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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

By María J. Beltrán-Leiva (4237324), Plinio Cantero-López (4237327), César Zúñiga (4237330), Ana Bulhões-Figueira (4237333), Dayán Páez-Hernández (1524493) and Ramiro Arratia-Pérez (1524499)


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

Topics: 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
Year: 2017
DOI identifier: 10.1021/acs.inorgchem.7b01221.s001
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