Unfolding the Photophysical Behavior of Luminescent Polymeric Films Containing β-Diketonate Tetrakis Eu^III Complexes via Multilayer Quantum Mechanics

The elucidation of the mechanisms governing the photophysical properties of trivalent lanthanide (Ln^III) complexes embedded in polymeric matrices, such as poly-(methyl) methacrylate (PMMA) and polyvinylidene fluoride (PVDF), is challenging due to their intricate composite nature. Although theoretical modeling offers insights into film luminescence, conventional computational strategies face significant limitations. Given the large-scale nature of these systems, which encompass thousands of atoms, full-scale quantum mechanical (QM) simulations are impractical. Existing methodologies often integrate molecular mechanics (MM) with QM, yet such hybrid frameworks introduce inaccuracies in excited-state calculations. To address these challenges, this study proposes a multilevel computational protocol employing a hybrid QM/QM approach. Density functional theory (DFT) was used for the [Eu-(dbm)₄]^- complex (dbm = 1,3-diphenyl-1,3-propanedione), while the polymeric environment was treated using the GFNn-xTB method. The protocol demonstrated strong agreement between experimental and theoretical emission quantum yields (QY) for both the isolated complex and [Eu-(dbm)₄]^-/PMMA or PVDF films. Our findings revealed that angular and length distortions in the Eu-O bonds within PVDF were induced by increased packing around the complex, impacting the ligand-Eu^III energy transfer by elevating the triplet state energy. These results underscore the predictive capabilities of the hybrid QM/QM strategy, offering a robust alternative for deciphering opto-structural relationships in Ln^III-based polymeric films.