterative process between all groups. These findings will have far-reaching implications for photochemistry in general, as well as for CO2 reduction and activation in particular.
Branco Weiss Fellowship for Murielle Delley: Electric-Field Assisted Catalysis by Abundant Inorganic Materials Through Interfacial Fundamentals Research Project | 3 Project MembersFor a sustainable future we need energy- and resource-efficient catalytic processes that can be controlled externally and use catalysts made of earth-abundant elements. Binary inorganic materials, such as transition metal phosphides and chalcogenides, have shown great promise to replace noble metal catalysts in some areas, but catalysis has not been broadly explored. The goal is to develop customizable catalysis by abundant inorganic materials for complex chemistry and added-value chemical products through a fundamental understanding of their interfacial chemistry. Electric fields could provide an external control on catalysis that is complementary to the more common temperature and pressure controls used in chemical industry. Electrostatic effects, such as electric fields are thought to be a major contributor to enzymatic catalysis, but have not been broadly explored in chemical synthesis. Herein, we will probe electric fields as external controls on catalysis of reductive and oxidative transformations by abundant materials using electrochemical methods and in-situ surface-enhanced infrared absorption spectroscopy. These studies will be supported by elucidation of the structure, thermochemistry, and elementary reactivity of the operative surfaces and the fine-tuning of their catalytic properties by chemical tailoring. Together, these strategies could open up great opportunities for the technological application of binary materials in sustainable chemical processes and for chemical synthesis.
Besseres Verständnis bekannter und Auffinden neuer lichtinduzierter Mechanismen durch quantitative Ein- und Zweipulslaserblitzlichtphotolyse Research Project | 2 Project MembersN/A
NCCR Molecular Systems Engineering - phase 2 Research Project | 30 Project MembersMolecular Systems Engineering is a National Centre of Competence in Research (NCCR) funded by the Swiss National Science Foundation (SNSF), and headed by the University of Basel and the ETH Zurich. This NCCR combines expertise from chemistry, biology, physics, bioinformatics, and engineering. The overreaching aim is to develop tools and devices to monitor and manipulate off-equilibrium (bio)chemical systems. These may find applications in the synthesis of high added-value products, as innovative diagnostic tools and for the restoration of a desired cellular or organ function.
Photoactive Metal Complexes from Earth-Abundant Elements and Multi-Electron Photochemistry in Donor-Acceptor Compounds Research Project | 1 Project MembersMany of the most widely used photoactive complexes known to date are made from precious elements such as Ru, Ir, Pt or Au. Their replacement by more earth-abundant metals is of long-standing interest, and the first half of this proposed research project aims to explore the possibility of obtaining fundamentally new luminescent and photoredox-active complexes with long-lived excited-states. The plan is to synthesize and investigate a broad range of metal complexes made from earth-abundant metals in various oxidation states that until now have received either extremely limited or no attention at all in photophysical and photochemical contexts. Specifically, it is planned to explore: (i) homoleptic d6 MLCT luminophores and photoredox catalysts made from Cr(0), Mn(I), or Mo(0) with novel chelating isocyanide ligands, (ii) heteroleptic d10 MLCT emitters made from Ni(0) and a combination of chelating diphosphine and diisocyanide ligands, (iii) d-d emitters based on six-coordinate V(II) or Mn(IV) (d3) complexes, (iv) d0 LMCT luminophores based on Ti(IV) or Zr(IV) with chelating ligands made from pyrrolic and phenolic binding units.While the focus of this project is on obtaining fundamental insight into the basic photophysics and photochemistry of these new metal complexes, the development of such compounds made from earth-abundant elements is of significant interest in the contexts of lighting devices, solar cells, sensors, photoredox catalysis in organic chemistry, or for sensitization of reactions leading to the conversion of (solar) light into chemically stored energy, i. e., for so-called solar fuels.The second half of this proposed project aims at gaining fundamental insight into multi-photon, multi-electron transfer reactions going conceptually far beyond traditional work on photoinduced single electron transfer in donor-acceptor compounds. Artificial photosynthesis will have to rely on multi-electron conversions such as water splitting and CO2 reduction, but currently many studies use sacrificial redox reagents to perform such reactions under irradiation with visible light. This approach will not permit sustainable light-to-chemical energy conversion, and therefore it is highly desirable to explore the basics of multi-photon, multi-electron transfer reactions, as well as the light-driven accumulation of multiple redox equivalents without sacrificial reagents. Toward this end, a series of very carefully designed donor-acceptor compounds will be synthesized and investigated by various photophysical methods. Electrochemical potential inversion, proton-coupled electron transfer (PCET), and redox relays will play an important role in the various sub-projects of this research endeavor.
