Orange Phosphorescent Iridium Complexes Chelated with Phenylbenzothiazolate Derivatives for White Organic Light-Emitting Diodes

Abstract

For the application to white organic light-emitting diodes (OLEDs), the iridium complexes containing phenylbenzothiazolate derivatives as main ligands were prepared and their photophysical properties were investigated. We introduced a series of substituted 2-phenylbenzothiazolate (pbt) ligands to the iridium complexes. Variation of the substituent (R) in the ligand backbones could lead to the emission color tuning of the complexes. As ancillary ligands, the anions of 2,3-diphenyl-4-methyl-quinoline-C-2,N (4-Me-2,3-dpq) and phenylpyridine (ppy) were chelated to the iridium center to complete 6-coodinate complexes. The iridium complexes prepared herein are Ir(pbt-R)(2)(4-Me-2,3-dpq) (pbt-R = 2-(4-R-phenylbenzothiazolate (R = H, OCH3, F); 4-Me-2,3-dpq = 2,3-diphenyl-4-methyl-quinolinate-C-2,N) and Ir(pbt-R) 2(ppy) (ppy = 2-phenylpyridinate). The PL spectra of the iridium complexes showed yellow to orange emission at 540-595 nm with some variation in luminescence maxima depending on the ancillary ligand rather than on the substituents of the main ligands. The electrochemical characteristics of the complexes were also investigated with cyclic voltammetry and the resulting energy gaps between HOMOs and LUMOs were consistent with the PL maxima. The electroluminescence (EL) properties of the new iridium complexes were studied as possible phosphors for the application to orange and white OLEDs.