Arrays of Molecular Dipolar Rotors

在固态与材料化学项目的支持下，研究团队将在设计导向材料合成方面开展跨学科项目，该项目需要与物理系的同事密切互动。该项目旨在制备和表征一种迄今未知的介电材料，该材料基于人工偶极分子转子排列在二维网格中。这种材料在自然界中是不存在的，对于信号处理，特别是对于电子电路中模拟元件的小型化非常有用，例如蜂窝电话中的模拟元件。一名博士后和几名本科生将接受跨学科培训（有机合成、各种光谱和其他物理技术、基础材料理论）。该项目将吸引本科生、K-12学生和代表性不足的少数民族学习纳米科学。技术摘要：新的二维材料将在Langmuir-Blodgett （LB）槽上组装，并转移到光刻图案的固体基板上。专门合成的棒状转子分子在与表面垂直的轴上的两个三甲烯单元之间携带一个偶极旋转体，在一端携带一个羧基（术语分子转子用于具有可旋转部分的分子，称为旋转体）。初始掠入射x射线散射和其他数据表明，这种类型的分子在水相上自组装成Langmuir单层。该组件的结构特点是将三烯单元联锁成双层三角模式，在甲板之间几乎可以自由旋转的偶极子。偶极子和它们的大小之间的距离是这样的，只要可以制备足够大的二维单晶畴，在第一个近似中基态应该是铁电的，居里温度高于环境温度。通过Michl实验室红外光谱部分的电二色性和Rogers实验室的介电光谱学来研究转移的单层（和多层）中的旋转体动力学。理论预测，当远距离偶极相互作用支配局部旋转位垒时，铁电有序与异常低速极性声波的存在。

Non-technical AbstractWith the support from the Solid State and Materials Chemistry program, the research team will work on an interdisciplinary project in design-directed material synthesis that calls for close interactions with colleagues in the Physics department. The project aims to prepare and characterize a so far unknown class of dielectric materials based on artificial dipolar molecular rotors arranged in a 2-dimensional grid. Such materials do not occur in nature and would be useful for signal processing and specifically for minituarization of analog components in electronic circuitry such as that found in cellular telephones. A post-doctoral student and several undergraduates will receive interdisciplinary training (organic synthesis, a variety of spectroscopic and other physical techniques, and underlying materials theory). The project will attract undergraduate students, K-12 students, and under-represented minorities to nanoscience.Technical AbstractThe new 2-dimensional materials are to be assembled on a Langmuir-Blodgett (LB) trough and transferred to a lithographically patterned solid substrate. The specifically synthesized rod-like rotor molecules carry a dipolar rotator between two triptycene units on an axle normal to the surface, and a carboxylic group at one end (the term molecular rotor is used for a molecule with a rotatable part, which is called the rotator). Initial grazing-incidence X-ray scattering and other data demonstrate that molecules of this type self-assemble into a Langmuir monolayer on an aqueous subphase. The structure of the assembly is characterized by an interlocking of the triptycene units into a double-decker trigonal pattern, with almost freely rotatable dipoles between the decks. The distance between the dipoles and their magnitude are such that as long as sufficiently large 2-dimensional single-crystal domains can be prepared, in the first approximation the ground state should be ferroelectric, with a Curie temperature above ambient. Rotator dynamics in the transferred monolayers (and multilayers) are to be studied by electric dichroism in the infrared part of the spectrum in the Michl laboratory and by dielectric spectroscopy in the Rogers laboratory. Theory predicts the existence of ferroelectric ordering with unusually low velocity polar sound waves when long-range dipolar interactions dominate local steric barriers to rotation.