US Patent 7851072 Stable and efficient electroluminescent materials

An organic light emitting device is provided. The device has an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer may include a molecule of Formula I wherein an alkyl substituent at position R′5 results in high efficiency and operational stability in the organic light emitting device. Additionally or alternatively, the emissive layer may include a metal-ligand complex in which the ligand is an aryl or alkyl substituted phenylpyridine ligand.