Transient-absorption spectroelectrochemistry for studying excited states in electrochemically generated molecular species in solution

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Electron transfer processes are ubiquitous in biology, chemistry and physics. Electron transfer processes present key elementary steps in e.g. photosynthesis and the respiratory chain. Furthermore, (photoinduced) electron transfer steps present the molecular-mechanistic basis for e.g. dye-sensitized solar cells and molecular photocatalysts. During a stepwise electron transfer, irrespective of natural or artificial systems being considered, intermediate reduced/oxidized species are formed, whose photophysics is largely unexploited. The absence of (ultrafast) spectroscopic information about these intermediates is in marked contrast to their functional importance within the electron transfer cascades. Filling this gap in understanding the photoinduced excited-state processes in molecular intermediates of multi-step electron transfer reactions in selected model systems is at the core of this proposal.The project aims at characterizing the photoinduced dynamics in electrochemically produced molecular species in solution by combining cyclovoltammetry and femtosecond time-resolved transient absorption spectroscopy. In doing so the photoinduced processes in exemplarily selected photocatalysts for proton reduction and electron donors for dye-sensitized solar cells in their electrochemically reduced and oxidized forms will be spectroscopically characterized. Hence, the work proposed here will establish a novel approach to study the interplay between structure, dynamics and function of molecular species within an experimental window, which has not been used in previous experiments. Thus, the proposed work will also yield new impulses for further investigations, which will go beyond studying the specific model systems, which are considered here.