Green phosphorescence and electroluminescence of sulfur pentafluoride-functionalized cationic iridium(III) complexes

We report four cationic iridium(III) complexes [Ir(C^N)₂(dtBubpy)](PF₆) that have sulfurpentafluoride-modified 1-phenylpyrazole and 2-phenylpyridine cyclometalating (C^N) ligands (dtBubpy = 4,4'-di-tert-butyl-2,2'-bipyridyl). Three of the complexes were characterized by single-crystal X-ray structure analysis. In cyclic voltammetry, the complexes undergo reversible oxidation of iridium(III) and irreversible reduction of the SF₅ group. They emit bright green phosphorescence in acetonitrile solution and in thin films at room temperature, with emission maxima between 482–519 nm and photoluminescence quantum yields of up to 79%. The electron-withdrawing sulfur pentafluoride group on the cyclometalating ligands increases the oxidation potential and the redox gap and blue-shifts the phosphorescence of the iridium complexes more than do the commonly-employed fluoro and trifluoromethyl groups. The irreversible reduction of the SF₅ group may be a problem in organic electronics; for example, the complexes do not exhibit electroluminescence in light-emitting electrochemical cells (LEECs). Nevertheless, the complexes exhibit green to yellow-green electroluminescence in doped multilayer organic light-emitting diodes (OLEDs) with emission maxima ranging from 501–520 nm and with an external quantum efficiency (EQE) of up to 1.7% in solution-processed devices.