Anorganische Chemie (Wenger)Head of Research Unit Prof. Dr.Oliver WengerOverviewMembersPublicationsProjects & CollaborationsProjects & Collaborations OverviewMembersPublicationsProjects & Collaborations Projects & Collaborations 13 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. Development of Organic Photosensitizers for Visible-Light Driven Birch Reductions Research Project | 2 Project MembersNo Description available Besseres Verständnis bekannter und Auffinden neuer lichtinduzierter Mechanismen durch quantitative Ein- und Zweipulslaserblitzlichtphotolyse Research Project | 2 Project MembersN/A 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. Synthesis, Photophysics and Photochemistry of Uncommon Transition Metal Complexes Research Project | 6 Project Members2,2'-bipyridine and related alpha-diimine ligands form luminescent complexes with a variety of d6 and d8 metals, many of which are very well investigated. The phosphorous analog of 2,2'-bipyridine is called 2,2'-biphosphinine and has been known since 1991. Several transition metal complexes with 2,2'-biphosphinine have been synthesized but the photophysical and photochemical properties of these complexes have remained essentially unexplored. For well-selected complexes with bi- and tridentate phosphinine ligands there is good reason to expect similar (emissive) metal-to-ligand charge transfer (MLCT) excited states as for many alpha-diimine complexes of d6 and d8 metals. However, 2,2'-biphosphinine tends to stabilize metals in lower oxidation states than 2,2'-bipyridine, and some complexes of 2,2'-biphosphinine adopt a trigonal-prismatic geometry rather the octahedral coordination usually encountered in homoleptic 2,2'-bipyridine d6 metal complexes. In addition, 2,2'-biphosphinine is more redox non-innocent than 2,2'-bipyridine. One can therefore expect certain analogies but also some pronounced differences between the photophysics of 2,2'-biphosphinine and 2,2'-bipyridine complexes. The goal of the first part of this proposal (sub-project 1) is to synthesize new luminescent metal complexes with bi- or tridentante phosphinine ligands and to obtain a detailed fundamental understanding of their photophysical and photochemical properties. The work will not be limited to 2,2'-biphosphinine and its derivatives but will encompass bi- and tridentate chelating ligands including for example pyridylphosphinines and phenylphosphinines. This research has the potential to lead to new luminescent materials, photo- or electrocatalysts for CO2 reduction, photosensitizers for dye-sensitized solar cells, potent photooxidants for electron transfer studies in proteins, DNA intercalators, or chemical sensors for volatile organic compounds. The second part of the proposed research (sub-project 2) concentrates on novel bipyridine and terpyridine ligands which are expected to show catechol-like redox properties (Figure 2). The ultimate goal is to develop new transition metal complexes which can undergo multiple oxidations in a reversible fashion at relatively modest electrochemical potentials. Such complexes are of interest as catalysts for a variety of different multi-electron conversions including for example water oxidation or CO2 fixation. Common alpha-diimine complexes such as [Ru(2,2'-bipyridine)3]2+ exhibit simple one-electron redox chemistry, and they usually cannot undergo multi-electron reactions. The ligands in Figure 2 are expected to be highly redox-active, and when coordinated to metal complexes unusually rich multi-electron (photo)redox chemistry might result. Multiple oxidations of these complexes should be possible over a relatively small potential window due to the fact that the respective ligands can release protons upon oxidation, thereby avoiding the formation of highly charged species. Initial work will focus mostly on substitution-inert d6 metal complexes, but in the mid- to long-term more earth-abundant 3d metals will be investigated. 12 12 OverviewMembersPublicationsProjects & Collaborations
Projects & Collaborations 13 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. Development of Organic Photosensitizers for Visible-Light Driven Birch Reductions Research Project | 2 Project MembersNo Description available Besseres Verständnis bekannter und Auffinden neuer lichtinduzierter Mechanismen durch quantitative Ein- und Zweipulslaserblitzlichtphotolyse Research Project | 2 Project MembersN/A 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. Synthesis, Photophysics and Photochemistry of Uncommon Transition Metal Complexes Research Project | 6 Project Members2,2'-bipyridine and related alpha-diimine ligands form luminescent complexes with a variety of d6 and d8 metals, many of which are very well investigated. The phosphorous analog of 2,2'-bipyridine is called 2,2'-biphosphinine and has been known since 1991. Several transition metal complexes with 2,2'-biphosphinine have been synthesized but the photophysical and photochemical properties of these complexes have remained essentially unexplored. For well-selected complexes with bi- and tridentate phosphinine ligands there is good reason to expect similar (emissive) metal-to-ligand charge transfer (MLCT) excited states as for many alpha-diimine complexes of d6 and d8 metals. However, 2,2'-biphosphinine tends to stabilize metals in lower oxidation states than 2,2'-bipyridine, and some complexes of 2,2'-biphosphinine adopt a trigonal-prismatic geometry rather the octahedral coordination usually encountered in homoleptic 2,2'-bipyridine d6 metal complexes. In addition, 2,2'-biphosphinine is more redox non-innocent than 2,2'-bipyridine. One can therefore expect certain analogies but also some pronounced differences between the photophysics of 