High Tg blue emitting materials for electroluminescent devices

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Abstract
A series of 2′,7′-di-tert-butyl-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 °C. Incorporation of spirobifluorene was found to be beneficial for raising the glass transition temperature (Tg) 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)/Alq3 (40 nm)/Mg : Ag (Alq3 = tris(8-hydroxyquinoline)aluminium) (device II), flu functioned mainly as a hole-transporting layer, and the green light characteristic of Alq3 was detected. Two of the devices of type I have very promising performance, and one of them emits pure blue light (CIE (x,y) = (0.15, 0.09)). One of the compounds was found to be an efficient hole-injection material.