Impact of ligand-centered excited states on luminescence sensitization in Pr3+ complexes with β-diketones

In this study, two novel Pr3+ complexes with different 1,3-diketonate ligands were synthesized and investigated. To study the effect of the ancillary ligand on the energy transfer mechanisms in the complexes, a phenanthroline ligand was introduced. To take into account the influence of the ligand environment composed of different ligands on the energy transfer and relaxation processes, we compared the synthesized compounds with a similar complex containing the phenanthroline ligand. The spectroscopic studies in the visible and near-infrared spectral regions were supplemented with DFT and TD-DFT calculations. We found two ligand-to-ligand charge transfer (LLCT) states, with one state corresponding to energy transfer between 1,3-diketones and the other - to energy transfer from the 1,3-diketone to the phenanthroline motif. It was demonstrated that optical excitation via the latter channel leads to a fourfold increase in the luminescence quantum yield as compared with excitation via the pi-pi* transitions in 1,3-diketones. Moreover, both LLCT states provide sensitization of the Pr3+ luminescence involving the P-3(0) and P-3(1) levels. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Two novel Pr3+ complexes with different 1,3-diketonate ligands were synthesized and studied in this research. Introduction of a phenanthroline ligand was found to significantly enhance the luminescence quantum yield by fourfold. The study identified two ligand-to-ligand charge transfer (LLCT) states and demonstrated their roles in sensitizing Pr3+ luminescence involving P-3(0) and P-3(1) levels.