Abstract
In this work, a new series of organic light-emitting materials, derived from dipyrazolopyridine, have been synthesized. The framework of this materials is based on two parts, a dipyrazolopyridine(PAP) unit connected with a triarylamine moiety. The 3, 5 positions of PAP snbstituted with a phenyl or a 4-fluorophenyl group. For the arylamine part, three different substituents, N-phenyl-1-naphthylamino, carbazolyl and dipheylamino groups were used to form the triarylamine moiety. The enhancement of glass transition temperature has been observed on the carbazolyl and N-phenyl-1-naphthylamino group substituted derivatives. The phenyl or 4-fluorophenyl substituents at 3,5 position caused a red shift in the PL spectra. Three-layer devices have been fabricated by using NPB as hole-transporting layer, Alq or TPBI as electron-transporting layer and PAP dyes as light-emitting layer. The structure of device is ITO / NPB(40 nm) / PAP dyes(10 nm) / Alq or TPBI(40 nm) / LiF(1 nm) / Al(150 nm). A series of blue or greenish-blue devices were obtained with high brightness and efficiency. Based on the hole-transporting character of triarylamine, two-layer devices were fabricated by using PAP dyes as hole-electron transporting and light-emitting layer, Alq or TPBI as electron-transporting. With a device configuration of ITO / PAP dyes(40 nm) / Alq or TPBI(40 nm) / LiF(1 nm) / Al(150 nm). The results showed that when Alq was used as electron-transporting material, the recombination region located at the PAP dyes/Alq interface; on the other hand, holes and electrons recombined inside the PAP dyes layer when TPBI was the electron-transporting layer.