A New Charge Transporting Host Material for Short Wavelength Organic Electrophosphorescence: 2,7–Bis(diphenylphosphine oxide)–9,9–dimethylfluorene
We report the synthesis, crystal structure, 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 P=O moiety is used as a point of saturation between the fluorene bridge and 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 HOMO and LUMO energies of PO6 to be lower by 1.5 eV and 0.59 eV, respectively, compared to a similar diphenylamino substituted derivative. In a simple bilayer OLED device, PO6 exhibits structured UV electroluminescence (EL) at a peak wavelength of 335 nm and structured lower energy emission with peaks at 380 nm and 397 nm, similar to the solid film and crystalline solid photoluminescence spectra. The longer wavelength peaks are attributed to aggregate formation via strong intermolecular interactions (P-O---H-C and edge-to-face C-H---??contacts?) and longer range electrostatic interactions between P=O moieties leading to ordered regions in the film. Devices incorporating PO6 as the host material doped with iridium(III)bis(4,6-(di-fluorophenyl)-pyridinato-N,C2.)picolinate (FIrpic) exhibited sky blue emission with peak external quantum efficiency (?ext,max) of 8.1 % and luminous power efficiency (?p,max) of 25.3 lm/W. At a brightness of 800 cd/m2, generally considered to be sufficient for lighting applications, the ?ext and ?p are 6.7 % and 11.8 lm/W and the operating voltage is 5.6 V, which is significantly lower than has been demonstrated previously using this dopant.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 885197
- Report Number(s):
- PNNL-SA-48238; CMATEX; 830403000; TRN: US200616%%378
- Journal Information:
- Chemistry of Materials, Vol. 18; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
Similar Records
Ultraviolet Electroluminescence and Blue-Green Phosphorescence using an Organic Diphosphine Oxide Charge Transporting Layer.
Inductive effects of diphenylphosphoryl moieties on carbazole host materials: Design rules for blue electrophosphorescent organic light-emitting devices