Synthesis Of The Bipolar Transporting Materials Containing Carbazole And 1,3,4-oxdiazole Units And Study On Their Electroluminescence Properties

The status and history of bipolar-tansporting materials as well as their application in organic/polymer light-emtiing devices (OLEDs/PLEDs) were reviewed in this dissertation. We find that most of the small molecular bipolar-tansporting materials are connected by cojugated group. However, a few of the small molecular bipolar-tansporting materials bridged with non-cojugated group are reported. In order to study the influence of these molecular structures on carrier-transporting and luminescent properties of PLEDs, we designed and synthesized a kind of the small molecular bipolar-tansporting materials containing carbazole and 1, 3, 4–oxadiazole groups bridged with allkyl-idene. The results are listed below.1 A kind of the small molecular bipolar-tansporting materials containing car -bazole and 1, 3, 4–oxadiazole groups bridged with allkyl-idene were obtained. Their stuctures were characterized by 1HNMR and 13CNMR.2 Their melting points (Tm), glass temperature (Tg), decomposition temperature (Td) were characterized by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The bipolar-tansporting materials containing 1,2-ethyl-idene have higher Tm and Tg, but lower Td than those containing of 1, 6-hexyl-idene.3 The UV-vis absorption and photoluminescence properties of these materials in DCM solution and at neat film were studied. All of these materials exhibits intense UV-vis absorption and photoluminescence. Compared with those small molecular bipolar-tansporting materials bridged with cojugated group, these materials display red-shifted emission peak.4 The oxidative and reductive potential, as well as the HOMO and LUMO energy levels were obtained by the cyclic voltammegram (CV). Compared with those small molecular bipolar-tansporting materials bridged with cojugated group, these materials have high HOMO and LUMO energy levels which are close to the corresponding energy levels of polyvinyl carbazole (PVK), but the same energy gap about 3.50 eV. It implys that these materials have stronger hole-transporting ability, weaker electron-transporting ability.5 Using a blend of PVK and PBD or these synthetic bipolar-tansporting materials as host matrix and Firpic as guest, we fabricated the PLEDs. It is found that the devices containing bipolar-transporting materials have lower brightness and higher turn-on voltage than that device containing PBD. The relationship between structure of these bipolar-tansporting materials and device properties were discussed.