Single molecule electric motors

当宏观马达通过定向运动对定向驱动力作出反应时，热能在纳米尺度的任何机器中冲刷状态布居，导致布朗运动。除了生物系统中发现的种类惊人的分子机器外，人工设计的分子马达仍然很少见。我们打算建立新的驱动力，利用电流的自旋角动量来驱动纳米设备。几年前，小野等人提出了自旋转移力矩马达的想法，即通过分子中的自旋反转散射来去极化自旋极化的电流，从而产生扭矩。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络合物，并对这一概念进行实验验证。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，使分子内的电流极化也导致扭矩。我们的第三种方法依赖于一个更经典的原理，利用磁场中通过分子的电流的洛伦兹力。在目前的项目中，我们计划通过合成螺旋手性多芳香族体系来构建自旋驱动的分子马达，这些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合成螺旋手性分子方面的专业知识，我们将合成具有指定旋转轴的合适的三脚架平台组合，包括重金属络合物或不同的手性多芳香族头基。在这里，我们依靠我们在单个分子构建块合成方面的成熟专业知识。低温扫描隧道显微镜(LT STM)可以精确地接近单个分子，甚至以可控的方式定位分子的特定部分。我们已经在初步工作中表明，使用扫描隧道显微镜可以识别单个分子的手性及其旋转方向。由于我们的扫描隧道显微镜的工作温度为5K，相当于半meV范围内的热能，因此可以精确地确定亚稳态系统统计布居态的能量，精确到极小的μeV范围。对转子或隧穿参数的微小化学修改有望反映在旋转行为和不同状态的布居中。一个工作的单向分子马达将作为进一步研究的起点，目的是详细了解螺旋手性络合物的自旋弛豫过程。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，将使我们能够广泛测试所提出的概念，并确定合适的分子脚和功能头基团的组合。

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.