Highly Efficient Red-Emitting OLEDs Prepared from Nona-Coordinated Europium(III) Complexes

Abstract

We have designed and synthesized three nona-coordinated organoeuropium complexes (OEuCs) with the general formula [Eu(btfa)3(FurTerPy)] (Eu1), [Eu(btfa)3(ThioTerPy)] (Eu2), and [Eu(btfa)3(NapTerPy)] (Eu3) by employing a primary 4,4,4-trifluoro-1-phenyl-1,3-butanedione (btfa) antenna ligand and three functionalized 2,2′:6′,2″-terpyridine (TerPy) ligands bearing different electron-donating groups at the 4′ position, namely, FurTerPy = 4′-(furan-2-yl)-2,2′:6′,2″-terpyridine; ThioTerPy = 4′-(thiophen-2-yl)-2,2′:6′,2″-terpyridine; and NapTerPy = 4′-(naphthalen-1-yl)-2,2′:6′,2″-terpyridine. The detailed photophysical properties of Eu1, Eu2, and Eu3 were analyzed using both experimental and computational methods. By analyzing the experimental and time-dependent density functional theory (TD-DFT) data in conjunction with the Lanthanide Luminescence Software Package (LUMPAC), we further elucidated the energy transfer processes in the OEuCs. Finally, the complexes were tested as the emitting layer (EML) in a multilayered device to fabricate red organic light-emitting diodes (R-OLED). Through optimization and device engineering, we have achieved a remarkable electroluminescence (EL) performance of maximum current efficiency (ηc) = 12.32 cd/A, maximum power efficiency (ηp) = 11.73 lm/W, and maximum external quantum efficiency (EQEmax) = 10.20%, respectively, for the Eu3-based double-EML OLED. To the best of our knowledge, this is the highest reported overall EL performance among the OEuCs until now.

Syntheses, Crystal Structures, and Luminescence of Hexafluoroacetylacetone Dinuclear Lanthanide Complexes Bridged by “Back-to-Back” Bisterpyridine

“…Among the neutral ancillary ligands, tridentate terpyridine and its derivatives possessing higher binding affinities with metal ions than their bidentate counterparts can act as efficient Ln(III) emission sensitizers and organic linkers suitable for constructing efficient luminescent lanthanide complexes. ,− Recently, Ilmi et al found that the neutral [Eu(β-diketonate) 3 (terpyridine)] complexes displayed an outstanding electroluminescence (EL) performance that might find applications in the field of organic light-emitting diodes (OLEDs). , In our previous work, to investigate the synergistic sensitization effect of dual ligands and the influences of different substituents at the 4′-position of 2,2′:6,2″-terpyridine on the luminescence properties of Ln(III) center, the fluorinated β-diketone ligand, 1,1,1,5,5,5-hexafluoroacetylacetone (hfac) was chosen as primary ligand and 2,2′:6′,2″-terpyridine (tpy), 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) ligand with electron-withdrawing phenyl group and 4′-furan-2,2′:6′,2″-terpyridine (ftpy) with electron-donating furyl group at 4′-position were used as neutral ancillary ligands to construct mononuclear analogues [Ln(hfac) 3 (tpy)], [Ln(hfac) 3 (ptpy)], and [Ln(hfac) 3 (ftpy)]. , The solid-state photoluminescence lifetime (τ) and absolute quantum yield (QY) of these complexes were measured. The results suggest that terpyridine and its derivatives are good sensitizers for Eu(III), while hfac is a good sensitizer for Tb(III).…”