Electron dynamics in unoccupied molecular orbitals of two blue-light-emitting organic electroluminescent materials

Two candidate materials for blue organic electroluminescent devices, BAlq and DPVBi, were studied by time-resolved pump-and-probe photoelectron spectroscopy. The results were compared to green-light-emitting Alq. BAlq and DPVBi have LUMO peaks at about 3.7 eV above the HOMO, as compared to a value of 2.9 eV for Alq. All three materials exhibit very different decay properties of the LUMO, being slowest in Alq and increasingly faster in BAlq and DPVBi, being slowest in Alq and increasingly faster in BAlq and DPVBi.