Photophysical and Photomechanical Properties of Molecular Crystal Nanorods

技术总结。 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。 纳米级分子晶体执行器的发展需要了解分子尺度的事件如何联合收割机在晶体纳米结构中产生微米尺度的运动和变形。 此外，还有很大的空间进行材料优化和工具的开发，以控制这些纳米结构的运动。 因此，拟议的研究有两个主要目标：1）确定引起分子晶体纳米棒的光机械响应的物理机制。 将使用各种方法来表征纳米棒在从埃到微米的长度范围内的结构和动力学。 目标是将纳米棒的动态特性（光化学反应速率、晶体变形速率和力产生）与结构特性（棒内的晶体堆积和取向、尺寸和形状以及表面处理）相关联。 这些相关性将导致对分子水平的光化学事件如何引起微观运动的更定量和预测性的理解。2）开发改进的、尺寸可调的纳米级致动器。 材料参数，如可逆性（光诱导和热诱导），和光诱导的体积变化将被优化。 将研究用于选择性控制运动的新光学技术，如双光子激发。 这些结构的实际应用也将开发，重点是两个设备：一个简单的线性致动器的基础上杆膨胀，和一个合成的模拟生物纤毛的基础上可逆的纳米棒弯曲。 改进的物理理解和改进的材料相结合，应该使我们能够评估分子晶体纳米结构作为光机械致动器的最终效用。 在比生物细胞更小的长度尺度上运行的机器可能会导致医学和国防等领域的革命性进步。 但在实现这一目标之前，还有许多问题必须回答，包括如何制造这种结构，如何为它们提供动力，以及如何控制它们的运动。 在拟议的研究中，模板法用于大规模生产有机纳米棒。 当暴露在光下时，这些杆内的分子经历改变其结构的光化学反应。 由于分子在晶体内组织，它们一致移动以使整个纳米结构膨胀或弯曲。 运动的位置和量可以通过激光曝光条件来控制。 以这种方式，光子为这种光机械纳米结构提供了电源和控制机制。 这项提案中的研究将评估这些纳米级机器是否可以用来操纵纳米到微米长度尺度的物体。 此外，基于这项研究的外展计划将用于增加代表性不足的少数民族在科学中的参与。 U.C.滨江是一个西班牙裔服务机构，与周围的初中和高中，超过50%的西班牙裔连接。 允许直接可视化微观现象的实验模块，如布朗运动和纳米棒光力学将被整合到当地学校的课程，以帮助教授加州国家标准的科学教育方面的第七和第八年级。

Technical Summary. Photochemical reactions within molecular crystals provide a way to transform light energy into nanoscale mechanical motion. The development of nanoscale molecular crystal actuators requires knowledge about how molecular-scale events combine to produce micron-scale motions and deformations in crystalline nanostructures. Furthermore, there is much room for material optimization and the development of tools to control the motion of these nanostructures. Thus the proposed research has two main goals:1) To determine the physical mechanisms that give rise to the photomechanical response of molecular crystal nanorods. A variety of methods will be used to characterize the structure and dynamics of the nanorods over a range of lengthscales, from Angstroms to microns. The goal is to correlate the dynamic properties of the nanorods (photochemical reaction rates, crystal deformation rates, and force generation) with structural properties (crystal packing and orientation within the rod, size and shape, and surface treatment). These correlations will result in a more quantitative and predictive understanding of how molecular-level photochemical events give rise to microscopic motions.2) To develop improved, size-tunable nanoscale actuators. Material parameters like reversibility (both light-induced and thermally-induced), and photoinduced volume changes will be optimized. New optical techniques for selective control of motion, like two-photon excitation, will be investigated. Practical applications of these structures will also be developed, with an emphasis on two devices: a simple linear actuator based on rod expansion, and a synthetic analog to biological cilia based on reversible nanorod bending. The combination of improved physical understanding and improved materials should allow us to assess the ultimate utility of molecular crystal nanostructures as photomechanical actuators. Nontechnical SummaryMachines that function on lengthscales 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. In the proposed research, templating methods are used to mass produce organic nanorods. When exposed to light, the molecules within these rods undergo photochemical reactions that change their structure. Because the molecules are organized within a crystal, they move in concert to expand or bend the overall nanostructure. The location and amount of the motion can be controlled by laser exposure conditions. In this way, photons provide both the power source and control mechanism for such photomechanical nanostructures. The research in this proposal will assess whether these nanoscale machines can be used to manipulate objects on nanometer to micron lengthscales. 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 connections to the surrounding middle and high schools that are more than 50% Hispanic. Experimental modules that permit direct visualization of microscopic phenomena like Brownian motion and nanorod photomechanics will be integrated into the curriculum of local schools to help teach aspects of the California State Standards for science education in the 7th and 8th grades.