Fluorinated Cationic Iridium(III) Complex Yielding an Exceptional, Efficient, and Long-Lived Red-Light-Emitting Electrochemical Cell

A carefully designed red-light-emitting iridium (III) cationic complex yields light-emitting electrochemical cells (LECs) with exceptional efficiency and stability. [Ir(4Fppy)2(biq)][PF6] (4Fppy = 2-(4-fluorophenyl)pyridinato, biq = 2,2′-biquinoline), whose structure was authenticated by single-crystal X-ray diffraction, emits in the red region of light with photoluminescence (upon 360 nm excitation) and electroluminescence maxima at 629 nm. Astonishingly, it is based on a fluorinated ligand, a design concept more commonly used for green emitter materials. Pairing it with a ligand that has comparatively low-lying frontier orbitals allows for a red shift of the band gap. The uncommon electronic structure of the complex allows overcoming the common problem of strong metal–ligand antibonding interactions in the excited state, rendering it extremely stable under operation. The complex displays a high photoluminescence quantum yield of 27.1% giving rise to an extremely efficient LEC with an initial maximum luminance of 326 cd m–2, current efficiency of 3.26 cd A–1, and power efficiency of 2.27 lm W–1, surpassing the current state of the art. Remarkably, the efficient red LEC has a lifetime of 167 h when driven under a block-wave pulsed current at a frequency of 1000 Hz, an average current density of 100 A m–2, and a duty cycle of 50%. Increasing the duty cycle to 75% led to a decrease in the device average voltage, increasing the power efficiency to an exceptional value of 2.97 lm W–1 without compromising the device stability.