Highly efficient blue phosphorescent and electroluminescent Ir(iii) compounds

Abstract

Three new Ir(III) compounds with deep-blue phosphorescence have been synthesized. These molecules have the general formula of Ir(C^∧N)₂(L^∧X), where C^∧N = 2′,6′-difluoro-2,3′-bipyridine (dfpypy) and L^∧X = ancillary ligand such as 2-picolinate, pic (1), acetylacetonate, acac (2), or dipivaloylmethanoate, dpm (3). The ancillary ligands have been found to significantly destabilize both HOMO and LUMO levels of the Ir(III) complexes, compared to Ir(dfpypy)₃, without significantly changing the phosphorescence energy. Compounds 1–3 emit bright blue phosphorescence with λ_max = 440–460 nm and quantum efficiencies of 0.60–0.95 in solution and the solid state. Double-layer electroluminescent devices using compounds 1–3 as the dopant, CDBP (4,4′-bis(9-carbazolyl)-2,2′-dimethylbiphenyl) as the host/hole transporting layer, and TPBi (1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene) as the electron transport layer have been fabricated. These EL devices show pure blue colour with high efficiency. The EL device of compound 3 at the doping level of 20 wt% shows the best performance with EQE of 10–15% at the brightness of 10–1000 cd m⁻² and the maximum current efficiency of 22 cd A⁻¹.