Fabrication of extended conjugation length polymers within diacetylene monolayers on Au surfaces: Influence of UV exposure time
Fabrication of extended conjugation length polymers within diacetylene monolayers on Au surfaces: Influence of UV exposure time
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DOI：
10.1021/la981219i
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发表时间：
1999-02-16
期刊：
影响因子：
3.9
通讯作者：
Evans, CE
中科院分区：
文献类型：
--
作者：
Cai, M;Mowery, MD;Evans, CE
离域聚合物主链的有效共轭长度是设计用于传感器或非线性光学应用的单层聚合物的关键因素之一。在这份手稿中，光聚合行为的自组装含二乙炔的二硫化物单分子膜上的黄金表面进行评估。使用共振拉曼光谱作为UV暴露时间的函数专门监测聚二乙炔主链结构的长共轭长度（所谓的蓝色形式）的形成。在这些研究中，蓝色聚合物形式的初始形成之后是随着长时间暴露的不可逆损失。这种行为反映了多层Langmuir-Blodgett膜在延长的UV曝光后表现出的向较短共轭长度的色相变。虽然这种相变的确切性质仍然难以捉摸，但大多数理论都集中在影响聚合物主链排列和影响有效共轭长度的因素上。在这里检查三个这样的因素：与表面的Au-S键，烷基侧链的结晶度，和杂交变化引起的应变。当使用还原解吸技术时，Au-S键被示出与聚合过程无关。此外，在聚合后没有观察到链结晶度的变化，但是亚甲基链的扭曲随着长时间的UV暴露而表现出显著的变化。该结果与杂交诱导的应变被翻译到聚合物主链以及亚甲基链中一致，导致有效缀合长度减少。
The effective conjugation length of the delocalized polymer backbone is one of the key factors in designing monolayer polymers for sensor or nonlinear optical applications. In this manuscript, the photopolymerization behavior of self-assembled diacetylene-containing disulfide monolayers is assessed on gold surfaces. Formation of the long conjugation length, so-called blue form, of the polydiacetylene backbone structure is exclusively monitored using resonance Raman spectroscopy as a function of UV exposure time. In these studies, initial formation of the blue polymer form is followed by an irreversible loss with prolonged exposure. This behavior mirrors the chromatic phase transition to shorter conjugation lengths exhibited for multilayer Langmuir-Blodgett films upon extended UV exposure. Although the exact nature of this phase transition remains elusive, most theories focus on factors affecting the alignment of the polymer backbone and influencing the effective conjugation length. Three such factors are examined here: the Au-S bond with the surface, the crystallinity of the alkyl side chains, and the strain induced by hybridization changes. When the reductive desorption technique is used, the Au-S bond is shown to not be correlated with the polymerization process. In addition, no change in chain crystallinity is observed upon polymerization, but the twist of the methylene chain exhibits significant changes with prolonged UV exposure. This result is consistent with the hybridization-induced strain being translated into the polymer backbone as well as the methylene chains, resulting in a decrease in the effective conjugation length.