Perfluorinated dibenzoylmethane in Ln 3+ 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 Eu 3+ , Tb 3+ and Gd 3+ 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 Eu 3+ complex, this results in 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 Gd 3+ complex exhibits bright room-temperature phosphorescence -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.