While high time-resolution TOAS data 5 is claimed to support the direct mechanism, XES, owing to its sensitivity to the TM spin state, clearly detects the involvement of a 3 MC state in the photorelaxation and thus indicates that the sequential pathway has to be operative. Furthermore, branching of the two mechanisms was proposed by a UV photoemission study. Theory has a great potential to rationalise ultrafast experiments and provide complementary insights. However, the description of full singlet-triplet-quintet dynamics is extremely challenging due to the simultaneous treatment of disparate spin states, as well as multidimensional dynamics. For the description of the light induced LS → HS dynamics in Fe(II) polypyridyl complexes, theoretical models have so far been limited to either the application of Fermi's golden rule, or quantum dynamics in exceedingly reduced dimensions. While these studies do deliver valuable mechanistic insights, the limitations of the utilised theories (e.g., neglecting nuclear motion or using less accurate electronic structure descriptions ) and large uncertainties in the calculated intersystem crossing (ISC) rates do not allow to lift the controversies in the experimental observations.