Charge transfer Raman, XES and (HR)XAS studies on Type Zero model complexes

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The aim of this proposal is to achieve an improved understanding of copper Type Zero compounds by a combined synthetic and advanced spectroscopy approach. It is targeted at the development of new biomimetic model complexes for Type Zero copper systems and the application of Raman and X-ray spectroscopic methods on these complexes in order to study their excited states. Such a multi-dimensional spectroscopic approach by X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), high energy resolution fluorescence detected XAS (HERFD-XAS), Raman spectroscopy and pump-probe measurements in combination with electrochemical experiments is unique for that purpose.It will allow to study the electronic and geometric structure of the individual species of the Cu(I)/Cu(II) redox pair as well as the kinetics of these two parameters in course of chemical, electrochemical and photoinduced redox processes.In the synthetic part of the project, model complexes for Type Zero proteins bearing N,N´ as well as N,O donor ligands will be prepared, i.e. guanidine bis(chelate) copper complexes and bis(pyrazolyl)phenolmethane copper phenolate complexes.The interconnection between synthesis and spectroscopy is mandatory due to following reasons: The ligand design is spectroscopy aided, i.e. the choice of ligand substitution is based on absorption and emission properties. On the other hand, the spectroscopic characterization of the prepared complexes will prove their usefulness as structural models. Finally the investigation of their electron transfer properties will determine their usefulness as functional models.The best models will finally be subjected to detailed spectroscopic investigations of their electronic and geometric structure, the ambivalent influence of these two structures on each other, and their dynamic evolution after photoexcitation and during electrochemical experiments. While conventional XAS and pump-probe XAS were already developed and established for the purpose of the research group, the experimental and theoretical foundations for K-edge XES and HERFD-XAS applied to Type Zero systems are one of the key spectroscopic developments of this project. This includes the development of an X-ray spectro-electrochemical cell for XES and HERFD-XAS as well as exploratory pump-probe experiments, which will be completed by the development of a spectro-electrochemical cell for simultaneous X-ray and Raman measurements.In combination with resonance Raman and L-edge XAS, this project will allow unique new insights into the working principle of Type Zero copper proteins. As ultimate goal, we target the development of an optically triggered fast electron transfer system based on the small molecule Type Zero analogues and to understand the concomitant structural distortions associated with the electronic charge transfer and its impact on the function of the system.