| Since the groundbreaking work on organic light-emitting diodes(OLEDs) by the Kodak Company and Cambridge University, OLEDs have caused considerable industrial and scientific attention due to their applications in flat-panel displays and solid-state lighting, which could be the next generation flat panel display technology. The light-emitting materials are important components of OLEDs. Howere, the performance of the blue light-emitting materials should be further improved compared with that of green and red light-emitting materials. At present, the blue light-emitting materials have some problems such as color purity and carrier transport imbalance.In this dissertation, three novel electroluminescent materials containing hole-transporting 3, 6- di- tert- butyl- carbazole as a donor(D) and electron-transporting s-triazine as an acceptor(A) were successfully synthesized, which were 9, 9', 9"-(1, 3, 5- triazine- 2, 4, 6- triyl) tris(3, 6- di- tert-butylcarbazole)(TazTCz), 9, 9'-(6- phenyl- 1, 3, 5- triazine- 2, 4- diyl) bis(3, 6- di-tert- butyl- carbazole)(PhTazDCz) and 9-(4, 6- diphenyl- 1, 3, 5- triazine- 2- yl)- 3, 6- di- tert- butyl-carbazole(DPhTazCz). The effect of different D/A ratio on photoelectric properties was discussed with quantum chemistry calculations. The bipolar transporting properties of compounds were realized through the introduction of donor and acceptor. Moreover, the small molecular film forming ability was improved and the fields of application was also broadened. All the compounds were characterized by proton nuclear magnetic resonance(1H NMR), carbon nuclear magnetic resonance(13C NMR) and mass spectrum(MS) technologies.The optical, electrochemical, thermal properties and carrier mobilities were investigated comprehensively. The structure-property relationship of the compounds was studied combining quantum chemistry calculations. It indicates that the overall planarity of molecule and conjugation degree can be increased with increasing the number of phenyl attached on the s-triazine, resulting in the red-shifted emission peaks and the improvement of the fluorescence quantum yield. All compounds represented solvent influence, which are consistent with Lippert-Mataga equation. The triplet state energy levels are 2.84 ~ 2.86 eV for these compounds, which could be used as host materials in blue PHOLEDs. These compounds possess high decomposition temperature Td(341 ~ 462 °C). The HOMO levels of as-synthesized compounds are roughly the same at-5.89 ~-5.85 eV, while the optical bandgaps are in the range of 3.05 ~ 3.47 eV. At room temperature, the hole mobilities are between 1.04×10-6 cm2 V-1 s-1 and 1.20×10-5 cm2 V-1 s-1. While, the electron mobilities are in the range of 1.46×10-6 ~ 5.83×10-6 cm2 V-1 s-1. The compounds exhibit bipolar transporting properties with increasing the number of phenyl attached on the s-triazine.The amorphous, surface properties of organic thin films fabricated with spin-coating were also investigated. The film formability of these compounds could be improved by increasing the number of tert-butyl group. X-ray single crystal structural analysis revealed a twisted “propeller-shaped” structure of TazTCz, which prevented the intermolecular close-packing in the solid state and formed amorphous thin films.The PHOLEDs were fabricated with TazTCz, PhTazDCz and DPhTazCz as host materials and Iridium(III) bis [(4, 6- di- fluorophenyl)- pyridinato- N, C2'] picolinate(FIrpic) as the blue-emitting phosphor. The PHOLEDs with PhTaz DCz and DPhTazCz as hosts showed slight “efficiency roll-off” due to the balanced carrier mobilities. The non-doped fluorescent device fabricated by spin-coating method with TazTCz as light-emitting material revealed CIE(0.16, 0.08), which was close to the NTSC standard blue coordinates(0.14, 0.08). |
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