Reconfigurable Molecular Crystals through Solid-State Photochemistry

生物可以改变其结构，因为它对环境的变化作出反应。 在材料研究部固态和材料化学计划的支持下，这项研究的目标是使用人造材料复制这种类型的响应性，这些材料可以重新配置自己以响应外部刺激，在这种情况下是光。 可重构物质是由更小的元素组成的结构，这些元素的性质可以通过光来切换。 切换后，这些元素可以重新组合成具有不同属性的新复合结构。 该领域的许多工作人员设想可切换元件是纳米颗粒或胶体，但很明显，最小的可切换元件是分子。 经历光化学反应的分子代表可切换元件。 由光反应分子组成的晶体在暴露于光后可以重组自身。 该建议关注的是分子晶体材料的发展，可以经历光诱导的形状变化作为一种途径，以可重构的物质。 在光的作用下发生结构变化的材料在从工程到医学到细胞生物学的广泛学科中具有潜在的应用。 参与的学生将接受光谱学，材料表征和数据分析方面的高级培训。 由这笔赠款支持的外展工作将改善塔夫脱小学的科学教育，这是一所第一类（70%的社会经济弱势）学校，也是70%的少数民族代表不足。 技术摘要本研究计划有三个主要目标。 首先，将开发基于分子晶体的光诱导运动的新材料和方法。 这种运动通常源于晶体内反应物和产物分子的混合物的存在，其形成双压电晶片结构。 新的卤代蒽衍生物将被合成，以提高[4+4]光二聚反应的鲁棒性和可逆性，该反应为晶体机械响应提供动力。 还将探索基于二乙烯基（蒽）衍生物的单分子顺反异构化的新型光化学反应。 材料开发将包括开发新型微米级晶体形态的努力，这些晶体形态可以产生新的机械响应模式。 第二个重点领域将是通过研究其机制和限制来提高对照相机械响应的物理理解。 通过测量光的强度、方向、波长和晶体形状如何影响晶体弯曲的速率和幅度，可以评估解释机械响应的不同理论。 固态核磁共振实验将测量自旋扩散动力学，以评估反应是否在整个晶体中均匀进行或不均匀地形成畴。 这些实验将提供有关在光化学反应过程中生长的纳米级域的大小和形状的信息。 第三，我们将制备纳米晶体阵列，这些纳米晶体在暴露于光后可以重塑自己。 表面图案化之后的微滴印刷将产生由光反应性分子组成的分离的纳米晶体。 这些晶体阵列将通过光学光谱、扫描探针显微镜和电子显微镜来表征。 将测量光诱导的形状变化，并将其与起始晶体形状和尺寸以及光暴露相关联。

Non-technical abstractLiving matter can change its structure as it responds to changes in its environment. With support from the Solid-State and Materials Chemistry program in the Division of Materials Research, the goal of this research is to replicate this type of responsiveness using artificial materials that can reconfigure themselves in response to an external stimulus, in this case light. Reconfigurable matter consists of a structure composed of smaller elements whose properties can be switched by light. After switching, these elements can reassemble into a new composite structure that has different properties. Many workers in the field envision the switchable elements to be nanoparticles or colloids, but it is clear that the smallest switchable element is a molecule. A molecule that undergoes a photochemical reaction represents a switchable element. A crystal composed of photoreactive molecules can then restructure itself after exposure to light. This proposal is concerned with the development of molecular crystal materials that can undergo photoinduced shape changes as a route to reconfigurable matter. Materials that undergo structural changes in response to light have potential applications a wide range of disciplines ranging from engineering to medicine to cell biology. Participating students will receive advanced training in spectroscopy, materials characterization, and data analysis. Outreach efforts supported by this grant will improve science education at Taft Elementary, a Title I (70% socioeconomically disadvantaged) school that is also 70% underrepresented minority. Technical abstractThis research program has three main goals. First, new materials and approaches to molecular crystal-based photoinduced motion will be developed. This motion usually originates from the presence of a mixture of reactant and product molecules within the crystal that form a bimorph structure. New halogenated anthracene derivatives will be synthesized to improve the robustness and reversibility of the [4+4] photodimerization reaction that powers the crystal mechanical response. New types of photochemical reactions based on the unimolecular cis-trans isomerization of divinyl(anthracene) derivatives will also be explored. The materials development will include efforts to develop novel micron-scale crystal morphologies that can give rise to new modes of mechanical response. A second area of focus will be to improve the physical understanding of the photomechanical response by studying its mechanism and limits. By measuring how light intensity, direction, wavelength, and crystal shape affect the rate and magnitude of crystal bending, different theories proposed to explain the mechanical response can be evaluated. Solid-state nuclear magnetic resonance experiments will measure spin diffusion dynamics to assess whether the reactions proceed homogeneously throughout the crystal or heterogeneously with domain formation. These experiments will provide information on both the size and shape of nanoscale domains that grow during the photochemical reaction. Third, we will prepare arrays of nanocrystals that can reshape themselves after exposure to light. Surface patterning followed by microdrop printing will generate separated nanocrystals composed of photoreactive molecules. These crystal arrays will be characterized by optical spectroscopy, scanning probe microscopy, and electron microscopy. Photoinduced shape changes will be measured and correlated with starting crystal shape and size, as well as light exposure.