RUI: Investigations of the cybotactic nematic phase in bent-core liquid crystals

液晶显示器（LCD）存在于手机、电视和电脑屏幕等设备中。这些器件是由具有液晶相的化合物构成的。处于这一阶段的分子在电场的作用下可以重新定向，从而改变它们的光学性质。在固态和材料化学计划的资助下，化合物的制备和研究显示出一种独特的液晶相，其中分子可能经历更快的重新定向。这可能会导致更快的液晶显示，这将提高设备的光学质量，并降低设备消耗的能量。普吉特海湾大学的本科生直接参与了nsf资助的研究的各个方面。参与研究为学生提供了一个极好的机会来提高他们的批判性思维能力。这些经历为学生提供了强有力的技术培训，为他们进入科学领域的劳动力市场或攻读化学或相关领域的研究生课程提供了良好的服务。在普吉特海湾大学，57%的学生是女性，25%的学生认为自己是有色人种。美国国家科学基金会的支持有助于PI为来自STEM领域代表性不足的群体的学生提供研究机会。自从双轴向列相（Nb）在高熔点弯核化合物中被报道以来，人们一直对它有浓厚的兴趣；使用这一相位制造的液晶显示器具有进行更快的电光开关的潜力。然而，对于这一相是否真的是双轴向列相存在争议；最近的证据表明，这一阶段由层状（近晶）结构域（胞浆簇）组成，只有在较大的长度尺度上才显示向列顺序。这项来自固态和材料化学项目的资助支持了各种恶二唑基化合物的合成，并分析了它们的液晶行为。这些研究提供了关键的见解如何不同的结构因素影响向列相的稳定性和性质在弯核化合物。通过制备一系列具有1)各种侧基，2)高极性取代基和3)酰胺键的化合物，PI和他的学生可以生成结构-性质关系，旨在了解哪些结构特征产生具有低起始温度的向列相。目标化合物的合成和相行为的初步分析（使用偏光显微镜和差示扫描量热法）在普吉特海湾大学进行。PI的合作者通过x射线衍射研究这些化合物，这提供了向列相内分子组织的详细信息。他们还对具有高极性基团的衍生物进行了电光实验，因为这些衍生物是铁电开关的候选者。具有低温向列相的导数将有利于物理学家的基础研究和可能应用的研究。来自NSF的支持帮助PI为来自STEM领域代表性不足的群体的本科生提供研究机会。

Non-technical summaryLiquid crystal displays (LCD) are found in devices such as cell phones and television and computer screens. These devices are constructed using compounds that exhibit a liquid crystal phase. Molecules in this phase can be reoriented in the presence of an electric field, which changes their optical properties. With support from this grant by the Solid State and Materials Chemistry Program compounds are prepared and studied that exhibit a unique type of liquid crystal phase in which the molecules can potentially undergo faster reorientation. This could lead to faster liquid crystal displays, which would improve the optical quality of the devices, and lower the amount of energy consumed by the devices. Undergraduate students at the University of Puget Sound are directly involved in all aspects of the NSF-funded research. Participation in research offers an excellent opportunity for students to enhance their critical thinking skills. These experiences provide students with strong technical training that will serve them well as they enter the workforce in a scientific field or pursue graduate studies in Chemistry or a related area. At the University of Puget Sound, 57% of the students are women, and 25% of the students identify as students of color. This support from NSF helps the PI to provide research opportunities to students from groups who are typically underrepresented in STEM fields. Technical summaryThere has been intense interest in the biaxial nematic phase (Nb) since it was reported in high melting bent-core compounds; liquid crystal displays fabricated using this phase have the potential to undergo faster electro-optic switching. However, there is controversy as to whether this phase is truly a biaxial nematic phase; recent evidence suggests the phase consists of layered (smectic) domains (cybotactic clusters) that show nematic order only across larger length scales. This grant from the Solid State and Materials Chemistry Program supports the synthesis of a variety of oxadiazole-based compounds, and analysis of their liquid crystalline behavior. These studies provide critical insight into how various structural factors affect the stability and nature of the nematic phase in bent-core compounds. The preparation of series of compounds with 1) various lateral groups, 2) highly polar substituents, and 3) amide linkages allow the PI and his students to generate structure-property relationships, with the intention to learn what structural features yield a nematic phase with a low onset temperature. Synthesis of the target compounds and initial analysis of phase behavior (using polarizing microscopy and differential scanning calorimetry) are carried out at the University of Puget Sound. Collaborators of the PI study the compounds by X-ray diffraction, which provides detailed information about the molecular organization within the nematic phase. They also carry out electro-optic experiments on the derivatives with highly polar groups as these are candidates for ferroelectric switching. Having derivatives with low temperature nematic phases would facilitate both fundamental study by physicists and investigation of possible applications. This support from NSF helps the PI to provide research opportunities to undergraduate students from groups who are typically underrepresented in STEM fields.