| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 90 === Abstract
A series of conjugated light emitting materials based on 9,9-spirobifluorene as the core with different terminal substitutents were synthesized by a palladium-catalyzed Suzuki coupling reaction. For improving the electron accepting properties, we introduced pyrimidine into the conjugated backbone as the functional subunits.
Optical properties: The photoluminescence (PL) spectra of F1~F4 in solution lay on blue-light range (392~443 nm), and exhibited good quantum yields. The effective conjugated length of F5 and F6 were shorter than F1~F4, the emission spectra of F5 and F6 were blue-shifted as compared to that of F1~F4. On the other hand, due to the lower symmetry, F5 and F6 performed lower PL efficiency in solution. The nearly identical absorption spectrum in solutions and in films suggests that there are minimal intermolecular interactions in ground state in thin films. These materials also exhibited very high PL quantum yields in thin film, the highest up to 95%. By inspecting the single-crystal X-ray diffraction data of F1 and F2, we found that the rigid structure of spirobifluorene core effectively suppresses intermolecular aggregation. Thermal analysis of these materials reveals high thermal stability with decomposition temperature around 460 oC. The glass-transition temperatures of these materials are higher than 124 oC. We applied F2 as emitter for light emitting diode. Device structure, ITO / PEDT/PSS (300A)/ NCB (450A) / F2 (300A) / Alq3(200A) / LiF / Al, EL lmax = 438（nm), Vturn-on = 4 (V), maximum brightness: 30000 (cd/m2), ΦEL= 2.3 (%). In doping F2 with 1wt.% perylene, the efficiencies had been improved, maximum brightness: 80000 (cd/m2), ΦEL= 4.0 (%).
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