Design, synthesis, and photoluminescence studies of fluorinated β-diketonate complexes of Eu(III) and Tb(III) incorporating a substituted bipyridine ligand: Experimental and DFT insights

Lanthanide luminescence forms the base of key technologies in sensing, bioimaging, optoelectronics, and photonic devices. The europium(III) and terbium(III) complexes, in particular, act as efficient light converters, translating UV excitation into sharp red and green emissions. Maximizing quantum yield is therefore critical for sensitivity and device performance. Herein, a series of heteroleptic Ln(III) complexes based on the fluorinated 1,3-diketone (hfac) and bipyridine-type ancillary ligands was examined to assess the influence of ligand environment on emission efficiency. The reference [Eu(hfac)₃(bpy)] complex exhibits a solid-state photoluminescence quantum yield of 45%, which increases to 57% upon 4,4′-dimethyl substitution in [Eu(hfac)₃(dmbpy)]. The fluorinated hfac ligand effectively minimizes high-energy vibrational quenching, while methyl substitution on bipyridine further suppresses non-radiative decay. Photophysical parameters, including lifetimes, radiative and non-radiative rate constants, and Judd–Ofelt analysis, highlight tunable emissive behavior in solid, and solution state. The DFT calculations combined with advanced bonding analyses (NBO, EDA-ETS-NOCV, and LF-DFT) support the experimental observations, indicating pronounced metal–ligand interactions and thermodynamically stable coordination environment. The results position [Ln(hfac) 3 (dmbpy)] complexes as robust, high-efficiency emitters for next-generation optical materials.