Abstract
<jats:p> Ligand-to-metal charge transfer (LMCT) photocatalysts have emerged as powerful tools for photoredox catalysis, but the photophysics underlying their reactivity is still underexplored. Of particular interest is the quantification and assignment of the various photophysical deactivation pathways that prevent the formation of, or nonproductively consume, desirable photogenerated ligand radicals. In this work, we use variable excitation wavelength and variable temperature ultrafast transient absorption spectroscopy and ultrafast actinometry to disentangle the various pathways undertaken upon LMCT photoexcitation that compete with productive radical generation. Using a model LMCT photocatalyst, FeCl <jats:sub>4</jats:sub> <jats:sup>−</jats:sup> , our temperature dependent ultrafast actinometry results point to the key role of primary recombination on the subpicosecond timescale within the solvent cage that depletes usable Cl• prior to cage escape. Otherwise, the photophysical kinetics of FeCl <jats:sub>4</jats:sub> <jats:sup>−</jats:sup> bound electronic states are remarkably temperature insensitive over more than 50 K, pointing to near-barrierless relaxation dynamics among the LMCT and ligand field manifold. </jats:p>