A theoretical protocol to study the sensitization and emission mechanism in lanthanide compounds on the basis of multireference CASSCF/PT2 calculations is proposed and applied to [Eu(NO<sub>3</sub>)<sub>3</sub>(dppz-CN)] and [Eu(NO<sub>3</sub>)<sub>3</sub>(dppz-NO<sub>2</sub>)] compounds synthesized and characterized herein. The method consists of a fragmentation scheme where both the ligand and the lanthanide fragments were calculated separately but at the same level of theory, using ab initio wave-function-based methods which are adequate for the treatment of quasi-degenerate states. This is based on the fact that the absorption is ligand-localized and the emission is europium-centered. This characteristic allowed us to describe the most probable energy transfer pathways that take place in the complexes, which involved an ISC between the S<sub>1</sub> to T<sub>1</sub> ligand states, energy transfer to <sup>5</sup>D<sub>2</sub> in the lanthanide fragment, and further <sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>J</sub> emission. For both compounds, the triplet and <sup>5</sup>D<sub>2</sub> states were determined at the CASPT2 level to be around ∼26000 and ∼22400 cm<sup>–1</sup>, respectively. This difference is in the optimal range for the energy transfer process. Finally, the emissive state <sup>5</sup>D<sub>0</sub> was found at ∼18000 cm<sup>–1</sup> and the emission bands in the range 550–700 nm, in quite good agreement with the experimental results
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