New methods for controlling molecular motion on surfaces

在这个由大分子、超分子和纳米化学项目资助的项目中，塔夫茨大学的查尔斯·赛克斯正在研究如何引导和控制分子在表面上的运动。这种运动以两种方式发生：分子可以以直线或曲线穿过表面，或者它们可以像陀螺一样在适当的位置旋转。目前，人们还不太清楚能量在分子中流动是如何导致它们运动的。这阻碍了新技术的进步。分离或提纯分子的新方法需要控制这两种类型的运动，但这可能很难做到。如果能找到控制这些运动的方法，独特的新应用，包括微型分子大小的泵、传感器、光电子学和组件，可能成为可能。在这项研究中，一种被称为扫描隧道显微镜的复杂成像系统被用来可视化单个分子在表面上的运动。可以对分子施加电脉冲，以便更好地了解能量流如何导致分子运动。这项工作的最终目标是发现有价值的设计原则，用于建造分子机器和分子大小的装置。通过研究人员在当地高中的演讲，这项工作正在产生更广泛的影响。新开发的科学演示、“与科学家相遇”日，以及将高中生纳入研究范围，都将这项工作带给了广泛的受众。更广泛的公众也通过制作YouTube视频来参与这项尖端研究。研究旨在通过解决几个关键问题来开发控制分子旋转和它们在表面上的单向平移的新方法。首先，必须了解分子的内在手性、它的吸附构型和它在表面的势能景观之间的关系。接下来，研究了使货物能够被结合和释放的分子功能。最后，正在研究具有棘齿状能量景观的分子的电激发跳跃，以更好地控制单向运动，为分子在不要求分子具有特定形状/功能的表面上的定向传输提供更一般的方法。虽然这些实验中分子的电子态或振动态是由扫描隧道显微镜尖端的电子激发的，但这种方法可以通过与宏观电子或光源耦合到相同的模式来全局诱导表面上所有分子的定向运动。表面定向分子运动的新微观机制的发现将为可推广到其他系统和领域的原理演示提供重要的证据。这种使能技术对于合理设计用于大规模运输、分离和对映体提纯的新方法至关重要。

In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program, Charles Sykes of Tufts University is investigating ways to direct and control the motion of molecules on surfaces. This motion occurs in two ways: molecules can travel across the surface in straight or curved lines or they can spin in place like a top. Currently, it is not well-understood how energy flowing through molecules causes them to move. This is preventing the advancement of new technologies. New methods for separating or purifying molecules require that these two types of movement be controlled, yet this can be very difficult to do. Unique new applications, including tiny molecular-sized pumps, sensors, optoelectronics, and assemblies, could become possible if a way can be found to control these motions. In this research, a sophisticated imaging system known as a scanning tunneling microscope is being used to visualize the motion of individual molecules on surfaces. Electrical pulses can be applied to the molecules in order to gain a better understanding of how energy flow leads to molecular motion. The ultimate goal of the work is the discovery of valuable design principles for the construction of molecular machines and molecular-sized devices. The work is having a broader impact through presentations the researchers are making at local high schools. Newly developed science demonstrations, "meet a scientist" days, and the inclusion of high school students in the research are bringing the work to a broad audience. The wider public is also engaged in this research through the production of YouTube videos featuring this cutting-edge research.The research is aimed at developing new methods for the controlled rotation of molecules and their unidirectional translation across surfaces by addressing several key questions. First, the relationship between a molecule's intrinsic chirality, its adsorption configuration, and its potential energy landscape on the surface must be understood. Next, molecular functionality that enables cargo to be bound and released is investigated. Finally, the electrically excited hopping of molecules with ratchet-like energy landscapes is being studied to better control unidirectional motion, providing more general approaches to the directional transport of molecules on surfaces that do not require the molecules to be a specific shape/functionality. While the electronic or vibrational states of the molecules in these experiments is to be excited with electrons from a scanning tunneling microscope tip, this method for globally inducing directed motion of all the molecules on a surface is possible by coupling to the same modes either with a macroscopic electron or light source. Discovery of novel microscopic mechanisms for directed molecular motion on surfaces will provide important proof of principle demonstrations that are generalizable in other systems and fields. This type of enabling technology is crucial for the rational design of new approaches for mass transport, separations and enantiopurifications.