Investigations of luminescent behavior and intramolecular energy transfer mechanism of europium(III) complexes with fluorinated β-ketoester ligand

Abstract A fluorinated β-ketoester ligand, ethyl-(2-fluorobenzoyl) acetate (EFBA) has been employed to synthesized new europium binary and ternary complexes with ancillary ligands neocuproine (neo), bathophenanthroline (batho), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy) in high yield by the solution precipitation method. The ligand (EFBA) and the synthesized complexes Eu(EFBA) 3 ·(H 2 O) 2 (C1), Eu(EFBA) 3 ·neo (C2), Eu(EFBA) 3 ·batho (C3), Eu(EFBA) 3 ·phen (C4), Eu(EFBA) 3 ·bipy (C5) were characterized by elemental analysis, 1 H NMR, IR, UV–vis, thermal analysis (TG/DTG) and luminescence spectroscopy. The thermal analysis results show that the complex is stable up to 231 °C temperature which is sufficient for the normal working of OLEDs. The luminescence measurements indicate that π electron rich organic ligand ethyl-(2-fluorobenzoyl) acetate possessing high absorption coefficient acts as a suitable chromophoric moiety for the transfer of energy to the central Eu 3+ ion by the process of sensitization, this results in strong emissions band in red spectral region attributed to electric dipole 5 D 0  →  7 F 2 transition of europium ion. The luminescence intensity further enhanced by the introduction of N-containing ancillary ligands neocuproine, bathophenanthroline, 1,10-phenanthroline, and 2,2-bipyridyl in the ternary complexes C2–C5 because these ligands replace the solvent molecule in the coordination sphere and satisfy the coordination number around central europium ion. The sensitization process in europium complexes is investigated through the proposed energy transfer mechanism. The decay curves observations show the similar chemical environment around the europium ion in all the complexes.