Transient absorption spectroscopy of the [Fe(2 CH3-phen)3]2+ complex: Study of the high spin ↔ low spin relaxation of an isolated iron(II) complex

► We studied optical excitation of [Fe(2 CH3 phen)3]2+ complex in solution. ► A Short pump pulse centered at λ = 500 nm switches at the spin state of ∼100% of the complex from the low spin (S = 0) state to the high spin (S = 2) state. ► A Short pump pulse centered at λ = 300 nm switches the spin state of ∼20% of the complex from the high spin (S = 2) state to the low spin (S = 0) state. ► At λ = 300 nm, ∼80% of the photo-excited complexes are transiently photo-dissociated. ► All these photo-switchings occur in less than 500 femtoseconds.