%0 Journal Article %A Marino, Andrea %A Chakraborty, Pradip %A Servol, Marina %A Lorenc, Maciej %A Collet, Eric %A Hauser, Andreas %T The role of ligand-field states in the ultrafast photophysical cycle of the prototypical iron(II) spin-crossover compound [Fe(ptz)6](BF4)2 %J Angewandte Chemie International Edition %@ 1433-7851 %V 53 %N 15 %P 3863-3867 %D 2014 %K intersystem crossing %K LIESST %K ligand-field states %K spin crossover %K ultrafast spectroscopy %U http://onlinelibrary.wiley.com/doi/10.1002/anie.201310884/abstract %R 10.1002/anie.201310884 %U http://archive-ouverte.unige.ch/unige:38562 %X Light-induced excited spin state trapping (LIESST) in iron(II) spin-crossover compounds, i.e., the light-induced population of the high-spin (S=2) state below the thermal transition temperature, was discovered thirty years ago. For irradiation into metal-ligand charge transfer (MLCT) bands of the low-spin (S=0) species the acknowledged sequence takes the system from the initially excited 1MLCT to the high-spin state via the 3MLCT state within ~150 fs, thereby bypassing low-lying ligand-field (LF) states. Nevertheless, these play role, as borne out by the observation of LIESST and reverse-LIESST on irradiation directly into the LF bands for systems with only high-energy MLCT states. Herein we elucidate the ultrafast reverse-LIESST pathway by identifying the lowest energy S=1 LF state as intermediate state with a lifetime of 39 ps for the light-induced high-spin to low-spin conversion on irradiation into the spin-allowed LF transition of the high-spin species in the NIR.