Takahashi Masashi, Okuhara Takashi, Yokohari Tomohiro, Kobayashi Koichi
Department of Environmental Energy Engineering, Musashi Institute of Technology, 1-28-1 Tamazutsumi, Setagaya, Tokyo 158-8557, Japan.
J Colloid Interface Sci. 2006 Apr 1;296(1):212-9. doi: 10.1016/j.jcis.2005.09.007. Epub 2005 Sep 26.
Photoactive film material of long-chain azobenzene derivative, p-(omega-trimethylammoniodecyloxy)-p'-octyloxyazobenzene bromide (TAOAB), was fabricated into a Langmuir-Blodgett (LB) film by a polyion-complex technique using poly(sodium 4-styrenesulfonate) as a polyanion. To investigate the effect of the packing state of the azobenzene chromophore on its orientation and cis-trans isomerization, TAOAB was mixed with methyl stearate in the LB film matrix at various mole fractions (X(TAOAB)), and structural characterizations were subsequently carried out by means of Fourier transform infrared and ultraviolet-visible spectroscopies, X-ray diffraction analysis, and atomic force microscopy. The results obtained show that as the degree of packing increases, both the azobenzene chromophores and the hydrocarbon chains orient more perpendicularly to the surface of the LB film. In addition, reversible cis-trans photoisomerization of TAOAB took place upon alternate irradiation with UV and visible light even in a mixed LB film with the chromophores in a dense lateral packing state. In the process of thermal cis-to-trans isomerization, we found that the reaction rate is strongly affected by the packing state of TAOAB at 20 degrees C, reflecting the differences in steric hindrance among LB films of various X(TAOAB). In addition, higher activation energy was obtained for thermal cis-to-trans isomerization when the free volume around the chromophores became smaller.
通过使用聚（4-苯乙烯磺酸钠）作为聚阴离子的聚离子复合技术，将长链偶氮苯衍生物对-（ω-三甲基铵癸氧基）-对'-辛氧基偶氮苯溴化物（TAOAB）的光活性薄膜材料制成朗缪尔-布洛杰特（LB）膜。为了研究偶氮苯发色团的堆积状态对其取向和顺反异构化的影响，在LB膜基质中以不同的摩尔分数（X(TAOAB)）将TAOAB与硬脂酸甲酯混合，随后通过傅里叶变换红外光谱和紫外-可见光谱、X射线衍射分析以及原子力显微镜进行结构表征。所得结果表明，随着堆积程度的增加，偶氮苯发色团和烃链都更垂直于LB膜表面取向。此外，即使在发色团处于密集横向堆积状态的混合LB膜中，用紫外光和可见光交替照射时，TAOAB也会发生可逆的顺反光异构化。在热顺-反异构化过程中，我们发现在20℃时反应速率受TAOAB堆积状态的强烈影响，这反映了不同X(TAOAB)的LB膜之间空间位阻的差异。此外，当发色团周围的自由体积变小时，热顺-反异构化获得了更高的活化能。
