Femtosecond Soft X-ray Spectroscopy of Solvated Transition-Metal Complexes: Deciphering the Interplay of Electronic and Structural Dynamics

We present the first implementation of femtosecond soft X-ray spectroscopy as an ultrafast direct probe of the excited-state valence orbitals in solution phase molecules. This method is applied to photoinduced spin crossover of [Fe(tren(py)(3))](2+), where the ultrafast spin state conversion of the metal ion, initiated by metal-to-ligand charge transfer excitation, is directly measured using the intrinsic spin state selectivity of the soft X-ray L-edge transitions. Our results provide important experimental data concerning the mechanism of ultrafast spin state conversion and subsequent electronic and structural dynamics, highlighting the potential of this technique to study ultrafast phenomena in the solution phase.