Electroluminescence and hyperphosphorescence from stable blue Ir(III) carbene complexes with suppressed efficiency roll-off

Abstract

Abstract Efficient Förster energy transfer from a phosphorescent sensitizer to a thermally activated delayed fluorescent terminal emitter constitutes a potential solution for achieving superb blue emissive organic light-emitting diodes (OLEDs), which are urgently needed for high-performance displays. Herein, we report the design of four Ir(III) metal complexes, f-ct1a ‒ d, bearing functionalized imidazo[4,5-b]pyrazinylidene fragments that are supported by an aryl cyclometalate, a vertically arranged N-aryl appendage, and two peripheral tert-butyl substituents. These Ir(III) phosphors exhibit efficient true-blue emissions and a fast radiative decay lifetime. More importantly, they also undergo facile isomerization in the presence of catalysts (NaOAc and TsOH) at elevated temperature and, hence, allow for the mass production of either emitter by chromatographic separation, followed by thermal recycling of other isomers. One OLED device with doped f-ct1c shows a peak wavelength at 472 nm and a maximum external quantum efficiency (EQE) of 20.0%. Upon introduction of the terminal emitter ν-DABNA, the resulting hyper-OLED exhibits a true-blue color (CIEy = 0.11), a FWHM of 18 nm, a maximum EQE of 35.5% and a high EQE of 20.3% at 5000 cd m‒2, paving the way for innovative blue OLED technology.