B501819F - View Online PAPER www.rsc.org/materials |...

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High T g blue emitting materials for electroluminescent devices { Jiun Yi Shen, a Chung Ying Lee, ac Tai-Hsiang Huang, a Jiann T. Lin, * ab Yu-Tai Tao, * a Chin-Hsiung Chien a and Chiitang Tsai c Received 5th February 2005, Accepted 27th April 2005 First published as an Advance Article on the web 12th May 2005 DOI: 10.1039/b501819f A series of 2 9 ,7 9 -di- tert -butyl-9,9 9 -spirobifluorene derivatives ( flu ) incorporating arylamines at the 2- and/or 7-positions were synthesized. These compounds possess a high glass transition temperature ranging from 135 to 215 u C. Incorporation of spirobifluorene was found to be beneficial for raising the glass transition temperature ( T g ) of the molecules. Most of the compounds are blue emitting with good solution quantum yields. Blue-emitting double-layer devices with narrow full width at half-maximum (fwhm , 68 nm) were constructed using these materials as the hole-transporting and emitting layer, and TPBI (1,3,5-tris( N -phenylbenzimidazol- 2-yl)benzene) as the electron-transporting layer (device I). In double-layer devices of the configuration ITO/ flu (40 nm)/Alq 3 (40 nm)/Mg : Ag (Alq 3 5 tris(8-hydroxyquinoline)aluminium) (device II), flu functioned mainly as a hole-transporting layer, and the green light characteristic of Alq 3 was detected. Two of the devices of type I have very promising performance, and one of them emits pure blue light (CIE ( x , y ) 5 (0.15, 0.09)). One of the compounds was found to be an efficient hole-injection material. Introduction The pioneering work on small molecule-based and polymer- based organic light-emitting diodes (OLEDs) by Kodak 1 and Holmes’s group 2 respectively, stimulated numerous researchers to jump into this fast-growing area. Following considerable progress in the past decade, more and more products have been commercialized. Low molecular weight small molecules are generally vacuum-deposited as thin films in device fabrication. Therefore, film-forming properties and their temporal stability are prerequisite to the performance and longevity of devices. Amorphous materials possessing high glass transition temperatures ( T g ) should be beneficial for forming glasses and avoiding crystal formation which leads to grain boundary problems. A well known class of amorphous materials is the starburst compounds which have nonplanar molecular structure and exhibit a number of conformations. 3 Another novel class of amorphous materials is the spiro-linked compounds developed by Salbeck’s group. 4 Intramolecular bond rotation and vibration in the spiro-linked unit are not possible and an increase in T g is anticipated. The 9,9 9 -spirobi- fluorene unit appears to be a very promising building block for the construction of high T g blue-emitting materials for high- performance blue electroluminescent devices.
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This note was uploaded on 03/27/2011 for the course CHEM 2211L taught by Professor T.a. during the Spring '08 term at UGA.

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B501819F - View Online PAPER www.rsc.org/materials |...

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