Light-driven photoredox catalysis is one functional example for which complex electron transfer chains are key to the overall function. For instance, proton reduction is a two-electron-two-proton process involving at least two light-driven electron transfers. Conventional spectroscopy to study electronically excited states, e.g. resonance Raman or ultrafast transient absorption spectroscopy, is only capable of capturing the first of the sequential electron transfer steps. Therefore, we develop complex spectroelectrochemical tools, combining cyclovoltammetry and chronoamperometry with resonance Raman, ultrafast transient absorption and time-resolved emission spectroscopy, to first generate molecular intermediates of electron transfer chains electrochemically and then study their excited-state properties spectroscopically.
We assemble molecularly functionalized photoelectrodes, i.e. ZnO and TiO2 based anodes and NiO based cathodes, and functionally characterize them in dye-sensitized solar cells and photoelectrochemcial cells. Finally, we spectroscopically access the photodriven elementary reactions, which underlie the overall function of the photoelectrodes, by time-resolved spectroscopy. Recently, within the CRC/TRR 234 CataLight we started to work on fully-organic photocathode materials, in which the function of the NiO is replaced by hole conducting polymers.
Local environments alter the optical properties and molecular responses to external stimuli, e.g. light absorption. Thus, we study the impact of increasingly complex environments on the excited-state dynamics of small molecules, which are used as light-activated drugs or fluorescence sensors in biology and medicine. To this end we either work on model environments, e.g. upon addition of well defined biopolymers or electrolytes, or develop spectroscopic setups to perform ultrafast time-resolution spectroscopy on cultivated cells.
Within the CRC/TRR 234 CataLight we study the molecular mechanisms of photodriven redox-catalysts for water splitting. The primary light-activated processes leading to intra- and intermolecular charge transfer are studied by femtosecond pump-probe spectroscopy, time-resolved luminescence spectroscopy and resonance Raman scattering. To characterize catalytically competent systems during catalysis we strive to develop ultrafast time-resolved in-situ and in-operando spectroscopy.
Recently we started work on spectroscopically accessing the electrode electrolyte interface, by designing specific fluorescence sensor molecules and vibrational sum-frequency generation. Our goal is to understand the local structure of adsorbates and solvent at the solid-electrolyte interface.