Efficient and bright blue-emitting phosphorescent materials

Abstract

A new type of ancillary ligand for blue-emitting heteroleptic iridium complexes has been successfully developed. New ligands, 3-(trifluoromethyl)-5-(pyridin-2-yl)-1,2,4-triazolate and 5- (pyridin-2-yl)-tetrazolate, show stronger blue-shifting power than that of the picolate of FIrpic (iridium (III) bis(4,6-difluorophenylpyridinato)picolate). Organic light-emitting diodes (OLEDs) fabricated with a new complex, FIrtaz (iridium (III) bis(4,6-difluorophenylpyridinato)(5-(pyridine-2-yl)-1,2,4-triazo- late) or FIrN4 ((iridium (III) bis(4,6-difluorophenylpyridinato)(5-(pyridin-2-yl)-tetrazolate), as the blue dopant in the host of mCP (1,3-bis(9-carbazolyl)benzene), exhibit near-saturated blue electrophos- phorescence with Commision Internale de l'Eclairage (CIEx,y) coordinates of (0.14, 0.18) and (0.15, 0.24), respectively. Organic phosphorophores have recently achieved one of the major breakthroughs in the area of organic light-emitting diodes (OLEDs). These materials can enhance the effi- ciency of electroluminescence (EL) by three-fold, for which the external quantum efficiency (EQE) is usually limited to ~5% for devices based on fluorescence emitters. Organic materials are mostly hydrocarbons that do not usually emit phosphorescent light from the triplet state, which is often a forbidden state. Heavy atoms, such as Ir, Os, and Pt, provide the effective spin-orbital coupling that partially relieves the forbidden transition. Among these metal complexes, Ir(ppy)3, ppy = 2-phenylpyridinato, is probably one of the most useful materials for OLED applications. Ir(ppy)3 gives green emission with high efficiency, and several other structural modifications have been attempted in the last decade for the required emitting material suitable in the fabrication of full-color OLED displays. 1 Although many green- and red-emitting iridium complexes have been suc- cessfully synthesized, 2 authentic blue-emitting iridium complexes for phosphorescent OLEDs are notably sparse (Scheme 1).