Efficient Green-Light-Emitting Electrochemical Cells Based on Ionic Iridium Complexes with Sulfone-Containing Cyclometalating Ligands

A new approach to obtain green-emitting iridium(III) complexes is described. The synthetic approach consists of introducing a methylsulfone electron-withdrawing substituent into a 4-phenylpyrazole cyclometalating ligand in order to stabilize the highest-occupied molecular orbital (HOMO). Six new complexes have been synthesized incorporating the conjugate base of 1-(4-(methylsulfonyl)phenyl)-1H-pyrazole as the cyclometalating ligand. The complexes show green emission and very high photoluminescence quantum yields in both diluted and concentrated films. When used as the main active component in light-emitting electrochemical cells (LECs), green electroluminance is observed. High efficiencies and luminances are obtained at low driving voltages. This approach for green emitters is an alternative to the widely used fluorine-based substituents in the cyclometalating ligands and opens new design possibilities for the synthesis of green emitters for LECs.