cm0600677_si_002.cif (19.73 kB)
New Charge Transporting Host Material for Short Wavelength Organic Electrophosphorescence: 2,7-Bis(diphenylphosphine oxide)-9,9-dimethylfluorene
dataset
posted on 2006-05-02, 00:00 authored by Asanga B. Padmaperuma, Linda S. Sapochak, Paul E. BurrowsWe 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 solid film
and crystalline solid photoluminescence spectra. The longer wavelength peaks are attributed to aggregate
formation via strong intermolecular interactions (PO···HC and edge-to-face CH···π contacts) and
longer range electrostatic interactions between PO moieties leading to ordered regions in the film.
Devices incorporating PO6 as the host material doped with iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2)picolinate (FIrpic) exhibited sky blue emission with peak external quantum efficiency (ηext,max) of
8.1% and luminous power efficiency (ηp,max) of 25.1 lm/W. At a brightness of 800 cd/m2, generally
considered to be sufficient for lighting applications, the ηext and ηp 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.