Tail-Free Discotic Liquid Crystals

非技术摘要：液晶是一种化合物，其“相”（物质的状态）比液体更有序，但比晶体排列更无序。液晶是一个庞大的显示产业的基础，也是半导体等潜在的游戏规则改变者，使廉价的柔性电子产品、有机光伏和传感器成为可能。该项目由美国国家科学基金会材料研究部固态与材料化学项目资助，打破了液晶（LC）分子设计的范式，并推动了对这些重要材料的理解和使用的转变。液晶分子，尤其是盘状液晶分子，几乎总是由一个刚性的中心“核”构成，周围是长而灵活的“尾”，这些“尾”会不断改变形状。这些高度动态的尾迹对LC的计算机建模提出了挑战，也经常危及LC半导体的传导。社会如何才能更好地从LC半导体等材料中获益，同时避免尾翼带来的限制？一种新的光驱动合成提供了解决这个难题的方法，揭示了基于简单构建块和少量添加氟原子的多个无尾盘状lc家族。除了提供具有技术价值的lc，这些材料还有望解决一个难题：为什么有些分子能形成lc，而其他密切相关的分子却不能？为了回答这个问题，并深入了解新半导体的设计和合成，研究人员将实验和理论紧密结合起来。利用分子的计算模型来了解它们相互作用的细节，新的化学合成以及结构和电子特性的测量，研究人员确定了新的无尾lc，并增加了对这些迷人系统中驱动液体结晶度的理解。此外，这个项目还支持一个公共推广项目，“什么？在这里，日常的电子产品将在一个引导的、有趣的氛围中被解构。透过是次活动，市民有机会了解日常使用的电子科技，而小朋友亦会对STEM教育产生兴趣。技术摘要：液晶在显示工业中的重要性是众所周知的，而盘状液晶是很有前途的有机半导体。液晶，尤其是盘状液晶，几乎总是由一个刚性核心组成，周围是柔性的、高动态的、通常饱和的彗尾。盘状LCs家族通常是根据经验发现的，理论指导有限，部分原因是尾部建模的复杂性。最近对氟化三苯和其他熔合环芳烃的研究表明，存在多个无尾盘状烃族（tfdlc）。这些新材料有望阐明一个难题：为什么有些分子能形成lc，而其他密切相关的分子却不能？tfdlc是结构刚性的、简单的模型系统，比传统的带尾盘状lc更接近于lc的理想模型。在这个由美国国家科学基金会材料研究部固态和材料化学项目资助的项目中，利用tfdlc的小尺寸和刚性来执行分子间势的量子从头算，并实现真实的模拟，以发现驱动液体结晶度的力。这些模拟是建立在文献方法的基础上的，能够对真实分子进行有效的蒙特卡罗和分子动力学，包括各向异性势和空间相互作用的影响。实验中，对所有的tfldc进行了全面的表征，包括飞行时间电荷输运和晶体和盘状相的x射线衍射。研究人员将实验结果与模拟结果联系起来。从这项工作中得出的设计原则预计将导致新的有机半导体类别，以探索无序在传输中所起的作用，使用氟化来增强电子迁移率，以及由于没有尾巴的强柱间相互作用而导致的维度影响。研究了更大的tfdlc，以探索潜在的高迁移率盘状半导体，以提高器件的设计和性能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract:Liquid crystals are compounds that display "phases" (states of matter) that are more ordered than liquids, but less ordered than crystalline arrangements. LCs are the basis of a huge display industry as well as potential game changers as semiconductors, enabling cheap flexible electronics, organic photovoltaics, and sensors. This project, funded by the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, breaks a paradigm in liquid crystal (LC) molecular design and drives a transformation in the understanding and use of these important materials. Liquid crystal molecules, and especially discotic (disc-like) LCs, are nearly always built of a rigid central "core" surrounded by long, flexible "tails", which constantly change shape. These highly dynamic tails represent a challenge to computer modeling of LCs and also often compromise conduction in LC semiconductors. How can society better reap the benefits of materials like LC semiconductors while avoiding the limitations imposed by tails? A new light-driven synthesis offers a way out of this conundrum, revealing multiple families of tail-free discotic LCs based on simple building blocks with a few added fluorine atoms. Besides offering LCs of technological interest, these materials promise to shine light on a difficult question: Why do some molecules form LCs while other closely related ones do not? To answer this question and gain insights into the design and synthesis of new semiconductors, the researchers tightly couple experiment and theory. Using computational modeling of the molecules to understand the details of their interaction with each other, new chemical syntheses and measurements of structural and electronic properties the researchers identify new tail-free LCs and increase the understanding of what drives liquid crystallinity in these fascinating systems. Additionally, this project supports a public outreach project, "What?s in the Box?", in which everyday electronics will be deconstructed in a guided, fun atmosphere. Through this activity the public gets an opportunity to better understand everyday electronic technology, and children might become more interested in STEM education.Technical abstract:The importance of liquid crystals (LCs) in the display industry is well known, and discotic LCs are promising organic semiconductors. Liquid crystals, and especially discotic LCs, are nearly always comprised of a rigid core surrounded by flexible, highly dynamic, often saturated tails. Families of discotic LCs are usually found empirically, with limited theoretical guidance, partly due to the complexity of modeling the tails. Recent work on fluorinated triphenylene and other fused-ring aromatics demonstrates that there are multiple families of tail-free discotic LCs (TFDLCs). These new materials promise to illuminate a difficult question: Why do some molecules form LCs while other closely related ones do not? TFDLCs are structurally rigid, simple model systems much closer to idealized models of LCs than conventional discotic LCs with tails. In this project, funded by the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, TFDLCs' small size and rigidity are leveraged to perform quantum ab-initio calculations of intermolecular potentials and enable realistic simulations to discover what forces drive liquid crystallinity. These simulations are built on literature methods, enabling efficient Monte Carlo and molecular dynamics for real molecules including effects of anisotropic potentials and steric interactions. Experimentally, all of TFLDCs are comprehensively characterized, including time-of-flight charge transport and x-ray diffraction in the crystal and discotic phases. The researchers correlate experimental results with the simulations. Design principles, resulting from this work are expected to lead to new classes of organic semiconductors to probe the role that disorder plays in transport, the use of fluorination to enhance electron mobility, and the effects of dimensionality due to strong intercolumn interactions in the absence of tails. Larger TFDLCs are studied to explore potential high mobility discotic semiconductors to enhance device design and performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.