| Summary: | 碩士 === 國立交通大學 === 應用化學系 === 90 === A novel fluorene-based oxadiazole-containing polymer (PF-OXD, Part A.) and a series of fluorene derivatives (F-OXDs, Part B.) of high glass-transition temperature was successfully synthesized by introduction of bulky and rigid oxadiazole containing substituents at C-9 position of fluorene units.
In Part A., PF-OXD possesses a very high Tg (213 °C) and very good thermal stability due to its rigid cardo-linkage. In contrast to POF, prolonged heating of PF-OXD thin film (150 °C for 20 h) resulted in no changes in morphology and emissive color. The luminance reaches 2770 cd/m2 at a drive voltage of 10.8 V and the maximum external quantum efficiency is 0.52 % with a bias of 7.4 V. The improved device performance over that of POF may be due to better charge injection and transport from PF-OXD and the efficient energy transfer from OXD side chain to the polyfluorene main chains.
In Part B., those oxadiazole-containing small molecules F-OXDs are able to form stable glasses with higher glass transtion temperatures (128-155 ℃) and better thermal stabilities than 2-(4-diphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). The alternated incorporation of OXD substituents in F-OXDs leads to the tunability of the HOMO/LUMO levels and energy band gaps. Cyclic voltammetry studies reveal that these small molecules possess low-lying LUMO energy levels ranging from 2.46 — 2.84 eV and wide energy band gaps and may be promising candidates as electron-transporting blue hosts.
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