Photodynamics of transition metal complexes

We use Kα/Kβ X-ray Emission Spectroscopy (XES) to elucidate the role of the metal-centered excited states in the relaxation dynamics of transition metal coordination complexes. Initially we have focused on the light-induced spin crossover in Fe(II) compounds. The spin dynamics of these systems plays a central role for a potential application of these materials, both for light-driven data storage and in dye-sensitized solar cells. The spin crossover is critical: It controls the switching time, but also competes with charge injection.

Resonant Inelastic X-ray Scattering (RIXS) gives atom-specific information about the unoccupied and occupied frontier orbitals. With the development of intense soft X-ray sources with high repetition rate, i.e. Free-Electron-Lasers, this method becomes attractive for our time-resolved experiments.

In many photoreactions of transition metal coordination compounds the metal center plays a decisive role. Therefore it is of great interest to characterize the local electronic and binding structure at the metal center. For this, we use hard X-ray Absorption Near-Edge Structure (XANES) spectroscopy und Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. In addition, with femtosecond time-resolved Wide Angle X-ray Scattering (WAXS) we elucidate the global structure. This also includes site-specific interactions of the solute with the metal. We have used these methods to study the reaction mechanisms as well as to identify the photochemical transient states after the photoexcitation of Cu(I) complexes with photocatalytic relevance.