Amorphous diphenylaminofluorene-functionalized iridium complexes for high-efficiency electrophosphorescent light-emitting diodes

Two new phosphorescent iridium(III) cyclometalated complexes, [Ir(DPA-Flpy)3] (1) and [Ir(DPA-Flpy)2(acac)] (2) ((DPA-Flpy)H = (9,9-diethyl-7-pyridinylfluoren-2-yl)diphenylamine, Hacac = acetylacetone), have been synthesized and characterized. The incorporation of electron-donating dipheoylamjao groups to the fluorene skeleton is found to increase the highest occupied molecular orbital (HOMO) levels and add hole-transporting ability to the phosphorescent center. Both complexes are highly amorphous and morphologically stable solids and undergo glass transitions at 160 and 153 °C, respectively. These iridium phosphors emit bright yellow to orange light at room temperature with relatively short lifetimes (< 1 μs) in both solution and the solid state. Organic light-emitting diodes (OLEDs) fabricated using 1 and 2 as phosphorescent dopant emitters constructed with a multilayer configuration show very high efficiencies. The homoleptic iridium complex 1 is shown to be a more efficient electrophosphor than the heteroleptic congener 2. Efficient electrophosphorescence with a maximum external quantum efficiency close to 10 % ph/el (photons per electron), corresponding to a luminance efficiency of ∼ 30 cd A-1 and a power efficiency of - 21 lm W-1, is obtained by using 5 wt.-% 1 as the guest dopant. KGaA.