Effect of End Groups on Optoelectronic Properties of Poly(9,9-dioctylfluorene): A Study with Hexadecylfluorenes as Model Polymers
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- 作者：Qilin Wang ; Baohua Zhang ; Lihui Liu ; Yagang Chen ; Yao Qu ; Xiaojie Zhang ; Junwei Yang ; Zhiyuan Xie ; Yanhou Geng ; Lixiang Wang ; Fosong Wang
- 刊名：The Journal of Physical Chemistry C
- 出版年：2012
- 出版时间：October 18, 2012
- 年：2012
- 卷：116
- 期：41
- 页码：21727-21733
- 全文大小：385K
- 年卷期：v.116,no.41(October 18, 2012)
- ISSN：1932-7455
文摘
Monodisperse hexadecyl(9,9-dioctylfluorene)s F16, BrF16, and BF16, which comprise H, Br, and boronic pinacol ester end groups, respectively, were synthesized, and the effect of these end groups on the photophysical, electrochemical, and electroluminescent properties of the polymers were investigated. The end groups have no noticeable effect on the energy levels of the polymers. F16 and BrF16 show high photoluminescence (PL) quantum yields (桅s) in both solution and film states. Film PL 桅s (桅films) of F16 and BrF16 are 0.72 and 0.79, respectively. These values are about 1.4鈥?.5 times of that of BF16 and poly(9,9-dioctylfluorene) (PFO) prepared by Suzuki polycondensation. Moreover, 桅films of F16 and BrF16 were kept almost the same after thermal annealing at 120 掳C in both air and argon atmospheres. By contrast, the 桅films of BF16 and PFO dramatically decreased to 0.25 and 0.29 after thermal annealing at 120 掳C in air. Polymer light-emitting diodes (PLEDs) were fabricated. F16, BrF16, and PFO exhibited maximum luminance efficiencies of 0.60, 0.27, and 0.39 cd路A鈥?, respectively, while that of BF16 was as low as 0.024 cd路A鈥?. Meanwhile, green emission was observed for devices of BrF16, BF16, and PFO, but not for devices of F16. Electron- and hole-only devices were fabricated for elucidating the effect of end groups on charge transporting properties of the polymers. While Br is a mild hole-trapper, boronic ester group traps both holes and electrons, resulting in severely unbalanced hole- and electron-transport. Our results indicate that boronic ester end groups have a detrimental effect on the optoelectronic properties of polyfluorenes larger than Br.