Bright Yb3+ complexes for efficient pure near-infrared OLEDs

Abstract A series of neutral Yb3+ and Gd3+ complexes with isomeric 4,4,4-trifluoro-1-(naphthalenyl)butane-1,3-diones and 1,10-phenanthroline as an ancillary ligand were synthesized and characterized by a full range of analytical methods, including elemental analysis, FTIR and NMR spectroscopy, single crystal X-ray analysis, cyclic voltammetry (CVA) and thermal analysis (TG/DTA). Moreover, the unexpected formation of a mixed diketonate-carboxylate Yb3+ complex [Yb(2-Naph)2(CF3COO)(phen)(H2O)] from [Yb(2-Naph)3(phen)] in solution was observed. The photoluminescence quantum yield (PLQY) for complex [Yb(2-Naph)3(phen)] in the near infra-red region (one band with a peak at 980 nm) was about 3,2%. This value is close to the highest one reported for 1,3-diketonate complexes of Yb3+ ion to date. The energy transfer process is discussed in details, based on the results of TD-DFT calculations and experimental photophysical measurements. These complexes were successfully used as emitters in multilayer OLEDs. The electroluminescence quantum efficiency corresponding to the sole band at 980 nm reached 0.042% with a maximum irradiance of 11 μW/cm2 at 8.5 V for [Yb(2-Naph)3(phen)] based device, which is unusually high for such type of emitters.