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

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 d(5) electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge trans-fer ((MLCT)-M-2) emission, but little attention has been paid to their application in OLEDs. Here, the first doublet-emission OLEDs based on an iron(III) com-plex, [Fe(phtmeimb)(2)]PF6, are demonstrated. Elec-troluminescent spectra of the optimized device remain stable as the voltage rises from 9 to 19 V and the maximum brightness exceeds 3000 cd/m(2). Our results verify that (MLCT)-M-2 emission can circum-vent the problem of triplet exciton harvesting in closed-shell molecules. High performance OLEDs based on novel luminescent iron(III) complexes are anticipated.