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Photoactive complexes based on Earth-abundant transition metals

Research Project
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01.08.2022
 - 31.07.2026

Photoactive 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.

Funding

Photoactive complexes based on Earth-abundant transition metals

SNF Projekt (GrantsTool), 08.2022-07.2026 (48)
PI : Wenger, Oliver.

Members (1)

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Oliver Wenger

Principal Investigator