Green Phosphorescence and Electroluminescence of Sulfur Pentafluoride-Functionalized Cationic Iridium(III) Complexes

We report on four cationic iridium­(III) complexes [Ir­(C^N)2(dtBubpy)]­(PF6) that have sulfur
pentafluoride-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 in the range of 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 so than 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 nm to 520 nm and with
an external quantum efficiency (EQE) of up to 1.7% in solution-processed
devices.