10.1021/ja804506h.s001 Belén Ordejón Belén Ordejón Coen de Graaf Coen de Graaf Carmen Sousa Carmen Sousa Light-Induced Excited-State Spin Trapping in Tetrazole-Based Spin Crossover Systems American Chemical Society 2008 triplet state equilibrium distance tz vibrational mode LIESST mechanism Spin transition metal Equilibrium distances FeIII show absorption energies quintet state vibrational states intersystem 2008-10-22 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Light_Induced_Excited_State_Spin_Trapping_in_Tetrazole_Based_Spin_Crossover_Systems/2905825 Ab initio calculations have been performed on Fe<sup>II</sup> (tz)<sub>6</sub> (tz = 1-<i>H</i>-tetrazole) to establish the variation of the energy of the electronic states relevant to (reverse) light-induced excited-state spin trapping (LIESST) as function of the Fe−ligand distance. Equilibrium distances and absorption energies are correctly reproduced. The deactivation of the excited singlet is proposed to occur in the Franck−Condon region through overlap of vibrational states with an intermediate triplet state or an intersystem crossing along an asymmetric vibrational mode. This is followed by an intersystem crossing with the quintet state. Reverse LIESST involves a quintet−triplet and a triplet−singlet intersystem crossing around the equilibrium distance of the high-spin state. The influence of the transition metal is studied by changing Fe<sup>II</sup> for Co<sup>II</sup>, Co<sup>III</sup>, and Fe<sup>III</sup>. The calculated curves for Fe<sup>III</sup> show remarkable similarity with Fe<sup>II</sup>, indicating that the LIESST mechanism is based on the same electronic conversions in both systems.