Triphenyl phosphine oxide-bridged bipolar host materials for green and red phosphorescent organic light-emitting diodes

Two wide band gap functional compounds of phenylbis(4-(spiro [fluorene-9,9'-xanthen]-2-yl)phenyl) phosphine oxide (2SFOPO) and (4-(9-ethyl-9H- carbazol-3-yl)phenyl)(phenyl)(4-(spiro[fluorene-9,9'-xanthen]-2-y1)phenyl)phosphine oxide (SFOPO-CZ) were designed, synthesized and characterized. Their thermal, photophysical, electrochemical properties and device applications were further investigated to correlate the chemical structure of bipolar host materials with the electroluminescent performance for phosphorescent organic light-emitting diodes (PhOLEDs). Both of them show high thermal stability with glass transition temperatures in a range of 105-122 degrees C and thermal decomposition temperatures at 5% weight loss in a range of 406-494 degrees C. The optical band gaps of compound 2SFOPO and SFOPO-CZ in CH2Cl2 solution are 3.46 and 3.35 eV, and their triplet energy levels are 2.51 eV and 2.52 eV, respectively. The high photoluminescent quantum efficiency of emissive layer of doped green device up to 50% is obtained. Employing the developed materials, efficient green and red PhOLED in simple device configurations have been demonstrated. As a result, the green PhOLEDs of compound SFOPO-CZ doped with tris(2-phenylpyridine) iridium shows electroluminescent performance with a maximum current efficiency (CEmax) of 52.83 cd A(-1), maximum luminance of 34,604 cd/m(2), maximum power efficiency (PE,) of 39.50 lm W-1 and maximum external quantum efficiency (EQE(max)) of 14.1%. The red PhOLED hosted by compound 2SFOPO with bis(2-phenylpyridine)(acetylacetonato) iridium(III) as the guest exhibits a CEmax of 20.99 cd A(-1), maximum luminance of 33,032 cd/m(2), PEmax of 20.72 lm W-1 and EQE(max) of 14.0%. Compound SFOPO-CZ exhibits better green device performance, while compound 2SFOPO shows better red device performance in PhOLEDs. (C)2015 Elsevier B.V. All rights reserved.