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

非技术性总结：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类新的材料，称为两性晶体，其具有基于其组成分子中所含基团的重定向和旋转运动的可切换物理特性。 通过精心选择的电，磁和光学特性，这些晶体分子转子将能够响应外部场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，其中每个罗盘针都放在一个盒子里，它能够影响它最近邻居的方向。 由于每个旋转的针都有正负两极，每个针都被称为“偶极子”。 据预测，一些特定的分子罗盘安排将导致所有的偶极子指向同一方向，而其他人将导致相邻的偶极子指向相反的方向（这些相反的安排被称为铁电和反铁电）。此外，单个偶极子的重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，定向和旋转运动的变化预计可以在长距离上转移。 在某些条件下，所有的偶极子都将自发地沿同一方向旋转，这样线性偏振光的传输将使晶体以自发的方式从非常亮到暗闪烁。 相比之下，预期强均匀场的施加将导致所有偶极子沿电场的方向沿着对准，这可用于将透射光的颜色从红色改变为蓝色（非线性光学效应）。 虽然这些新材料具有显示有趣的电，磁和弹性能力（所谓的多铁性），可以控制与外部领域的潜力，在本提案中，实验概述了分析它们与光的相互作用，包括折射率，偏振和非线性光学特性的变化，可能会导致在组成偶极子的方向的变化。 这些材料有望成为最快、最高效的光开关之一。 通过设计分子以保持固态的状态旋转，加州大学洛杉矶分校的研究小组将能够控制声音的速度，并创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双动晶体研究将为PI提供教育和培训有才华的材料化学家的机会，并开展旨在增加进入材料化学领域的贫困背景学生数量的研究活动。该项目还与当地社区学院的教师建立了积极的合作关系。技术概要：工程旋转依赖于结构元素，这些结构元素联合收割机一组相对静态的晶格形成单元，以及具有旋转能力的偶极组件，并围绕结构上建立的晶格方向重新定向。 由于这些材料的成分在动态光谱的两端显示运动，因此这些材料被称为“两亲性”。 工程旋转最有趣的方面之一来自这样一个事实，即它提供了控制热浴特性的潜力，可能有助于调节依赖于声子耦合的各种量子效应。 根据结构和组件的不同，工程旋转可以具有从几赫兹到几太赫兹的频率范围，激活能（热系数）的范围从几乎为零到大约为零。15-20千卡/摩尔。 值得注意的是，在设计良好的结晶固体中，旋转速度比在非粘性液体中更快。 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。 惯性极旋转器将具有低于热能的旋转屏障，使得在某些条件下，只要没有力作用在它们上，它们就能够保持恒定的角速度。它们也将能够在内部和强烈的外部影响下非常迅速地重新定向，这样它们的出现极化将使研究偶极自组织成为可能，从而允许出现一类新的具有电，磁和弹性开关能力的设计师铁性材料。 在材料研究部固态和材料化学计划的支持下，该项目将集中在惯性极性旋转器的设计，合成和动态表征上。 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秩序的形式，顺电和铁电或反铁电状态之间的温度依赖性的转变。 实验还设想分析它们的动态相关性产生的旋转运动和偶极-偶极相互作用，这是预测遵循顺旋（铁电阵列）或反旋（反铁电阵列）的轨迹。 研究还制定分析旋转相关性（齿轮）的基础上机械（空间）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.