RESUMEN
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 π-π∗ transitions in 1,3-diketones. Moreover, both LLCT states provide sensitization of the Pr3+ luminescence involving the 3P0 and 3P1 levels.
RESUMEN
We performed spectroscopic investigations of a novel tris(1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)propane-1,3-dionato)(1,10-phenanthroline) holmium (III) complex. It was demonstrated that bonding the corresponding ligand environment to Ho3+ results in sensitization of the luminescence of the complex. The luminescence decay of the complex exhibits a biexponential behaviour. The short-lived component is attributed to the fluorescence of the ligand, whereas the long-lived component is connected with the Ho3+ emission. Using fluorescence lifetime imaging, it was shown that there is a single type of emission sites in the studied complex. Based on the results of the optical measurements, the energy diagram for the investigated Ho3+ complex was developed. It was shown that the energy transfer from the excited triplet level of the ligand environment to the 5F5 level of Ho3+ is responsible for the emission of the ion in the complex.