Crystal structures and solid-state luminescent properties of Eu(III), Gd(III) and Tb(III) complexes with hexafluoroacetylacetone and 4′-substituted terpyridine ligands

Six mononuclear lanthanide complexes [Ln(hfac)3(ptpy)] (Ln(III) = Eu (1), Gd (2), Tb (3)) and [Ln(hfac)3(ftpy)] (Ln(III) = Eu (4), Gd (5), Tb (6)), synthesized with 1,1,1,5,5,5-hexafluoroacetylacetone (hfac) as a first ligand and 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) or 4′-furan-2,2′:6′,2″-terpyridine (ftpy) as a second ligand, were characterized by elemental analyses, infrared spectroscopy, single-crystal X-ray diffraction, and powder X-ray diffraction. Thermogravimetric analyses indicate that these ternary lanthanide complexes possess very good thermal stability. Solid-state samples of 1-Eu and 4-Eu exhibit characteristic red luminescence at CIE: 0.6721, 0.3276 and CIE: 0.6859, 0.3139, with absolute quantum yields of 59.95% and 83.14% and luminescence lifetimes of 0.819 and 0.727 ms, respectively. Solid-state samples of 3-Tb and 6-Tb display characteristic green luminescence at CIE: 0.2736, 0.7167 and CIE: 0.2674, 0.7219, with absolute quantum yields of 2.58% and 0.52% and luminescence lifetimes of 0.040 and 0.033 ms, respectively. The results suggest that terpyridine is a good sensitizer for Eu(III), while hfac is a good sensitizer for Tb(III). In solid-state, the synergistic sensitization effect of hfac and terpyridine is significant for Eu(III), but less for Tb(III). And the electron-donating substituent at the 4′-position make terpyridine more suitable for the sensitization of Eu(III), but unfavorable for Tb(III).