Photoinduced dynamics in an exchange-coupled trinuclear iron cluster

Abstract We present a joint experimental and computational study of the trinuclear basic carboxylate iron complex Fe III 2 Fe II O ( CH 3 CO 2 ) 6 ( H 2 O ) 3 , which is a model system for understanding photoinduced ultrafast spin dynamics in magnetic iron-based transition metal oxides. We have carried out femtosecond optical transient absorption spectroscopy of molecules in solution at room-temperature exciting either at 400 or 520 nm and observed a long-lived excited-state absorption (ESA) signal from ca. 400–670 nm. The ESA signal is composed of several broad un-resolved bands at 405, 440 and 530 nm. The decay dynamics are complicated and three exponentials with corresponding decay time constants of τ 1 = 360 ± 30 fs, τ 2 = 5.3 ± 0.6 ps, τ 3 = 65 ± 5 ps and a constant offset ( τ 4 > 500 ps) were needed to fit the data over the full wavelength range. The data indicate that the lowest excited state is populated within the duration of the excitation pulse ( 120 fs). Highly correlated coupled-cluster calculations can satisfactorily reproduce the experimental vibrational spectrum and highlight the role of the μ 3 -oxo bridge connecting the Fe ions to create a highly correlated ground-state and identify the excited state as having a mixture of both charge-transfer and ligand-field/d-orbital characters.