Deep-blue phosphorescent iridium(III) dyes based on fluorine-functionalized bis(2,3′-bipyridyl) ligand for efficient organic light-emitting diodes

Abstract

Four blue phosphorescent complexes with the general formula (4-R-dfpypy)2Ir(LˆX), where 4-R-dfpypy = 4-alkyl-2ʹ,6ʹ-difluoro-2,3ʹ-bipyridine and LˆX = picolinate or dipivaloylmethanate, were synthesized, and their photoluminescent properties were systematically investigated. All complexes show bright deep-blue phosphorescence emissions with λmax = 440–450 nm and quantum efficiencies of 0.25–0.78 in the fluid state. The emission bands of compounds 1–4 are slightly red shifted by 5–10 nm relative to the homoleptic congener, Ir(dfpypy)3. Electroluminescent (EL) devices were fabricated using compound 2 as a dopant, 1,3-bis(N-carbazolyl)benzene (mCP) as the host, and TSPO1 (diphenylphosphineoxide-4-(triphenylsilyl)phenyl) as the electron transporting/exciton blocking layer. These EL devices show a deep-blue color (CIE: x, y = 0.14, 0.17) with high efficiencies. The EL device of compound 2 at a doping level of 5 wt% has the best performance with an EQE of 14.6% at a brightness of 100 cd/m2 and a current efficiency of 18.3 cd/A.