An intensive green emitting terbium complex using a newly designed aromatic hyperbranched polyester as an efficient antenna ligand

Abstract

The main challenge in the development of luminescent lanthanide complexes lies in the design of organic ligands. Herein, a carboxyl-terminated aromatic hyperbranched polyester (CHBPE) ligand was designed and synthesized, which has abundant branched end groups for chelating lanthanide ions, strong light-harvesting ability in the UV region, and more importantly, good energy match with the Tb³⁺ ion. The structure of CHBPE was characterized by MALDI-TOF MS, elemental analysis, FTIR, ¹H NMR, ¹³C NMR, and UV-Vis absorption measurements. Subsequently, a Tb³⁺ complex (CHBPE-Tb³⁺-Phen) based on CHBPE was obtained, in which Phen was used as a co-ligand to protect Tb³⁺ ions and reduce non-radiative transition of Tb³⁺ ions. The as-prepared complex was analyzed by MALDI-TOF MS, elemental analysis, ¹³C NMR, FTIR and UV-Vis methods. The results demonstrated that both CHBPE and Phen coordinated to Tb³⁺ ions and a stable chelate structure was formed. The synergistic effect of CHBPE and Phen made the complex exhibit remarkably strong green luminescence corresponding to the Tb³⁺ ion upon UV excitation. The efficiency of energy transfer (Φ_sen) from the CHBPE to Tb³⁺ ion was 55.2%, revealing that CHBPE is well suitable for the sensitization of Tb³⁺ ions. The absolute quantum efficiency (Φ_overall) and luminescence lifetime (τ_obs) of the complex were 27.5% and 0.28 ms, respectively. The possible energy transfer pathways in the complex system were proposed. The complex is expected to have potential application in the near ultraviolet light emitting diode (NUV-LED).