Excited state properties of a [FeFe] hydrogenase active site models. The Time-Dependent Density Functional Theory theoretical picture

Recently a growing interest in the photochemical aspects of [FeFe] hydrogenases catalytic site and their biomimetic models has emerged. The photochemical aspects investigated range from the CO photolysis of the CO inhibited form of the enzyme to the excited state properties of the H-cluster models. [1] Regarding this last point, many efforts have been devoted to the investigation of the photochemical properties of simple diiron models of the [FeFe] hydrogenases catalytic site. The present contribution is focused on the Time-Dependent Density Functional theory (TDDFT) investigation of CO photolysis and photoisomerization of the trimetilphosphine (PMe3) derivative Fe2(S2C2H4)(CO)4(PMe3)2 starting from the recent ultrafast time-resolved infrared spectroscopy measurements [2,3]. By exploring the potential energy surfaces of low energy singlet excited states [4,5] the photoisomerization pathways has been characterized. Our calculation also show that the nature of this mechanism depends on the type of ligands coordinated to the iron atoms. The photoinduced CO dissociation involved excited states at higher excitation energy with the formation of a solvent adduct