“…193 The intersystem crossing (ISC) dynamics was then explored with the use of complementary probes, sensitive to different degrees of freedom, which strongly help investigating both ultrafast electronic and structural dynamics. 97,113,192,[194][195][196][197][198] A generic diagram of the potential energy curves of the various states of Fe(II)-based complexes is shown in Figure 9, as a function of the Fe-N bond length, which is supposed to be the reactive coordinate of the spin transition. 171 The MLCT states have nearly the same equilibrium distance as the ground state, in agreement with the results on Ru(II) complexes discussed above, 159 while the ligand field states 1,3 T, 5 T and 5 E have their equilibrium distances elongated by ~0.1 Å, ~0.2 Å, and ~0.3 Å, respectively, relative to the ground state bond distance.…”