In Situ Observation of Degradation by Ligand Substitution in Small-Molecule Phosphorescent Organic Light-Emitting Diodes

Solutions of facial-tris(1-phenylpyrazole)Ir(III) ( fac -Ir(ppz) 3 ), when dissolved in either tert -butyl isocyanide or in solid films of 2-naphthylisocyanide, undergo replacement of a ppz ligand by the isocyanide molecules after irradiation with UV light as demonstrated by liquid chromatograph mass spectrometer analysis. Similarly, solutions of Ir(ppz) 3 and bathophenanthroline (BPhen) in CH 2 Cl 2 or acetone- d 6 form a brightly emissive species, [Ir(ppz) 2 (Bphen)] + when irradiated with UV light as established by optical, mass, and 1 H nuclear magnetic resonance spectroscopy. Electroluminescent data from blocked organic light-emitting diode (OLED) devices demonstrate that both mer - and fac -(Ir(ppz) 3 ) dissociate a ligand and coordinate a neighboring BPhen molecule when the device is operated at moderate to high current levels. These experiments offer direct evidence of the dissociation of a metal–ligand bond and subsequent ligand substitution as a degradation pathway in active OLED devices during operation and provide a route to assay in situ the stability of future dopants.