Highly Efficient Blue-Green and White Light-Emitting Electrochemical Cells Based on a Cationic Iridium Complex with a Bulky Side Group

Blue-green-emitting cationic iridium complex with high luminescent efficiencies in both solutions and solid-states are essential for high-performance white light-emitting electrochemical cells (LECs). We report here an efficient blue-green-emitting cationic iridium complex [Ir(dfppz)(2)(tp-pyim)]PF6, using 1-(2,4-difluorophenyl)-1H-pyrazole (dfppz) as the cyclometalated ligand and 2-(1-(4-tritylphenyl)-1H-imidazol-2-yl)pyridine (tp-pyim) as the ancillary ligand. [Ir(dfppz)(2)(tp-pyim)]PF6 emits efficient blue-green light with a luminescent quantum yield of 0.54 in CH3CN solution. Because of the sterically bulky group 4-tritylphenyl that is attached to the ancillary ligand, the intermolecular interaction and excited-state self-quenching of [Ir(dfppz)(2)(tp-pyim)]PF6 in solid states is significantly suppressed. Theoretical calculations reveal that the emission from [Ir(dfppz)(2)(tp-pyim)]PF6 has both metal-to-ligand charge-transfer and ligand-centered (3)pi-pi* character. LECs based on [Ir(dfppz)(2)(tp-pyim)]PF6 show highly efficient blue-green electroluminescence with peak current efficiency, external quantum efficiency, and power efficiency of 18.3 cd A(-1), 7.6%, and 18.01m W-1, respectively. White LECs based on [Ir(dfppz)(2)(tp-pyim)PF6 give warm-white light, with Commission Internationale de L'Eclairage coordinates of (0.37, 0.41), a color-rendering index up to 80, and a peak power efficiency of 11.2 lm W-1.