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·赛克斯正在研究指导和控制表面分子运动的方法。这种运动以两种方式发生：分子可以沿着直线或曲线在表面上移动，或者它们可以像陀螺一样在原地旋转。目前，人们还不太清楚流经分子的能量是如何使它们运动的。这阻碍了新技术的发展。分离或纯化分子的新方法需要控制这两种类型的运动，但这很难做到。如果能找到控制这些运动的方法，包括微小分子大小的泵、传感器、光电子和组件在内的独特新应用将成为可能。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表面上单个分子的运动。电脉冲可以应用于分子，以便更好地理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，用于构建分子机器和分子大小的设备。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，“与科学家见面”日，以及将高中生纳入研究，将这项工作带给了广泛的受众。更广泛的公众也通过制作展示这一前沿研究的YouTube视频参与了这项研究。该研究旨在通过解决几个关键问题，开发分子控制旋转及其在表面上的单向平移的新方法。首先，必须了解分子的固有手性、吸附构型和表面势能之间的关系。接下来，分子功能，使货物被绑定和释放进行了研究。最后，正在研究具有棘轮状能量景观的分子的电激发跳跃，以更好地控制单向运动，为分子在表面上的定向运输提供更通用的方法，而不需要分子具有特定的形状/功能。虽然这些实验中分子的电子或振动状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。分子在表面上定向运动的新微观机制的发现，将为在其他系统和领域推广的原理论证提供重要的证明。这种类型的使能技术对于合理设计大规模运输，分离和对映纯化的新方法至关重要。

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.