Reconfigurable Molecular Crystals through Solid-State Photochemistry

【非技术】生物可以根据环境的变化改变自身结构。在材料研究部固态和材料化学项目的支持下，这项研究的目标是使用人工材料来复制这种类型的反应，这种材料可以根据外部刺激（在这种情况下是光）重新配置自身。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改变。转换后，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的元素是纳米颗粒或胶体，但很明显，最小的可切换元素是分子。发生光化学反应的分子代表一种可转换的元素。由光反应分子组成的晶体在暴露于光后可以自我重组。这个建议是关于分子晶体材料的发展，可以经历光诱导形状变化作为可重构物质的途径。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都有潜在的应用。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。这笔拨款支持的推广工作将改善塔夫脱小学（Taft Elementary）的科学教育，这是一所第一标题（70%的学生处于社会经济劣势）学校，70%的学生是少数族裔。本研究项目有三个主要目标。首先，将开发基于分子晶体的光致运动的新材料和新方法。这种运动通常源于晶体内形成双晶型结构的反应物和生成物分子混合物的存在。新的卤代蒽衍生物将被合成，以提高[4+4]光二聚化反应的稳健性和可逆性。基于二乙烯基蒽衍生物单分子顺反异构化的新型光化学反应也将被探索。材料开发将包括努力开发新的微米级晶体形态，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光力学响应的机制和限制来提高对光力学响应的物理理解。通过测量光强、方向、波长和晶体形状如何影响晶体弯曲的速率和幅度，可以评估不同的理论来解释机械响应。固态核磁共振实验将测量自旋扩散动力学，以评估反应是在整个晶体中均匀进行还是在形成畴时不均匀进行。这些实验将提供在光化学反应中生长的纳米级结构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下后可以自我重塑。表面图案化和微滴印刷将产生由光反应分子组成的分离纳米晶体。这些晶体阵列将用光谱学、扫描探针显微镜和电子显微镜进行表征。光致形状变化将被测量，并与起始晶体形状和大小以及光暴露相关联。

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.