“…Metalloporphyrins (MPs) incorporating 3d transition metal ions with closed or open d-shells are primary reactants in biochemical energy cycles. − Building upon the first reports of porphyrin π-ring synthesis in the 1930s, , modern protocols have expanded the MP family to encompass most of the stable elements. − The so-called “MP periodic table” , rationalizes how the nature of the metal ion imparts unique photophysical properties, placing MPs at the focus of a cross-disciplinary research effort that targets the bioinspired production, conversion, transduction and storage of renewable energy. − In contrast, the integration of MPs containing transition metal ions with an open 3d-shell in photoconversion applications remains limited despite strong prospects associated with their coupled electronic and magnetic activities. This status can be traced back to the fact that, although the initial photoexcitation is delocalized over the porphyrin π-ring as for their closed-shell congeners, the pathways of intramolecular relaxation are rapidly obscured by the participation of intermediate states that involve the d-levels of the metal ions. − Several decades of investigations with electronic spectroscopy have shown that it is rarely possible to unambiguously differentiate (d,d), (π,d), and (d,π) states in the UV–visible and near-infrared spectral ranges. − Ultrafast techniques with inherent structural sensitivity such as time-resolved Raman spectroscopy (tr-RSS) − and, recently, time-resolved X-ray absorption spectroscopy (tr-XAS) on the picosecond (ps) and femtosecond (fs) time scales ,− are partially challenged by the lack of direct spin-sensitivity so that they tend to return highly correlated rate constants.…”