Complexes that have access to d orbitals are able to access spin multiplicities besides the singlet and triplet states, as some complexes have orbitals of similar or degenerate energies so that it is energetically favorable for electrons to be unpaired. It is possible then for a single complex to undergo multiple intersystem crossings, which is the case in light-induced excited spin-state trapping (LIESST), where, at low temperatures, a low-spin complex can be irradiated and undergo two instances of intersystem crossing. For Fe(II) complexes, the first intersystem crossing occurs from the singlet to the triplet state, which is then followed by intersystem crossing between the triplet and the quintet state. At low temperatures, the low-spin state is favored, but the quintet state is unable to relax back to the low-spin ground state due to their differences in zero-point energy and metal-ligand bond length. The reverse process is also possible for cases such as [Fe(ptz) 6 ](BF 4) 2, but the singlet state is not fully regenerated, as the energy needed to excite the quintet ground state to the necessary excited state to undergo intersystem crossing to the triplet state overlaps with multiple bands corresponding to excitations of the singlet state that lead back to the quintet state.