The synthesis of di-orthometallated triphenyl phosphite iridium(III) complexes with steric groups and their application in OLEDs

Abstract

A series of di-orthometallated triphenyl phosphite iridium(III) complexes [Ir(tdbpit)(bpy)Cl (1), Ir(tdbpit)(dbbpy)Cl (2), Ir(tdbpit)(sb)Cl (3) (tdbpitH2 = tris (2,4-di-tert-butylphenyl) phosphite, bpy = 2,2′-bipyridine, dbbpy = 4,4′-diterbutyl-2,2′-bipyridine, sb = 4,5-diaza-9,9′-spirobifluorene)] with steric groups had been synthesized and characterized. Single X-ray structural analyses were conducted on 2 and 3 to reveal their coordination arrangement. In CH2Cl2 solution, complexes 1–3 show strong yellow-green phosphorescent emission at 569 nm, 562 nm and 559 nm, respectively. The observed emission lifetimes are between 1.39 μs and 1.54 μs, together with quantum yields between 0.31 and 0.63 in PMMA film. The extra steric groups on the diimine ligands had obviously increased the quantum yields by decreasing the intermolecular interaction. Using these iridium(III) complexes as dopant, the OLEDs show good performance at 15 wt% high doping concentration. OLED device based on complex 2 shows the highest luminous efficiencies of (10.1%, 32.5 cd A−1). Device based on complex 3 displays the highest peak luminance of 15990 cd m−2, and exhibits a maximum luminous efficiency of 31.5 cd A−1 with an external quantum efficiency of 9.6% and small efficiency roll-off values. At a practical luminance of 1000 cd m−2, the efficiency values are maintained as high as 9.0% and 29.5 cd A−1. The results show that the sterically hindered tert butyl and spirofluorene spacers in these phosphor molecules can effectively reduce the self-quenching.