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 diphenylamino 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 degrees C, respectively. These iridium phosphors emit bright yellow to orange light at room temperature with relatively short lifetimes (< 1 mu s) 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 similar to 30 cd A(-1) and a power efficiency of similar to 21 lm W-1, is obtained by using 5 wt.-% 1 as the guest dopant.