The present invention is an organic light emitting device (OLED) comprising an anode, a cathode and a luminescent region provided between the anode and the cathode. The luminescent region comprises an electron injection and transporting zone and at least one of a hole injection and transporting zone and a mixed charge transport layer. One or both of the electron injection and transporting zone and the mixed charge transporting layer comprises an azole compound represented by formula I and/or II. The provision of the novel azole compounds of the invention as electron transport materials within an organic electroluminescent device advantageously reduces power consumption and increases power conversion efficiency within the device and as such, are suitable for a variety of display applications.