Designing organic phosphine oxide host materials using heteroarmatic building blocks: inductive effects on electroluminescence
2007
Phosphine oxide substitution of small molecules with high triplet exciton energies allows development of vacuum
sublimable, electron transporting host materials for blue OLEDs. Heteroaromatic building blocks (carbazole,
dibenzofuran and dibenzothiophene) with E T ~ 3 eV were incorporated into phosphine oxide (PO) structures. External
quantum efficiencies (EQEs) at lighting brightness (i.e., 800 cd/m 2 ) reached as high as 9.8% at 5.2V for OLEDs using
the heteroaromatic PO hosts doped with the sky blue phosphor, iridium(III)bis(4,6-(di-fluorophenyl)-pyridinato- N,C 2, )
picolinate (FIrpic). Comparing device properties at a similar current density (i.e., J = 13 mA/cm 2 ) showed the
dibenzothiophene-bridged PO compound exhibits the highest EQEs and lowest operating voltages at all phosphor dopant
levels. These results are explained with respect to the effects of the inductive phosphine oxide substituents on
electrochemical, photophysical and electroluminescence properties of the substituted heteroaromatic building blocks.
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