Jacketed Polymers with Dendritic Carbazole Side Groups and Their Applications in Blue Light-Emitting Diodes

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• 作者：Hao Jin ; Yiding Xu ; Zhihao Shen ; Dechun Zou ; Dan Wang ; Wei Zhang ; Xinghe Fan ; Qifeng Zhou
• 刊名：Macromolecules
• 出版年：2010
• 出版时间：October 26, 2010
• 年：2010
• 卷：43
• 期：20
• 页码：8468-8478
• 全文大小：1197K
• 年卷期：v.43,no.20(October 26, 2010)
• ISSN：1520-5835

文摘

Styrene-based monomers with the first- and second-generation dendronized carbazoles were synthesized by a convergent strategy. Conventional free radical polymerizations were carried out to synthesize the dendronized jacketed polymers using these two monomers. The apparent molecular weights of the two polymers determined by gel permeation chromatography were 57000 and 34000 g/mol, respectively. The polymers had excellent thermal stability with their 5% weight loss temperatures all above 360 °C. Their photophysical properties in solutions and films were investigated. Different solvents had negligible effects on their UV−vis or photoluminescent (PL) spectra. A 10 nm blue shift of the emission peak was observed in the PL spectra of films compared with those of solutions. After the films were annealed, the emission peaks became narrower. X-ray diffraction techniques were utilized to examine the phase structures of the dendronized jacketed polymers. The first-generation polymer formed a hexatic columnar nematic phase, while the second-generation one exhibited a columnar nematic phase. This stiff main-chain conformation and the dendritic side-group structure could reduce the intramolecular interactions and aggregations of the carbazole side groups and prevent the formation of excimers, which would be beneficial to the optoelectronic properties. The two polymers showed similar electrochemical properties. Their HOMO levels were about −5.3 eV, which was quite close to that of PEDOT:PSS. Electroluminescent (EL) devices were fabricated in two configurations. A new emission peak was found in the EL spectra compared with the PL spectra. All the devices emitted blue lights and possessed low driving voltages. An introduction of an electron-transporting layer could greatly improve the device properties. The best device could reach a luminescence of 2195 cd/m², a current efficiency of 0.240 cd/A, and an external quantum efficiency of 0.353%.