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 Im 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 Im W-1 without compromising the device stability.