Doubly Ortho-Linked Quinoxaline/Diphenylfluorene and cis-Stilbene/Fluorene Hybrids for Optoelectronic Applications

• Main Authors: Wei Yi, 魏屹
• Other Authors: Chen, Chien-Tien
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/89701852972198465392

博士 === 國立臺灣師範大學 === 化學系 === 97 === The development of organic light-emitting diodes (OLEDs) has been investigated because of its widel use in flat-panel display technology in the past two decades. Of all the fluorescent materials, dipolar molecule with charge transporting function in the device was focused in recent years. Moreover, the further bipolar material for single-layered device was newly reported. The applicaions of “quinoxlaine/triphenylamine hydrids” was first reported in our lab in 2005. Furthermore, dipolar “quinoxaline/diphenylfluorene hybrids” as efficiently fluorescence chameleons in OLEDs was then developed by us, too. Based on the concepts, extended molecular design of combining triarylamine units with quinoxaline/ diphenylfluorene backbone leads to yellow-emitting material with comparable electorluminance (EL) efficiencies and makes them become color tuneable in full range. Beside these fluorescent materials, Ir-complexes by using quinoxaline/diphenylfluorene or pyrazine/diphenylfluorene hybrids as cyclomatalating ligands were also investigated as red phosphorescent materials and their devices performance will be examined. On the other hand, the excellent fluorescent quantum yields of stilbene derivatives have been reported but rarely used in OLEDs because of their easy photo-isomerization in nature. One may come up with a new molecule design by linking cis-stilbene moiety with fluorene damper to prevent such undesired behavior. The highly efficient, blue-emitting fluorescence materials were first realized. Moreover, the electron donor/acceptor fragments were combined with the central cis-stilbene core for further applicated to host and dopant materials. On the other hand, some key elements for advanced molecule design of bipolar materials may be consolidated. Finally, those materials developed by ourselves were investigated by using pulse radiolysis (PR) technique. Some relations were shown between their PR results and the features of OLEDs displays after complete examinations. First of all, the experiments for transient absorption studies were carried out. The charge transporting behaviors of one given molecule are used to be measured by its charge mobilities, however, the transient absorption half-lives may provide us another approach to judge these behaviors for dipolar/bipolar molecules. On the other hand, the transient emission profiles for such molecules and their related intensities are also comparable to their EL profiles and efficiencies, respectively. Based on these observations, they are possible to be predicted in advance. Moreover, the EL mechanism after charge recombinations for above materials in OLEDs could be understood by PR studies, too. In the former “quinoxaline/diphenylfluorene hybrids” system, the electron donating properties were effected by the substituents at C5 and C8 positions of each quinoxaline moiety and the processes were then proposed to be different even though these molecules have similar structures. On the other hand, it is supposed to be the same at the later “cis-stilbene/fluorine hybrids” system. In conclusions, we would like to gain some insights to the molecule design for dipoar/bipolar materials in OLEDs. Moreover, it is suggested the use of PR technique in predicting parts of their features in OLEDs in the near future.