Tuning the Emission of Homometallic DyIII, TbIII, and EuIII 1-D Coordination Polymers with 2,6-Di(1 H-1,2,4-triazole-1-yl-methyl)-4-R-phenoxo Ligands: Sensitization through the Singlet State

Abstract

This work reports the structural characterization and photophysical properties of Dy^III, Tb^III, and Eu^III coordination polymers with two phenoxo-triazole-based ligands [2,6-di(1H-1,2,4-triazole-1-yl-methyl)-4-R-phenoxo, L^RTr (R = CH₃; Cl)]. These ligands permitted us to obtain isostructural polymers, described as a 1D double chain, with Ln^III being nona-coordinated. The energies of the ligand triplet (T₁) states were estimated using low-temperature time-resolved emission spectra of Y^III analogues. Compounds with L^ClTr present higher emission intensity than those with L^MeTr. The emission of Tb^III compounds was not affected by the different excitation wavelengths used and was emitted in the pure green region. In contrast, DyL^MeTr emits in the blue-to-white region, while the luminescence of DyL^ClTr remains in the white region for all excitation wavelengths. On the other hand, Eu^III compounds emit in the blue (ligand) or red region (Eu^III) depending on the substituent of the phenoxo moiety and excitation wavelength. Theoretical calculations were employed to determine the excited states of the ligands by using time-dependent density functional theory. These calculations aided in modeling the intramolecular energy transfer and rationalizing the optical properties and demonstrated that the sensitization of the Ln^III ions is driven via S₁ → Ln^III, a process that is less common as compared to T₁ → Ln^III.