New Charge Transporting Host Material for Short Wavelength Organic Electrophosphorescence: 2,7-Bis(diphenylphosphine oxide)-9,9-dimethylfluorene
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- 作者：Asanga B. Padmaperuma ; Linda S. Sapochak ; and Paul E. Burrows
- 刊名：Chemistry of Materials
- 出版年：2006
- 出版时间：May 2, 2006
- 年：2006
- 卷：18
- 期：9
- 页码：2389 - 2396
- 全文大小：263K
- 年卷期：v.18,no.9(May 2, 2006)
- ISSN：1520-5002
文摘
We report the synthesis, crystal structure, and photophysical and electroluminescent properties of anew 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 isused as a point of saturation between the fluorene bridge and the outer phenyl groups so that the tripletexciton energy of PO6 is 2.72 eV, similar to that of a dibromo substituted fluorene, but it is more amenableto 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 PO6to 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 wavelengthof 335 nm and structured lower energy emission with peaks at 380 and 397 nm, similar to the solid filmand crystalline solid photoluminescence spectra. The longer wavelength peaks are attributed to aggregateformation via strong intermolecular interactions (P-O···H-C and edge-to-face C-H···
es/gifchars/pi.gif" BORDER=0 > contacts) andlonger 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-(difluorophenyl)pyridinato-N,C2)picolinate (FIrpic) exhibited sky blue emission with peak external quantum efficiency (es/gifchars/eta.gif" BORDER=0 >ext,max) of8.1% and luminous power efficiency (es/gifchars/eta.gif" BORDER=0 >p,max) of 25.1 lm/W. At a brightness of 800 cd/m2, generallyconsidered to be sufficient for lighting applications, the es/gifchars/eta.gif" BORDER=0 >ext and es/gifchars/eta.gif" BORDER=0 >p are 6.7% and 11.8 lm/W and theoperating voltage is 5.6 V, which is significantly lower than has been demonstrated previously using thisdopant.