结晶学
芴
透射电子显微镜
结晶
亚稳态
吸收(声学)
吸收光谱法
化学
相(物质)
吸收边
材料科学
谱线
分析化学(期刊)
聚合物
光学
带隙
有机化学
纳米技术
物理
天文
光电子学
复合材料
作者
S. H. Chen,and A. C. Su,Chun‐Jen Su,S. A. Chen
出处
期刊:Macromolecules
[American Chemical Society]
日期:2004-12-21
卷期号:38 (2): 379-385
被引量:214
摘要
By means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) we demonstrate the presence of a previously unspecified modification (α‘) of the crystalline (α) phase in poly(9,9-di-n-octyl-2,7-fluorene) (PFO). The α‘ form is metastable and lower in melting temperature than the α form, and its formation is kinetically favored at temperatures lower than 130 °C. The modification involves mainly a slight increase in the b axis from 2.34 to 2.38 nm and lowered symmetry along this axis, whereas the a axis tends to lie preferentially normal to film surface. Using specimens composed selectively of α and α‘ phases, respectively, we show that films of the two forms are characteristically different in routine 1-D XRD profiles and absorption spectra. These are attributable to the oriented nature of the α‘ form as well as minor but significant differences in molecular packing and backbone coplanarity. However, photoexcited emission spectra of these films remain highly similar in the vibronic structure to the purely nematic film, with only minute shifts in emission maxima that are inconsistent with the significantly red-shifted absorption edge upon crystallization. This appears better explained by assuming that the liquid-crystalline matrix rather than crystalline domains dominates optical emission of PFO.
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