Photoinduced Curling of Organic Molecular Crystal Nanowires
Photoinduced Curling of Organic Molecular Crystal Nanowires
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DOI：
10.1002/anie.201302323
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Bardeen, Christopher J.
中科院分区：
文献类型：
--
作者：
Kim, Taehyung;Al-Muhanna, Muhanna K.;Bardeen, Christopher J.
从基础和技术角度来看，将光转化为机械运动的材料都很有趣。光机械材料通常由组装在有序基质中的光反应分子组成，例如液晶聚合物。[1，2]使用分子晶体作为光机械材料是具有挑战性的，因为反应和未反应的晶相之间的应变经常导致断裂和晶体解体。[3]虽然有宏观晶体的例子可以支持光诱导的形状变化，[4-8]更一般的方法是将S维度的至少一个结构收缩到纳米尺度，以便界面应变可以在表面消散，防止断裂。[9-11]这种小规模的光机械结构可能在细胞生物学等领域有用，但是，生成复杂的动作仍然是一个挑战。在大多数光机械致动器中，定向运动，例如弯曲，是由晶体一侧的照明引起的，从而形成一个由一层反应分子和一层未反应分子组成的双晶片结构。[12]两相之间的界面应变驱动弯曲等定向运动。但是，一旦结构的尺寸低于激发光的衍射极限，只对纳米结构的一侧进行照明就变得不切实际。我们的研究目标之一是开发分子晶体纳米结构，其中定向响应是由晶体形状和分子堆积“内置”的。以前，我们证明了由9-蒽羧酸组成的微带可以在均匀的光照下可逆扭曲，这提供了一个例子，说明了非定向光如何引发复杂的运动。[13]这一运动是由[4+4]蒽环的光二聚作用驱动的，导致了临时的两相(单体和二聚体)系统，其相互作用提供了应变能来扭曲晶体。基于二聚反应的光机械材料并不理想，因为这种双分子反应需要两个分子靠近，这对潜在材料的晶体结构施加了严格的限制。[14]我们最近开始合成菲-9-(1，3-丁二烯)衍生物，目标是开发单分子E！Z可由可见光引发的反应(λ>；430 nm)。一个额外的要求是，由这种分子组成的纳米结构应该能够在均匀的光照条件下执行复杂的运动。我们最近合成了一种新型的9-(1，3-丁二烯)-2-(3-(菲-9-基)烯丙二酸二甲酯)丙二酸二甲酯(DMAAM)。在这里，我们研究了它的固态结构和反应性，并证明了可见光脉冲可以在晶体纳米线中诱导卷曲运动。人们已经投入了大量的努力来制作静态盘绕纳米线，通常是通过改变外部因素，如纳米线S的表面化学或溶剂环境。这项研究中观察到的盘绕在性质上是不同的，因为它依赖于导线本身内部发生的内在化学变化，即E$Z光异构化。这种运动发生在均匀的光照条件下，说明了分子晶体纳米结构在光激发后如何经历不平凡的、可能有用的几何变化。方案1概述了(E)-和(Z)-DMAAM异构体的合成，并在辅助信息中进行了详细说明。这两种分子在室温和黑暗中都是稳定的，可以从各种有机溶剂中结晶。E和Z异构体在…中有重叠吸收光谱
Materials that transform light into mechanical motion are interesting from both fundamental and technological perspectives. Photomechanical materials usually consist of photoreactive molecules assembled in an ordered matrix, for example a liquid crystal polymer.[1, 2] The use of molecular crystals as photomechanical materials is challenging, since strain between reacted and unreacted crystal phases often leads to fracture and crystal disintegration.[3] While there are examples of macroscopic crystals that can support lightinduced shape changes,[4–8] a more general approach is to shrink at least one of the structure s dimensions to the nanometer scale so that interfacial strain can be dissipated at the surface, preventing fracture.[9–11] Such small-scale photomechanical structures could be useful in fields like cell biology, but generating complex motions remains a challenge. In most photomechanical actuators, directional motion, for example, bending, is induced by illumination of one side of the crystal, creating a bimorph structure consisting of a layer of reacted molecules adjacent to a layer of unreacted molecules.[12] The interfacial strain between the two phases drives directional motion like bending. But illuminating only one side of a nanostructure becomes impractical once the size of the structure falls below the diffraction limit of the excitation light.One goal of our research has been to develop molecular crystal nanostructures where the directional response is “built in” by the crystal shape and molecular packing. Previously, we showed that microribbons composed of 9-anthracene carboxylic acid could reversibly twist under uniform illumination, providing an example of how complex motion could be initiated by nondirectional light.[13] This motion was driven by the [4+ 4] photodimerization of the anthracene rings, resulting in a temporary two-phase (monomer and dimer) system whose interaction provided strain energy to twist the crystal. Photomechanical materials based on dimerization reactions are not ideal since this bimolecular reaction requires two molecules to be in close proximity, placing severe constraints on the crystal structure of potential materials.[14] We have recently begun synthesizing anthracene-9-(1, 3-butadiene) derivatives with the goal of developing photomechanical materials powered by a unimolecular E! Z reaction that can be initiated by visible light (λ> 430 nm). An added requirement is that nanostructures composed of this molecule should be able to execute complex motions under uniform illumination conditions. We have recently synthesized a novel anthracene-9-(1, 3-butadiene) derivative, dimethyl-2 (3-(anthracen-9-yl) allylidene) malonate (DMAAM). Here, we study its solid-state structure and reactivity and show that a pulse of visible light can induce a curling motion in crystalline nanowires. Considerable effort has been devoted to making static coiled nanowires,[15–17] usually by changing extrinsic factors like the nanowire s surface chemistry or solvent environment. The coiling observed in this study is qualitatively different, since it relies on intrinsic chemical changes taking place inside the wire itself, namely the E $ Z photoisomerization. This motion occurs under uniform illumination conditions and illustrates how a molecular crystal nanostructure can undergo a nontrivial and possibly useful geometry change after photoexcitation. The synthesis of (E)-and (Z)-DMAAM isomers is outlined in Scheme 1 and described in detail in the Supporting Information. Both molecules are stable at room temperature in the dark and can be crystallized from various organic solvents. The E and Z isomers have overlapping absorption spectra …