Transferable Semiempirical Models for Judd–Ofelt Parameters and Multiphonon Relaxation in Eu ³⁺ Complexes: Toward an Experiment‐Free Luminescence Design

The rational design of lanthanide‐based luminescent systems using purely theoretical approaches remains challenging due to the reliance of existing models on experimental data. Herein, we propose a theoretical protocol for the design of new Eu 3+ based luminescent systems, starting from a previously synthesized and experimentally characterized complex. The approach is based on two semiempirical models: (i) a combination of the QDC and BOM models for the calculation of Judd–Ofelt intensity parameters (Ω 2 and Ω 4 ) and (ii) a model based on the van Dijk–Schuurmans equation and Fermi's golden rule to estimate nonradiative emission rates ( A NR ) from radiative rates ( A R ). The model for calculating the Judd–Ofelt intensity parameters was parameterized using the [Eu 2 (Ibf) 6 (bpy) 2 ] complex as a reference and validated with the analogous complexes [Eu 2 (Ibf) 6 (4,4′‐dmbpy) 2 ] and [Eu 2 (Ibf) 6 (5,5′‐dmbpy) 2 ]. In contrast, due to its mathematical structure, the model for calculating A NR required the inclusion of all three systems in the parameterization set. The models reproduce the intensity parameters with average errors below 4% and the nonradiative rate with errors below 0.2%. The protocol was applied to eight new complexes obtained by substituting the bipyridine methyl group with NH 2 , NO 2 , OCH 3 , and OH at the 4,4′‐and 5,5′‐positions. The theoretical predicted luminescent properties indicate that methoxy‐substituted systems are predicted to exhibit superior performance, with predicted quantum yields of ~93.8%. This protocol provides a computationally efficient strategy for the rational design of Eu 3+ based luminescent materials.