Synthesis And Application In OLED Of Imidazole/Carbazole Hybrid Bipolar Deep Blue Material

Much reseach has been carried out on organic light-emitting diode in both academic and industrial fields for the past decades,due to its enormous and promising potential applications full color display and solid-state lighting.Although much progress took place,blue emitters' performance,stability,color purity were still inferior compared with successful red and green counterpartsIn this thesis,six bipolar deep blue emitting materials incorporating carbazole as a mild electron donor and imidazole as an electron acceptor with twisted biphenyl as a ? bridge were successfully synthesized.Nuclear magnetic resonance and mass spectrum were carried out to characterize the target molecual structure,and X-ray crystallography was collected to identify two single-crystal structure.Thermal,photophysical properties and target molecular levels were studied comprehensively.Combined with theory calculate and single-crystal data,the structure-performance relationship was explored.The photo-fluorescent spectra of target moleculars both in solution and film state showed deep blue emission,especially for imidazole derivatives.The solution fluorescent quantum yield was measured with 0.01 M quinine sulfate as a reference standard are in the range of 83.3~ 92.5%.Small red shift emission indicated twisted structure can contribute to suppress the strong aggregation in the film state.Negligible solvent effect demonstrated introducing weaker electron donor and twisted molecular could restrain the intramolecular charge transfer function effectively.The highest occupied molecular orbital energy levels were determined by Photo-electron Yields Spectroscopy to be-5.87~-5.56 eV matched well with N,N'-Bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1'-biphenyl)-4,4'-diamine's highest occupied molecular orbital level.Target compounds possessed good thermal stabability with high decomposition temperature(Td,> 351°C)and glass transition temperature(Tg,> 134°C).Spin-coated and vacuum deposited film were smoothy and amorphous before and after 24 h 90° annualing process exhibited good film stability which demonstrated that both spin-coated and vacuum deposited process were suitable for target molecular to manufacture the OLED devices.Single-carrier devices performance of 9-(4'-(1,4,5-triphenyl-1H-imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-9H-carbazole proved to be its good bipolar transporting characteristics.The non-doped fluorescent organic light-emitting diode based on 2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-1-(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazole and 9-(4'-(1,4,5-triphenyl-1H-imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-9H-carbazole(device A and B respectively)exhibited deep blue emission with maximal EL peak at 440 nm and 420 nm respectively,CIE coordinate was(0.154,0.072)and(0.166,0.064)at 9 V driving voltage approaching EBU blue standard.With increasing driving voltage,EL spectra and CIE coordinate changed slightly,suggesting a relatively stable EL emission.The devices showed excellent EL performance with maximal current efficiency of 2.23 cd/A and 2.30 cd/A respectively,maximal power efficiency of 0.81 lm/W and 1.52 lm/W respectively,the later was almost best among deep blue devices with CIEy ? 0.064.