Synthesis, photoluminescent features and intramolecular energy transfer mechanism of europium (III) complexes with fluorinate β-diketone ligand and auxiliary ligands

Abstract

Abstract A series of novel luminescent europium (III) complexes based on fluorinated β-diketone ligand 4,4-difluoro-1-phenyl-1,3-butanedione (DPBD) and auxiliary ligands 2,2-biquinoline (biq) or 1,10-phenanthroline (phen) or neocuproine (neo) or 2,2-bipyridyl (bipy) have been synthesized. The ligand DPBD with their complexes Eu(DPBD)3·(H2O)2 (C1), Eu(DPBD)3·biq (C2), Eu(DPBD)3·phen (C3), Eu(DPBD)3·neo (C4) and Eu(DPBD)3·bipy (C5) were confirmed by elemental analysis, infrared (IR) and proton nuclear magnetic resonance (NMR) spectroscopy. The crystalline nature, photoluminescence and thermal behavior were investigated by powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy and TG/DTA-DSC respectively. The emission spectra of complexes showed the characteristics sharp bands in solid state corresponding to 5D0–7Fj (j = 0–3) transition of europium ion with 5D0–7F2 as the most intense transition. The emission spectra, energy transfer mechanism, luminescence decay time and relative quantum efficiency clearly reveals that these photophysical properties are greatly influenced by the π-conjugated system, stability of the complexes and the efficient energy transfer from DPBD ligand to emitting level of Eu3+ ion. The complex Eu(DPBD)3·bipy (C5) exhibited highest quantum efficiency, luminescence intensity bearing good CIE color coordinates (x = 0.64 and y = 0.34) matching the NTSC (National Television Standard Committee) standard values for the pure red color and longest lifetime which makes it a promising red-emitting component for display devices.