Spectroscopic Ellipsometry and Fluorescence Study of Thermochromism in an Ultrathin Poly(diacetylene) Film: Reversibility and Transition Kinetics
Spectroscopic Ellipsometry and Fluorescence Study of Thermochromism in an Ultrathin Poly(diacetylene) Film: Reversibility and Transition Kinetics
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DOI：
10.1021/la991580k
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发表时间：
2000-01
期刊：
影响因子：
3.9
通讯作者：
R. Carpick;T. Mayer;D. Sasaki;A. R. Burns
中科院分区：
文献类型：
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作者：
R. Carpick;T. Mayer;D. Sasaki;A. R. Burns
我们研究了超薄聚二乙炔薄膜的热致变色转变。该Langmuir薄膜由3层聚合的10，12-十五碳二元酸[CH{sub3}(CH{sub2}){sub11}C{Triple_ond}CC{Triple_ond}C(CH{sub2}){sub8}COOH](聚PCDA)组成，在硅衬底上排列成晶区。通过现场温度控制，获得了椭圆偏振光谱和荧光强度测量结果。Poly-PCDA薄膜表现出从最初的蓝色到仅在高温下(303-333K)存在的中间“紫色”形式之间的可逆热转变，然后在320K以上热处理后发生不可逆的向红色形式的转变。我们认为紫色形式是热变形的蓝色聚PCDA，可能代表了不可逆转变为红色的过渡构型。根据椭圆偏振测量法的测量，每种形式的吸收光谱中都出现了独特的特征，这支持了这一假说。显著的荧光发射只发生在红色形式，并在温度升高时减少，而吸收保持不变。排放的减少可能与碳氢侧链的热波动有关。进行了不可逆转变的时间分辨荧光测量。通过对这些测量结果的一级动力学分析，我们推导出蓝光和红光之间的势垒为17.6+-1.1kcal molsup-1。
We have investigated the thermochromic transition of an ultrathin poly(diacetylene) film. The Langmuir film is composed of three layers of polymerized 10,12-pentacosadiynoic acid [CH{sub 3}(CH{sub 2}){sub 11}C{triple_bond}CC{triple_bond}C(CH{sub 2}){sub 8}COOH] (poly-PCDA) organized into crystalline domains on a silicon substrate. Spectroscopic ellipsometry and fluorescence intensity measurements are obtained with in-situ temperature control. Poly-PCDA films exhibit a reversible thermal transition between the initial blue form and an intermediate ''purple'' form that exists only at elevated temperature (between 303-333 K), followed by an irreversible transition to the red form after annealing above 320 K. We propose that the purple form is thermally distorted blue poly-PCDA, and may represent a transitional configuration in the irreversible conversion to red. This hypothesis is supported by the appearance of unique features in the absorption spectra for each form as derived from the ellipsometry measurements. Significant fluorescence emission occurs only with the red form, and is reduced at elevated temperatures while the absorption remains unchanged. Reduced emission is likely related to thermal fluctuations of the hydrocarbon side chains. Time-resolved fluorescence measurements of the irreversible transition have been performed. Using a first-order kinetic analysis of these measurements we deduce an energy barrier of 17.6 {+-} 1.1 kcal mol{sup -1} between the blue and red forms.