New Charge Transporting Host Material for Short Wavelength Organic Electrophosphorescence: 2,7-Bis(diphenylphosphine oxide)-9,9-dimethylfluorene

We report the synthesis, crystal structure, and photophysical and electroluminescent properties of a new charge transporting host material for short wavelength phosphor-doped organic light emitting devices (OLEDs) based on 2,7-bis(diphenylphosphine oxide)-9,9-dimethylfluorene (PO6). The PO moiety is used as a point of saturation between the fluorene bridge and the outer phenyl groups so that the triplet exciton energy of PO6 is 2.72 eV, similar to that of a dibromo substituted fluorene, but it is more amenable to vacuum sublimation and has good film forming properties. Computational analysis (B3LYP/6-31G*) predicts the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of PO6 to be lower by 1.5 and 0.59 eV, respectively, compared to a similar diphenylamino substituted derivative. In a simple bilayer OLED device, PO6 exhibits structured UV electroluminescence at a peak wavelength of 335 nm and structured lower energy emission with peaks at 380 and 397 nm, similar to the sol...