GOALI: Chiroptical Anisotropy

两个世纪以来，人们一直在努力测量有组织的各向异性介质的手性，这给分子和材料的手性科学留下了巨大的空白。在过去的30年里，我们几乎没有学到什么东西。为了将平均的、伪标量解的热效应分解为可以与真实分子的电子结构相比较的量，需要一个分子晶体张量数据库。它们必须使用一种可靠的、易于采用的方法来测量，并且可以生成能够进行比较、分析和理解的数据量。Mueller矩阵成像偏振法是一种解决方案，因为它可以同时确定所有线性光学性质，它可以分析不完美样品的退偏振，并且适合于非正态入射的分析处理。一个没有移动光学元件的快速器件将需要四个光弹性调制器的同步操作。这从未实现过，但将通过俄勒冈州和纽约的博士后研究人员的合作，与俄勒冈州希尔斯伯勒的海因兹仪器公司进行合作。海因兹仪器公司是光弹性调制器和偏振计的领先开发商。由于涡旋各向异性是一个太大的鸿沟，一个小组无法跨越，因此对定向材料的商用交钥匙偏振仪的需求是必不可少的。有了这个装置，将测量同构分子晶体的旋光度，这些晶体有助于解释小的结构扰动。为了避免共振中激子相互作用的复杂性，我们将研究宿主晶体中染料“取向气体”的圆二色性的各向异性。穆勒矩阵显微镜和偏振仪也适用于介观结构材料，如胆甾液晶和手性雕刻超材料。恰好在两百年前（1811年），弗朗索瓦·阿拉戈第一次观察到光偏振平面沿着最高对称的方向穿过石英晶体的旋转。据说没有一种现象“对化学思想的影响比天然旋光能力更深远”（Liehr, 1954）。不幸的是，从那时起，几乎不可能沿着一般方向测量像晶体这样的有组织介质中的旋光度，因为光的电磁场在低对称性环境中受到更大的扰动，掩盖了感兴趣的现象。因此，我们仍然不了解分子中旋光的方向依赖，这是一种基本的光-物质相互作用。我们的项目旨在开发一种仪器，可以快速准确地测量任何介质中光的偏振状态，以便我们可以得出必要的量。该装置基于光弹性调制器，可以以每秒约50,000次的速率改变光的偏振状态。使用四个这样的调制器，由我们的GOALI合作伙伴Hinds仪器制造，我们可以产生一个复杂的信号，可以用阿拉戈的同事之一的傅立叶的数学技术来处理。我们与布朗克斯科学技术学院建立了合作关系，这是一所服务不足的公立高中，98%的学生以西班牙语为母语。除了在夏季和学年期间在我们的实验室提供研究机会外，我们还提供SAT辅导，这是富裕学区普遍采用的优势。我们相信，培养科学家，特别是那些来自代表性不足的群体的科学家，首先需要在学生内部一个接一个地培养科学身份，并确保基本知识得到关注。

TECHNICALThe two-century struggle to measure chiroptical properties of organized, anisotropic media leaves an enormous hole in the science of molecular and materials chirality. What little has been learned during the past three decades has come haltingly. In order to unravel averaged, pseudo-scalar solution chiroptical effects into quantities that can be compared with electronic structures of real molecules, a database of molecular crystal tensors is required. They must be measured using a methodology that is robust, can be easily adopted, and can generate the quantity of data that enables comparison, analysis, and understanding. Mueller matrix imaging polarimetry is the solution because all linear optical properties can be determined simultaneously, it can assay depolarization in imperfect samples, and is suited to the treatment of non-normal incidence analytically. A fast device without moving optical components will require the synchronous operation of four photoelastic modulators. This has never been achieved but will be carried out with Hinds Instruments of Hillsboro, Oregon, a leading developer of photoelastic modulators and polarimeters, through collaboration of postdoctoral researchers in Oregon and New York. The need for a commercial, turnkey polarimeter for oriented materials is essential because chiroptical anisotropy is a chasm too large for one group to bridge. With this device, the optical rotation of isomorphous molecular crystals that lend themselves to the interpretation of small structural perturbations will be measured. To avoid complications associated with excitonic interactions in resonance, the anisotropy of circular dichroism of "oriented gases" of dyes in host crystals will be studied. Mueller matrix microscopes and polarimeters are also applicable to meso-structured materials such as cholesteric liquid crystals and chiral sculpted meta-materials. NON TECHNICALExactly two hundred years ago (1811) François Arago first observed the rotation of the plane of light polarization passing through a crystal of quartz along the direction of highest symmetry. It is been said that no phenomenon "has had so profound an effect on chemical thought as that of natural optical rotatory power" (Liehr, 1954. Unfortunately, since that time it has been almost impossible to measure optical rotation in organized media like crystals along general directions because the electromagnetic field of light suffers greater perturbations in low-symmetry environments that mask the phenomenon of interest. Thus, we remain ignorant about the orientation dependence of optical rotation in molecules, a fundamental light-matter interaction. Our project is aimed at developing an instrument for measuring the polarization state of light in any medium quickly and accurately enough so that we can derive the essential quantities. The device is based on photoelastic modulators that can change the polarization state of light at a rate of ~50,000 times per second. Using four such modulators, built by our GOALI partner, Hinds instruments, we can generate a complex signal that can be treated by the mathematical techniques of one of Arago's colleagues', Fourier. We have established a relationship with the Bronx Academy of Science and Technology, an underserved public high school with 98% native Spanish speakers. We provide, in addition to research opportunities in our lab during the summer and academic year, SAT tutoring, an advantage commonly exercised in wealthy school districts. We are convinced that creating scientists, especially those from underrepresented groups, requires first developing within students, one-by-one, scientific identities, and ensuring that the basics are attended.