Dynamics of the Energy Transfer Process in Eu(III) Complexes Containing Polydentate Ligands Based on Pyridine, Quinoline, and Isoquinoline as Chromophoric Antennae

Albano N Carneiro Neto; Renaldo T Moura Jr; Luís D Carlos; Oscar L Malta; Martina Sanadar; Andrea Melchior; Elfi Kraka; Silvia Ruggieri; Marco Bettinelli; Fabio Piccinelli

doi:10.1021/acs.inorgchem.2c02330

Dynamics of the Energy Transfer Process in Eu(III) Complexes Containing Polydentate Ligands Based on Pyridine, Quinoline, and Isoquinoline as Chromophoric Antennae

Inorg Chem. 2022 Oct 17;61(41):16333-16346. doi: 10.1021/acs.inorgchem.2c02330. Epub 2022 Oct 6.

Authors

Affiliations

¹ Physics Department and CICECO-Aveiro Institute of Materials, University of Aveiro, 3810-193Aveiro, Portugal.
² Department of Chemistry and Physics, Federal University of Paraíba, 58397-000Areia, Brazil.
³ Department of Chemistry, Southern Methodist University, Dallas, Texas75275-0314, United States.
⁴ Department of Fundamental Chemistry, Federal University of Pernambuco, 50740-560Recife, Brazil.
⁵ Dipartimento Politecnico di Ingegneria e Architettura, Laboratorio di Tecnologie Chimiche, University of Udine, 33100Udine, Italy.
⁶ Luminescent Materials Laboratory, Department of Biotechnology, University of Verona and INSTM, UdR Verona, 37134Verona, Italy.

Abstract

In this work, we investigated from a theoretical point of view the dynamics of the energy transfer process from the ligand to Eu(III) ion for 12 isomeric species originating from six different complexes differing by nature of the ligand and the total charge. The cationic complexes present the general formula [Eu(L)(H₂O)₂]⁺ (where L = bpcd^2- = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate; bQcd^2- = N,N'-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate; and bisoQcd^2- = N,N'-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N'-diacetate), while the neutral complexes present the Eu(L)(H₂O)₂ formula (where L = PyC3A^3- = N-picolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetate; QC3A^3- = N-quinolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetate; and isoQC3A^3- = N-isoquinolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetate). Time-dependent density functional theory (TD-DFT) calculations provided the energy of the ligand excited donor states, distances between donor and acceptor orbitals involved in the energy transfer mechanism (R_L), spin-orbit coupling matrix elements, and excited-state reorganization energies. The intramolecular energy transfer (IET) rates for both singlet-triplet intersystem crossing and ligand-to-metal (and vice versa) involving a multitude of ligand and Eu(III) levels and the theoretical overall quantum yields (ϕ_ovl) were calculated (the latter for the first time without the introduction of experimental parameters). This was achieved using a blend of DFT, Judd-Ofelt theory, IET theory, and rate equation modeling. Thanks to this study, for each isomeric species, the most efficient IET process feeding the Eu(III) excited state, its related physical mechanism (exchange interaction), and the reasons for a better or worse overall energy transfer efficiency (η_sens) in the different complexes were determined. The spectroscopically measured ϕ_ovl values are in good agreement with the ones obtained theoretically in this work.