Makoto Nagaoka

Benzene substituted with bipyridine and terpyridine as electron-transporting materials for organic light-emitting devices

New electron-transporting materials for organic light-emitting devices (OLEDs) based on trisubstituted benzene with both bipyridine and terpyridine, 1,3-bisbipyridyl-5-terpyridylbenzene (BBTB) and 1-bipyridyl-3,5-bisterpyridylbenzene (BTBB), were developed. Glass transition temperatures of BBTB and BTBB were 93 °C and 108 °C, respectively, and BTBB was completely amorphous with no melting point. Electron mobilities of BTBB exceeded the order of 10−4 cm2 V−1 s−1, while those of BBTB were very high and reached 10−3 cm2 V−1 s−1 at an electric field of approximately 500 kV cm−2. These high mobilities contributed to a low voltage operation. For example, in the case of the conventional aluminum trisquinolinol (Alq)-based fluorescent OLED with BTBB, current densities of 3.5 mA cm−2 and 100 mA cm−2 were reached at voltages of 3.0 V and 4.5 V, respectively. In addition, ionization potentials of BBTB (6.33 eV) and BTBB (6.50 eV) were sufficiently large to confine holes in common emissive layers.