Organic Light-Emitting Diodes Based on an Iron(III) Complex with Doublet Emission

Abstract

Because iron is the richest transition-metal element in the earth's crust, if iron complexes could be used as the emitters in organic light-emitting diodes (OLEDs), the cost of OLEDs would be reduced dramatically. Luminescent iron(III) complexes with low-spin d5electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge transfer (2MLCT) emission, but little attention has been paid to their application in OLEDs. Here, the first doublet-emission OLEDs based on an iron(III) complex, [Fe(phtmeimb)2]PF6, are demonstrated. Electroluminescent spectra of the optimized device remain stable as the voltage rises from 9 to 19 V and the maximum brightness exceeds 3000 cd/m2. Our results verify that 2MLCT emission can circumvent the problem of triplet exciton harvesting in closed-shell molecules. High performance OLEDs based on novel luminescent iron(III) complexes are anticipated.