Supramolecularly Caged Green-Emitting Ionic Ir(III)-Based Complex with Fluorinated C^N Ligands and Its Application in Light-Emitting Electrochemical Cells.

Abstract

Ionic Ir(III) complexes are the most promising emitters in light emitting electrochemical cells (LECs), especially in the high energy emission range for which it is difficult to find emitters with sufficient efficiencies and lifetimes. To overcome this challenge, we introduced the concept of intramolecular π-π stacking of an ancillary ligand (6-phenyl-2,2'-bipyridine, pbpy) in the design of a new green-emitting iridium ionic transition metal complex with a fluoro-substituted cyclometallated ligand, 2-(4-fluorophenyl)pyridinato (4Fppy). [Ir(4Fppy)2(pbpy)][PF6] has been synthesized and characterized and its photophysical and electrochemical properties have been studied. The complex emits green light with maxima at 561 and 556 nm under UV excitation from powder and thin film, respectively, and displays a high photoluminescence quantum yield (PLQY) of 78.5%. [Ir(4Fppy)2(pbpy)][PF6] based LECs driven under pulsed current conditions showed under an average current density of 100 A m-2 (at 50% duty cycle) a maximum luminance of 1443 cd m-2, resulting in 14.4 cd A-1 and 7.4 lm W-1 current and power efficiencies, respectively. A remarkable long device lifetime of 214 h was observed. Reducing the average current density to 18.5 A m-2 (at 75% duty cycle) led to an exceptional device performance of 19.3 cd A-1 and 14.4 lm W1- for current and power efficiencies, an initial maximum luminance of 352 cd m-2 and a lifetime of 617 h.