Theoretical Study of the Light-Induced Spin Crossover Mechanism in [Fe(mtz)(6)](2+) and [Fe(phen)(3)](2+)

The deactivation pathway of the light-induced spin crossover process in two Fe(II) complexes has been studied by combining density functional theory calculations for the geometries and the normal vibrational modes and highly correlated wave function methods for the energies and spin orbit coupling effects. For the two systems considered, the mechanism of the photoinduced conversion from the low-spin singlet to the high-spin quintet state implies two intersystem crossings through intermediate triplet states. However, for the [Fe(mtz)(6)](2+) complex, the process occurs within few picoseconds and involves uniquely metal-centered electronic states, whereas for the [Fe(phen)(3)](2+) system the deactivation channel involves both metal to ligand charge transfer and metal-centered states and takes place in a femtosecond time scale.