A new series of luminescent tetrakis Ln3+-complexes with α-substituted β-diketonate ligands and Na+ as countercation

Abstract

The Ln3+ β-diketonate coordination compounds have received growing attention in the past few years, mainly due to their inherent huge variety of applications. The tris and tetrakis species have also been widely used as an emitting layer in organic light-emitting diodes (OLEDs) due to their high intensity and monochromatic emission. The tetrakis complexes usually present improved properties such as thermal and chemical stabilities, besides higher luminescence lifetimes than its correspondent tris complexes. Moreover, the commonly hydrated tris Ln3+-complexes show a luminescence quenching due to vibronic coupling between H2O molecules and the Ln3+ principal emitting levels (e.g., 4G5/2, 5D0, 5D4, 4F9/2 and 1G4 of the Sm3+, Eu3+, Tb3+, Dy3+ and Tm3+ ions, respectively) [1]. The acetylacetone (2,4-pentanedione) ligand, Hacac, is one of the most extensively used and studied β-diketonate ligands, especially for the Tb3+ ion. Nevertheless, the α-substituted Ln3+ β-diketonate complexes are relatively scarce in the literature [2]. Hence, this work reports the synthesis, characterization, and photoluminescent study of a new series of tetrakis coordination compounds containing the α-substituted β-diketonates 3-chloro acetylacetone (Cl-acac), presenting the general formula Na[Ln(Cl-acac)4], where Ln: Sm3+, Eu3+, Tb3+, Dy3+, and Tm3+. All complexes were characterized by elemental analysis, complexometric titration, thermal analysis, infrared absorption spectroscopy (FTIR), and X-ray powder diffraction (XPD). The Ln3+ complex photoluminescent properties (Figure 1) as well as the experimental intensity parameters (Ω2,4) of the Eu3+ were determined.