Thermodriven chiroptical switching of a polysilane thin film
Thermodriven chiroptical switching of a polysilane thin film
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DOI：
10.1021/ma049807s
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发表时间：
2004-04
期刊：
影响因子：
5.5
通讯作者：
Sunyoung Kim;M. Fujiki;A. Ohira;and Giseop Kwak;Y. Kawakami
中科院分区：
文献类型：
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作者：
Sunyoung Kim;M. Fujiki;A. Ohira;and Giseop Kwak;Y. Kawakami
在分子水平上设计和开发用于手光开关和存储器的智能材料是材料科学与工程中小型化的一个具有挑战性的问题。[1]开关系统的基本要求是分子的双稳态，它可以通过外部刺激快速相互转换。2在许多含有对映体纯手性侧链的合成聚合物（例如，多异氰酸酯，3聚乙炔，4聚噻吩，5聚芴，6和聚硅烷7）中，它们的主链采用优先螺旋方向，P（正，右手）或M（负，左手）。这种聚合物是作为分子手性开关的有希望的候选者，因为它们的可逆的双稳态，其可以通过螺旋-螺旋转变被分配为“+1和-1”或通过螺旋-卷曲转变被分配为“+1和0”。圆二色性（CD）可以在高分子链的吸收区检测到高分子的构象变化。虽然已经建立了许多关于溶液中螺旋构象转换的研究，但它们可能是初步的。从实用的角度来看，无论是在散装薄膜或聚合物基体中的转变的重点是必要的。8玻璃化转变温度（Tg）是固态手形光开关设计中的关键因素。低于Tg时，聚合物链的链段运动被冻结。即使高于Tg，响应时间也将取决于Tg和构象转变温度（Tc）之间的差。因此，具有相对低的Tg的聚合物可以是实际应用的良好候选物。聚硅烷在300 ~ 400 nm的紫外区具有独特的电子吸收带，这是由于离域电子沿着硅骨架的σ-σ* 电子跃迁。9聚硅烷的构象强烈依赖于取代基种类，紫外吸收中λmax的位置反映了它们与共轭程度有关的构象。特别是，在具有对映体纯手性侧链的聚硅烷中，它们的螺旋方向可以通过库恩不对称比（gabs）Δ λ/λ表征，因为CD光谱通常显示出与UV吸收带相似的轮廓，并且gabs的值给出了与优先螺旋方向的程度相关的定量信息。因此，具有相关对映体纯手性侧链的聚硅烷将是分子水平上手性光学开关和记忆的成功候选者。在这项工作中，我们报告了聚{（S）-3，7-二甲基辛基-正丙基硅烷}（PDMOPS）在溶液和固态中的螺旋-卷曲转变，以及其作为手握光学开关和存储器应用的可行性。
The design and development of smart materials for a chiroptical switch and memory at the molecular level is a challenging issue for miniaturization in materials science and engineering. 1 The basic requirement for a switching system is the bistable states of a molecule, which can be rapidly interconverted by an external stimulus. 2 In many synthetic polymers containing enantiopure chiral side chains (eg, polyisocyanates, 3 polyacetylenes, 4 polythiophenes, 5 polyfluorenes, 6 and polysilanes7), their backbone adopts a preferential screw sense, P (plus, right-handed) or M (minus, left-handed). Such polymers are promising candidates as molecular chiroptical switches because of their reversible bistable states, which can be assigned as either “+ 1 and-1” through the helix-helix transition or “+ 1 and 0” through the helix-coil transition. The conformational change of polymers can be detected in the absorption region of the polymer chains by circular dichroism (CD). Although many studies have been established concerning the switching of the helical conformation in solution, they might be preliminary. A focus on the transition, either in bulk thin film or in a polymer matrix, is needed from a practical viewpoint. 8 The glass transition temperature (Tg) is the critical factor in the design of the chiroptical switch in the solid state. Below Tg, the segmental motion of the polymer chain is frozen. Even above Tg, the response time would depend on the difference between Tg and the conformational transition temperature (Tc). Thus, the polymer having a relatively low Tg may be a good candidate for practical application. Polysilanes exhibit a unique electronic absorption band in the UV region ranging from 300 to 400 nm, which is assigned to the σ-σ* electronic transition of the delocalized electrons along the silicon backbone. 9 The conformation of polysilanes strongly depends on the substituent species, and the position of λmax in the UV absorption reflects their conformation in connection with the degree of conjugation. Especially, in polysilanes having enantiopure chiral side chains, their helical sense can be characterized by the Kuhn dissymmetry ratio (gabs), Δϵ/ϵ, because the CD spectra generally show a similar profile to the UV absorption band, and the value of gabs gives the quantitative information associated with the degree of a preferential screw sense. 10Polysilanes possessing relevant enantiopure chiral side chains will, therefore, be successful candidates for a chiroptical switch and memory at the molecular level. In this work, we report on the helix-coil transition of poly {(S)-3, 7-dimethyloctyl-n-propylsilane}, PDMOPS, in solution as well as in the solid state and on the feasibility of its application as chiroptical switches and memory.