Vibrations tell the tale. A time-resolved mid-infrared perspective of the photochemistry of iron complexes

Owing to its superb structure-specificity, time-resolved infrared spectroscopy (TR-IR) has emerged in recent years as one of the most powerful tools for the exploration of photochemical dynamics in solution. It can be carried out in two distinct modes of operation: real-time Fourier-transform spectroscopy following flash photolysis or purely laser-based pump-probe spectroscopy. These two approaches combine to access nearly seamlessly a time window ranging from around hundred femtoseconds all the way up to hundreds of seconds. In this article, we highlight the most recent applications of these techniques in temporally resolving the multiscalar photochemical dynamics of iron complexes. The processes of interest here entail ligand dissociations or fragmentations, which lead to the formation of unique Fe-containing intermediates with remarkable electronic structure, exceptional molecular geometry, or unprecedented chemical reactivity. Thus, TR-IR can provide a novel unexpected view into the realm of iron chemistry including such fascinating topics like high-valent iron, ferracyclic compounds, or carbon dioxide binding to iron centers. Time-resolved infrared spectroscopies are used to elucidate multiscalar photochemical processes of iron complexes.