Tuning the Triplet Energy Levels of Pyrazolone Ligands to Match the 5D0 Level of Europium(III)

• Published in: Inorganic chemistry 2005-11, Vol.44 (24), p.8929-8936
• Main Authors: Shi, Mei, Li, Fuyou, Yi, Tao, Zhang, Dengqing, Hu, Huaiming, Huang, Chunhui
• Format: Article
• Language: English
• Subjects: Chemistry, Inorganic - methods; Crystallography, X-Ray; Electrons; Europium - chemistry; Ligands; Luminescence; Molecular Structure; Photochemistry - methods; Pyrazolones - chemical synthesis; Pyrazolones - chemistry; Spectrometry, Fluorescence
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic050844p

Three pyrazolone-based ligands, namely 1-phenyl-3-methyl-4-(1-naphthoyl)-5-pyrazolone (HL1), 1-phenyl-3-methyl-4-(4-dimethylaminobenzoyl)-5-pyrazolone (HL2), and 1-phenyl-3-methyl-4-(4-cyanobenzoyl)-5-pyrazolone (HL3), were synthesized by introducing electron-poor or electron-rich aryl substituents at the 4-position of the pyrazolone ring. Their corresponding europium complexes Eu(L X )3(H2O)2 and Eu(L X )3(TPPO)(H2O) ( X = 1−3) were characterized by photophysical studies. The characteristic Eu(III) emission of these complexes with at most 9.2 × 10-3 of fluorescent quantum yield was observed at room temperature. The results show that the modification of ligands tunes the triplet energy levels of three pyrazolone-based ligands to match the 5D0 energy level of Eu3+ properly and improves the energy transfer efficiency from antenna to Eu3+, therefore enhancing the Eu(III) emission intensity. The highest energy transfer efficiency and probability of lanthanide emission of Eu(L1)3(H2O)2 are 35.1% and 2.6%, respectively, which opens up broad prospects for improving luminescent properties of Eu(III) complexes by the modification of ligands. Furthermore, the electroluminescent properties of Eu(L1)3(TPPO)(H2O) were also investigated.