Preparation and characterization of microscopic photomechanical molecular crystals

分子晶体内的光化学反应提供了一种将光能转化为纳米级机械运动的方法。纳米尺度光刻材料的进步需要跨学科的方法，将材料化学和物理表征结合起来。在这个由固态和材料化学项目支持的联合提案中，巴丁研究小组在分子晶体材料、光谱学和显微镜方面的专业知识将与穆勒研究小组在固态核磁共振（NMR）和计算化学方面的优势相辅相成，以追求一个有两个主要重点的研究项目：1)新的光电材料。我们将集中在热可逆的光刻系统，可以用一个单一的光源操作。为了制造能够在纳米尺度上起作用的照相机械元件，我们将寻找能够在不依赖特殊辐照条件的情况下内在地诱导晶体形状变化的系统。两种新型的光化学“引擎”也将被研究：蒽的单分子杜瓦异构化和热诱导的多晶相变。我们还将开发分子晶体板均匀排列的能力，作为制造基于光电分子晶体的设备的一步。2)固态反应动力学的物理表征及其与晶体变形的关系。该项目的这一部分将涉及使用光学、x射线、核磁共振和计算方法来了解分子级反应如何驱动模型系统中大规模晶体形状的变化。光化学反应开始后，将利用固态核磁共振、x射线衍射和计算方法确定光产物的结构以及反应对晶体堆积的影响。我们还将使用光学和扫描探针显微镜来绘制晶体几何形状作为这些参数的函数是如何变化的。来自这些实验的信息将结合起来，在多个长度尺度和时间尺度上提供照相机械过程的整体图像。在比生物细胞更小的长度尺度上运行的机器可能会在医学和国防等领域带来革命性的进步。但在实现这一目标之前，有许多问题必须得到回答，包括如何生产这种结构，如何为它们提供动力，以及如何控制它们的运动。我们的方法包括在晶体内自组装光化学反应分子，其形状和大小由制备条件控制。由于分子是在晶体内组织的，它们协同移动以扩大或弯曲整个纳米结构。这项提案中的研究将评估这些纳米级光化学“引擎”是否可以用于操纵纳米到微米尺度上的物体。我们还希望对分子水平的化学变化如何结合在一起，在晶体中产生更大的形状变化有一个预测性的理解。此外，基于这项研究的外展计划将用于增加未被充分代表的少数民族在科学领域的参与。加州大学河滨分校是一所西班牙裔服务机构，与周围的公立学校有着密切的联系。我们目前正在为一年级、二年级和四年级班级设计和实施符合加州科学教育标准的拓展模块。与本科生志愿者一起，我们将这些模块带到当地的小学，比如塔夫脱小学，这是一所当地的第一修正案学校，学生中超过50%是西班牙裔。

TECHNICAL SUMMARYPhotochemical reactions within molecular crystals provide a way to transform light energy into nanoscale mechanical motion. Progress in nanoscale photomechanical materials requires an interdisciplinary approach that combines materials chemistry and physical characterization. In this joint proposal, supported by the Solid State and Materials Chemistry program, the Bardeen research group's expertise in molecular crystalline materials, optical spectroscopy and microscopy will be complemented by the Mueller group's strengths in solid-state nuclear magnetic resonance (NMR) and computational chemistry, in order to pursue a research program with two main thrusts:1) New photomechanical materials. We will concentrate on thermally reversible photomechanical systems that can operate with a single light source. To make photomechanical elements that can function on the nanoscale, we will look for systems where changes in the crystal shape can be induced intrinsically without relying on specialized irradiation conditions. Two new types of photochemical "engines" will also be investigated: the unimolecular Dewar isomerization of anthracene, and thermally induced polymorphic phase changes. We will also develop the capability to make uniform arrays of molecular crystal plates as a step toward making devices based on photomechanical molecular crystals.2) Physical characterization of the solid-state reaction dynamics and their connection to crystal deformation. This part of the project will involve using optical, x-ray, NMR and computational methods to understand how molecular-level reactions drive large-scale crystal shape changes in model systems. After the photochemical reaction has been initiated, the structure of the photoproduct and how the reaction affects the crystal packing will be determined using solid-state NMR, x-ray diffraction, and computational methods. We will also use optical and scanning probe microscopy to map out how the crystal geometry changes as a function of these parameters. Information from these experiments will be combined to provide a holistic picture of the photomechanical process on multiple length scales and timescales.NON TECHNICAL SUMMARYMachines that function on length scales smaller than biological cells could lead to revolutionary advances in fields like medicine and defense. But there are many questions that must be answered before this goal can be achieved, including how to produce such structures, how to provide them with power, and how to control their motion. Our approach involves self-assembling photochemically reactive molecules within a crystal, whose shape and size is controlled by the preparation conditions. Because the molecules are organized within a crystal, they move in concert to expand or bend the overall nanostructure. The research in this proposal will assess whether these nanoscale photochemical "engines" can be used to manipulate objects on nanometer to micron length scales. We also want to gain a predictive understanding of how molecular-level chemical changes can combine together to create much larger shape changes in the crystals. In addition, outreach programs based on this research will be used to increase the participation of underrepresented minorities in science. U.C. Riverside is a Hispanic Serving Institution, with strong connections to the surrounding public schools. We are currently designing and implementing outreach modules for 1st, 2nd and 4th grade classes that are consistent with the California State Standards for science education. With undergraduate volunteers, we are bringing these modules to local elementary schools, like Taft Elementary, a local Title I school whose student body is more than 50% Hispanic.