Design, Synthesis, Crystallization and Materials Properties of Rotary Dipolar Arrays

非技术总结：在美国国家科学基金会材料研究部的支持下，这项研究旨在开发一种新型材料，称为双动力晶体，它具有基于其组成分子中包含的基团的重定向和旋转运动的可切换物理性质。这些晶体分子转子具有精心挑选的电、磁和光学特性，将能够对外部场做出反应，并改变材料的物理特性。为这个项目提出的结构可以被看作是一个有序的罗盘阵列，每个罗盘针都被固定在一个盒子里，它能够影响它最近的邻居的方向。因为每个旋转的针都有正极和负极，所以每个针都被称为“偶极子”。据预测，一些特定的分子罗盘排列将导致所有的偶极子指向同一个方向，而另一些将导致相邻的偶极子指向相反的方向（这些相反的排列分别被称为铁电和反铁电）。此外，单个偶极子的重新定向可以从一个转移到另一个，就像一连串倒下的多米诺骨牌一样，这样，方向和旋转运动的变化有望在长距离上转移。在某些条件下，所有的偶极子预计会自发地向同一方向旋转，这样线偏振光的透射将使晶体以自发的方式从非常亮到暗的闪烁。相比之下，预计强均匀场的应用将导致所有偶极子沿着电场方向排列，这可以用来将透射光的颜色从红色改变为蓝色（非线性光学效应）。虽然这些新材料有可能显示出有趣的电、磁和弹性能力（所谓的多铁性），这些能力可以用外场控制，但在本提案中，我们概述了实验来分析它们与光的相互作用，包括折射率、极化和非线性光学特性的变化，这些变化可能是由组成偶极子的方向变化引起的。这些材料有望成为速度最快、效率最高的光开关之一。加州大学洛杉矶分校的研究小组设计了能够在固态中保持状态旋转的分子，他们将能够控制声速，并制造出有助于控制信号传输速率的设备。基于惯性偶极阵列的两动力晶体研究将为PI提供教育和培训有才华的材料化学家的机会，并开展旨在增加贫困背景的学生进入材料化学领域的研究活动。还与当地社区学院的教员建立了积极的项目合作关系。技术概述：工程旋转依赖于结构元素，这些结构元素结合了一组相对静态的晶格形成单元，以及具有围绕结构建立的晶格方向旋转和重新定向能力的偶极分量。由于元件在动态光谱的两端显示运动，这些材料被称为“两动力”。工程旋转最吸引人的一个方面是，它提供了控制热浴特性的潜力，可能有助于调节依赖声子耦合的各种量子效应。根据结构和组件的不同，工程旋转的频率范围从几赫兹到几太赫兹不等，活化能（热系数）的范围从几乎为零到大约15-20千卡/摩尔。值得注意的是，在设计良好的结晶固体中，人们可以比在非粘性液体中有更快的旋转。虽然晶体转子设计的最终目标是在广泛的时间尺度上精确控制动力学特性，以便将它们与各种材料特性相结合，但本提案中描述的惯性极性分子转子的实现提供了一些最有趣的可能性。惯性极转子构成了化学和晶体学设计的新前沿。惯性极旋转器的旋转障碍比热能低，因此在某些条件下，只要没有外力作用，它们就能保持恒定的角速度。它们也将能够在内部和强大的外部影响下非常迅速地重新定向，因此它们的涌现极化将使研究偶极自组织成为可能，从而允许出现一类具有电、磁和弹性开关能力的新型设计铁材料。在材料研究部固态和材料化学项目的支持下，该项目将集中在惯性极性旋转器的设计、合成和动态特性上。为了测试它们的性质，重点将放在测量上，这将有助于揭示内部偶极序，其形式是在准电态和铁电态或反铁电态之间的温度依赖转换。还设想了实验来分析由旋转运动和偶极子-偶极子相互作用引起的动态相关性，预测它们将遵循控制（铁电阵列）或畸变（反铁电阵列）轨迹。研究还制定了分析旋转相关性（齿轮传动）基于机械（立体）力。

NON-TECHNICAL SUMMARY: With support from the Division of Materials Research from the National Science Foundation, this research is aimed at the development of a new class of materials, known as amphidynamic crystals, which have switchable physical properties based on the reorientation and rotational motion of groups contained within their constituent molecules. With well-selected electric, magnetic and optical properties, these crystalline molecular rotors will be able to respond to external fields and change the physical properties of the material. The structures proposed for this project can be viewed as an ordered array of compasses, where every compass needle is held within a box, and it is able to affect the orientation of its closest neighbors. Since every rotating needle has positive and negative charged poles, each needle is referred to as a "dipole". It is predicted that some specific molecular compass arrangements will cause all the dipoles to point in the same direction, while others will cause adjacent dipoles to point in opposite ways (these opposite arrangements are known, respectively, as ferroelectric and antiferroelectric). Furthermore, the reorientation of a single dipole can be transferred from one to another, as in a chain of falling dominoes, such that changes in orientation and rotational motion is expected to be transferable over long distances. Under some conditions, all the dipoles are expected to spontaneously rotate in the same direction, such that the transmission of linearly polarized light would make the crystal blink, from very bright to dark, in a spontaneous manner. By contrast, it is expected that the application of a strong homogenous field will result in the alignment of all dipoles along the of direction of the electric field, which can be used to change the color of transmitted light from red to blue (a nonlinear optical effect). While these new materials have the potential of displaying interesting electric, magnetic, and elastic capabilities (so-called multiferroic properties) that can be controlled with external fields, in this proposal, experiments