Single molecule electric motors

虽然宏观电机对具有定向运动的定向驱动力做出反应，但热能冲刷纳米级任何机器中的状态种群，导致布朗运动。除了在生物系统中发现的各种各样的分子机器之外，人工设计的分子马达仍然很少见。我们打算利用电流的自旋角动量来建立新的驱动纳米级器件的驱动力。几年前，Ono等人提出了自旋转移力矩电机的想法，其中自旋极化电流通过分子中的自旋翻转散射而去极化，从而产生力矩。然而，这一概念仍有待实验验证。我们的项目旨在合成合适的分子复合物并通过实验测试这一概念。为了将这一概念扩展到未极化的注入电流，在第二次尝试中，我们将利用轴向手性分子的自旋选择性传输，使得电流在分子内极化，也导致扭矩。我们的第三种方法依赖于一个更经典的原理，使用磁场中通过分子的电流的洛伦兹力。在本项目中，我们计划通过合成螺旋手性多环芳烃体系来构建自旋驱动的分子马达，该体系包括三脚架平台，基于我们对类似分子三脚架结构的实验经验和我们在螺旋手性分子合成方面的专业知识，我们将合成具有指定旋转轴的三脚架平台的合适组合，该三脚架平台包括重金属络合物或不同的手性多环芳烃头部基团。在这里，我们依靠我们在合成单个分子构建模块方面的成熟专业知识。低温扫描隧道显微镜（LT STM）允许精确地接近单个分子，甚至以受控的方式寻址分子的特定部分。我们已经表明，在初步的工作中，使用STM，一个单一的分子的手性和它的旋转方向可以确定。由于我们的STM的工作温度为5 K，等于半meV范围内的热能，亚稳系统的统计布居态的能量可以精确地确定到几μeV的范围。转子或隧道参数的微小化学修饰预计将反映在旋转行为和不同状态的种群中。工作的单向分子马达将作为进一步研究的起点，旨在详细了解螺旋手性复合物中的自旋弛豫过程。合成化学和实验表面科学之间的密切合作建立在每周快速反馈的基础上，将使我们能够广泛地测试所提出的概念，并确定合适的分子脚和功能性头部基团的组合。

While macroscopic motors react to a directed driving force with a directed motion, thermal energy washes over state population in any machines at the nanoscale resulting in brownian motion. Besides the astonishing variety of molecular machines found in biological systems, artificially designed molecular motors are still rare. We intend to establish new driving forces for actuating nanoscale devices exploiting the spin angular momentum of an electric current. The idea of a spin-transfer torque motor, in which a spin-polarized current is depolarized by spin flip scattering in a molecule creating a torque was proposed some years ago by Ono et al. However, this concept is still to be experimentally verified. Our project aims to synthesize suitable molecular complexes and to experimentally test this concept. In order to extent this concept to injected currents that are unpolarized, in a second attempt, we will exploit the spin-selective transmission of axial chiral molecules such that a current is polarized within the molecule also leading to a torque. Our third approach relies on a more classical principle using the Lorentz force of the current through the molecule in a magnetic field. In the present project, we plan to built spin-driven molecular motors by synthesizing helical chiral poly-aromatic systems that comprise tripodal platforms building on our experimental experience with similar molecular tripodal structures and our expertise in the synthesis of helical chiral molecules.We will synthesize suitable combinations of tripodal platforms with a designated rotation axis comprising heavy-metal complexes or different chiral poly-aromatic head groups. Here, we rely on our proven expertise in the synthesis of the individual molecular building blocks. Low temperature scanning tunneling microscopy (LT STM) allows to accurately approach single molecules and even to address specific parts of a molecule in a controlled way. We have shown in preliminary work that using STM, the chirality of a single molecule and its rotation direction can be identified. As the working temperature of our STM of 5 K is equal to thermal energies in the range of half an meV, energies of statistically populated states of a metastable system can be determined precisely down to the range of few μeV. Minor chemical modifications of the rotor or the tunneling parameters are expected to be reflected in the rotational behavior and the population of the different states. A working unidirectional molecular motor will serve as starting point for further investigations that aim at a detailed understanding of the process of spin relaxation in helical chiral complexes. A close collaboration between the synthetic chemistry and experimental surface science building on fast feedback on a weekly basis will enable us to extensively test the proposed concepts and to identify suitable combinations of molecular feet and functional head groups.