2,2'-biphosphinine and 2,2'-bipyridine complexes. The goal of the first part of this proposal (sub-project 1) is to synthesize new luminescent metal complexes with bi- or tridentante phosphinine ligands and to obtain a detailed fundamental understanding of their photophysical and photochemical properties. The work will not be limited to 2,2'-biphosphinine and its derivatives but will encompass bi- and tridentate chelating ligands including for example pyridylphosphinines and phenylphosphinines. This research has the potential to lead to new luminescent materials, photo- or electrocatalysts for CO2 reduction, photosensitizers for dye-sensitized solar cells, potent photooxidants for electron transfer studies in proteins, DNA intercalators, or chemical sensors for volatile organic compounds. The second part of the proposed research (sub-project 2) concentrates on novel bipyridine and terpyridine ligands which are expected to show catechol-like redox properties (Figure 2). The ultimate goal is to develop new transition metal complexes which can undergo multiple oxidations in a reversible fashion at relatively modest electrochemical potentials. Such complexes are of interest as catalysts for a variety of different multi-electron conversions including for example water oxidation or CO2 fixation. Common alpha-diimine complexes such as [Ru(2,2'-bipyridine)3]2+ exhibit simple one-electron redox chemistry, and they usually cannot undergo multi-electron reactions. The ligands in Figure 2 are expected to be highly redox-active, and when coordinated to metal complexes unusually rich multi-electron (photo)redox chemistry might result. Multiple oxidations of these complexes should be possible over a relatively small potential window due to the fact that the respective ligands can release protons upon oxidation, thereby avoiding the formation of highly charged species. Initial work will focus mostly on substitution-inert d6 metal complexes, but in the mid- to long-term more earth-abundant 3d metals will be investigated. 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.
Development of Organic Photosensitizers for Visible-Light Driven Birch Reductions Research Project | 2 Project MembersNo Description available
Besseres Verständnis bekannter und Auffinden neuer lichtinduzierter Mechanismen durch quantitative Ein- und Zweipulslaserblitzlichtphotolyse Research Project | 2 Project MembersN/A
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.
Synthesis, Photophysics and Photochemistry of Uncommon Transition Metal Complexes Research Project | 6 Project Members2,2'-bipyridine and related alpha-diimine ligands form luminescent complexes with a variety of d6 and d8 metals, many of which are very well investigated. The phosphorous analog of 2,2'-bipyridine is called 2,2'-biphosphinine and has been known since 1991. Several transition metal complexes with 2,2'-biphosphinine have been synthesized but the photophysical and photochemical properties of these complexes have remained essentially unexplored. For well-selected complexes with bi- and tridentate phosphinine ligands there is good reason to expect similar (emissive) metal-to-ligand charge transfer (MLCT) excited states as for many alpha-diimine complexes of d6 and d8 metals. However, 2,2'-biphosphinine tends to stabilize metals in lower oxidation states than 2,2'-bipyridine, and some complexes of 2,2'-biphosphinine adopt a trigonal-prismatic geometry rather the octahedral coordination usually encountered in homoleptic 2,2'-bipyridine d6 metal complexes. In addition, 2,2'-biphosphinine is more redox non-innocent than 2,2'-bipyridine. One can therefore expect certain analogies but also some pronounced differences between the photophysics of 2,2'-biphosphinine and 2,2'-bipyridine complexes. The goal of the first part of this proposal (sub-project 1) is to synthesize new luminescent metal complexes with bi- or tridentante phosphinine ligands and to obtain a detailed fundamental understanding of their photophysical and photochemical properties. The work will not be limited to 2,2'-biphosphinine and its derivatives but will encompass bi- and tridentate chelating ligands including for example pyridylphosphinines and phenylphosphinines. This research has the potential to lead to new luminescent materials, photo- or electrocatalysts for CO2 reduction, photosensitizers for dye-sensitized solar cells, potent photooxidants for electron transfer studies in proteins, DNA intercalators, or chemical sensors for volatile organic compounds. The second part of the proposed research (sub-project 2) concentrates on novel bipyridine and terpyridine ligands which are expected to show catechol-like redox properties (Figure 2). The ultimate goal is to develop new transition metal complexes which can undergo multiple oxidations in a reversible fashion at relatively modest electrochemical potentials. Such complexes are of interest as catalysts for a variety of different multi-electron conversions including for example water oxidation or CO2 fixation. Common alpha-diimine complexes such as [Ru(2,2'-bipyridine)3]2+ exhibit simple one-electron redox chemistry, and they usually cannot undergo multi-electron reactions. The ligands in Figure 2 are expected to be highly redox-active, and when coordinated to metal complexes unusually rich multi-electron (photo)redox chemistry might result. Multiple oxidations of these complexes should be possible over a relatively small potential window due to the fact that the respective ligands can release protons upon oxidation, thereby avoiding the formation of highly charged species. Initial work will focus mostly on substitution-inert d6 metal complexes, but in the mid- to long-term more earth-abundant 3d metals will be investigated.
