Ultrafast spin crossover in [FeII bpy 3]2 revealing two competing mechanisms by means of XUV photoemission spectroscopy

Photoinduced spin flip in FeII complexes is an ultrafast phenomenon that has the potential to become an alternative to conventional processing and magnetic storage of information. Following the initial excitation by visible light into the singlet metal to ligand charge transfer state, the electronic transition to the high spin quintet state may undergo different pathways. Here we apply ultrafast XUV photoemission spectroscopy to track the low to high spin dynamics in the aqueous iron tris bipyridine complex, [Fe bpy 3]2 , by monitoring the transient electron density distribution among excited states with a femtosecond time resolution. Aided by first principles calculations, this approach enables to reveal unambiguously both the sequential and direct de excitation pathways from singlet to quintet state, with a branching ratio of 4.5 1