New Strategies to Improve the Efficiency of Curcumin-Based Iridium Complexes for OLED Devices

Among the solid-state lighting technologies, OLEDs occupy a prominent position for the high efficiencies associated with the low CO2 emissions. In line with the recent studies aimed at designing sustainable and biodegradable devices, herein we report on the synthesis of a series of iridium(III) complexes featuring, as β-diketone ligands, curcumin and 6-dehydrogingerdione, two natural compounds found in the rhizome of Curcuma longa and Zingiber officinale. To improve the solubility of both the ligands and prevent the aggregation of the complexes, oleoyl residues were inserted on the phenolic −OH groups. The resulting complexes exhibited a green emission with quantum yields as high as 2.8 % (relative to fluorescein). OLED devices were fabricated by using, as emitting layer, a host-guest blend of the iridium complex in 4,4’-bis(N-carbazolyl)-1,1’-biphenyl (CBP). The morphological analysis revealed that thin films of the emitting layer were homogeneous. The devices fabricated with iridium complexes from 6-dehydrogingerdione exhibited higher luminance, efficiency and power efficiency with respect to the corresponding devices obtained from curcumin; also the functionalization of the β-diketone unit with the oleoyl residue proved to increase significantly the performance of the device. Overall, these data suggest that aggregation is a key factor that compromise the performances of the corresponding OLEDs.