Exploring the effect of fluorine radicals as substituents in (3-diketones on the luminescence properties of Eu3+complexes

For decades, researchers have utilized fluorination of ligand molecules in trivalent lanthanide ion (Ln3+) complexes as the chemical approach to suppress non-radiative relaxation processes. In this study, we provide a comprehensive analysis of the photophysical properties of europium Eu3+ acetylacetonate complexes bearing methyl (CH3) and trifluoromethyl (CF3) substituents. Our findings reveal that fluorination of the (3-diketone ligand exerts a multifaceted influence on its photophysical properties. Sequential replacement of CH3 with CF3 lowers the energies of both singlet and triplet excited states, thereby enhancing energy transfer efficiency from the ligand to the metal ion. Moreover, the replacement of CH3 with CF3 fundamentally alters the nature of the charge transfer state and significantly suppresses non-radiative vibrational relaxation. It leads to a remarkable increase in both intrinsic and overall luminescence quantum yield by an order of magnitude. This study establishes a foundation for designing highly luminescent Ln3+ complexes by unveiling previously unexplored characteristics of charge transfer states.