are outlined to analyze their interaction with light, including changes in refractive index, polarization, and nonlinear optical properties that may result from changes in the orientation of the constituent dipoles. These materials are expected to be among the fastest, most efficient optical switches. With molecules designed to maintain a state rotation in the solid state, the UCLA group will be able to control the speed of sound and create devices that will help control the rate of signal transmission. Research on amphidynamic crystals based on inertial dipolar arrays will provide the PI with opportunities to educate and train talented materials chemists and to carry out research activities aimed at increasing the number of students from underprivileged backgrounds that enter the field of materials chemistry. Active collaborations for the project have also been established with Faculty at local Community Colleges.TECHNICAL SUMMARY: Engineered rotation relies on structural elements that combine a set of relatively static, lattice-forming units, with dipolar components that possess the ability to rotate and reorient about structurally established lattice directions. With components that display motion at the two ends of the dynamic spectrum, these materials are said to be "amphidynamic". One of the most intriguing aspects of engineered rotation comes from the fact that it offers the potential for controlling the properties of the thermal bath, potentially helping modulate a variety of quantum effects that rely on phonon coupling. Depending on the structure and components, engineered rotation can have a range of frequencies that vary from a few Hertz to several Teraherz, with activation energies (thermal coefficients) that range from nearly zero up to ca. 15-20 kcal/mol. Notably, one can have faster rotation in well-designed crystalline solids than in non-viscous liquids. While the ultimate goal of crystalline rotor design is the precise control of dynamics properties over a wide range of time scales in order to interface them with various materials properties, the realization of inertial polar molecular rotors described in this proposal offers some of the most interesting possibilities. Inertial polar rotors constitute a new frontier of chemical and crystallographic design. Inertial polar rotators will have rotational barriers that are lower than thermal energy, such that under some conditions they will be able maintain a constant angular velocity for as long as there are no forces acting on them. They will also be able to reorient very rapidly in the presence of internal and strong external influences, such that their emergent polarization will make it possible to study dipolar self-organization to permit the emergence of a new class of designer ferroic materials with electric, magnetic, and elastic switching capabilities. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this project will center on the design, synthesis and dynamic characterization of inertial polar rotators. To test their properties, an emphasis will be placed on measurements that will help disclose inner dipolar order in the form of temperature-dependent transitions between paraelectric and ferroelectric or antiferroelectric states. Experiments are also envisioned to analyze their dynamic correlations resulting from rotational motion and dipole-dipole interactions, which are predicted to follow either conrotatory (ferroelectric arrays) or disrotatory (antiferroelectric arrays) trajectories. Studies are also formulated to analyze rotational correlations (gearing) based on mechanical (steric) forces.