Research On Synthesis And Photoelectric Properties Of Organic Phosphorescent Host Materials Derived From Carbazole

In recent years, organic phosphorescence organic light emitting device (PhOLED) has made great progress. PhOLED based on organic phosphorescent materials can capture excited singlet excitons and triplet excitons at the same time, hence, its limited quantum efficiency can achieve100%. In PhOLED, the light-emitting layer was usually composed with organic phosphorescent materials as dopant and phosphorescent materials as host. And, the device performance of PhOLED was usually determined by material performance of phosphorescent host material directly, which generally require broadband gap, high carrier mobility and higher triplet (T1) level.Currently, organic phosphorescent host material is mainly organic small molecule materials which were based on the carbazole derivative. With the N atom containing alone pair of electrons among carbazolyl group, the T1level is higher than that level of the organic phosphorescent light emitting materials. It can transmit effectively three excitons to the organic phosphorescent material to attain its triplet state of the phosphorescent emission.In this work, three kinds of phosphorescent host materials derived from carbazole were designed and synthesized, i. e.9-(6-(9-carbazolyl)hexyl)carbazole(hCP),9-(4-(2-thiophene-based)phenyl) carbazole(sCP) and9-(4-(9-carbazolyl)phenyl)carbazole(pCP). And their structures and properties were characterized:molecular structures were defined by X-ray single crystal diffraction and hydrogen nuclear magnetic resonance (’H NMR). And the optical properties were studied by UV-vis absorption, fluorescence spectra and cyclic voltammetry curve. The PhOLEDs were prepared by using them as host and green-light phosphorescent material tris(2-phenylpyridine)iridium (Ir(ppy)3) as dopant, and the device performances were studied in detail.The experimental results indicated that:(1) hCP molecule possesses strong rigid structure, two carbazole units and alkyl chain of hCP molecule are non-coplanar, which induces in its high triplet energy level (3.01eV) and high glass transition temperature (93℃). Then the PhOLED used hCP as host was fabricated, which exhibited higher maximum current efficiency of15.1cd/A relative to that of the reference PhOLED employed4,4’-bis(N-carbazolyl)-1,1’-biphenyl (CBP) as host, and the maximum current efficiency increased by34.8%.(2)The thienyl unit of sCP plays a strong electronics donating role in formation of asymmetric molecule structer, however, the pCP exhibits planar symmetric molecule structer.(3)The HOMO/LUMO energy levels of sCP and pCP were6.04/2.57and5.95/3.89eV, respectively. The maximum current efficiency of the PhOLED employed sCP as host was35.0cd/A. Compared with the PhOLED used pCP as host, the maximum current efficiency increased by54.9%.