Perfluorinated dibenzoylmethane in Ln3+ complexes: charge-transfer quenching and implications for luminescence design

Abstract

Perfluorination of ligands is commonly employed to enhance the luminescence efficiency of Ln³⁺ coordination compounds by reducing C–H vibrational quenching. In this study, we challenge this chemical design strategy by synthesizing and investigating a series of Eu³⁺, Tb³⁺ and Gd³⁺ complexes with 1,3-bis(perfluorophenyl)propane-1,3-dione. Comprehensive spectroscopic analysis including steady-state, time-resolved and ultrafast transient absorption spectroscopy has revealed that fluorination induces charge-transfer state quenching that competes with ion-centered emission. In the Eu³⁺ complex, this results in the reduced energy transfer efficiency and lower luminescence quantum yields compared to its non-fluorinated analogue – the sensitization efficiency drops from 0.47 to 0.01. Surprisingly, the perfluorinated Gd³⁺ complex exhibits bright room-temperature phosphorescence, which is an exceptionally rare and valuable effect in lanthanide coordination compounds. By uncovering the nuanced interplay between ligand structure and excited-state dynamics, this work provides new insights for the rational design of advanced luminescent materials.