Tuning the Emission of Homometallic Dy III , Tb III , and Eu III 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.

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(1 H -1,2,4-triazole-1-yl-methyl)-4-R-phenoxo, L R Tr (R = CH 3 ; 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 (T 1 ) states were estimated using low-temperature time-resolved emission spectra of Y III analogues. Compounds with L Cl Tr present higher emission intensity than those with L Me Tr. 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 Me Tr emits in the blue-to-white region, while the luminescence of DyL Cl Tr 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 S 1 → Ln III , a process that is less common as compared to T 1 → Ln III .