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Theoretical Method for an Accurate Elucidation of Energy Transfer Pathways in Europium(III) Complexes with Dipyridophenazine (dppz) Ligand: One More Step in the Study of the Molecular Antenna Effect
Abstract
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- Text
- Journal contribution
- Biophysics
- Biochemistry
- Plant Biology
- Environmental Sciences not elsewhere classified
- Biological Sciences not elsewhere classified
- Mathematical Sciences not elsewhere classified
- Chemical Sciences not elsewhere classified
- Physical Sciences not elsewhere classified
- energy transfer pathways
- 5 D 2
- emissive state 5 D 0
- CASSCF
- fragmentation scheme
- emission mechanism
- Accurate Elucidation
- emission bands
- cm
- ISC
- energy transfer process
- ab initio wave-function-based methods
- quasi-degenerate states
- lanthanide fragments
- CASPT 2 level
- Molecular Antenna Effect
- 5 D 2 states
- lanthanide fragment
- T 1 ligand states
- lanthanide compounds
- energy transfer
- S 1
- Energy Transfer Pathways
- Eu
- Theoretical Method