Kinetically Trapping the Self-Assembly and Photophysical Properties of Liquid Crystals

非技术综述：在材料研究部固态和材料化学与凝聚态物理项目的支持下，这项研究考察了微小的光敏夹杂物，如小分子(即可切换掺杂剂)对远程螺旋结构的影响，从而影响液晶的光物理性质(液晶是液晶显示器(LCD)电视中发现的同一类型材料)。Aprahamian团队研究了控制可切换掺杂剂和宿主LC之间相互作用的基本因素，以获得对如何更好地控制此类现象的见解。该项目的目的是了解这一策略是否可以用于编程LCS的光学属性。这些知识反过来又推动了从主动智能表面到传感器、滤色器和响应性反射器的各种应用。Aprahamian和他的小组还参加教育和外联活动，这些活动包括：i)让来自不同教育水平和背景的高中生和本科生参与研究；ii)增加公众对重要化学概念的了解和欣赏。例如，PI的团队使用互动演示向公众解释荧光团是如何工作的。该小组的公众宣传和参与与STEM相关的活动，如达特茅斯科学日，有助于向广大受众传播该小组的工作。技术概述：自适应液晶(LCS)被广泛应用于从主动智能表面到传感器、滤色器和响应性反射器的各种应用中。手性可切换掺杂剂通常是这些应用的核心，尽管它们与宿主LC之间的相互作用的性质，以及这些相互作用如何控制手性LC的自组装和螺旋扭曲，这些都是导致LC的光物理性质的原因，但人们对此知之甚少。在材料研究部固态和材料化学与凝聚态物理项目的帮助下，Aprahamian小组进行了结构-性质分析，以了解分子间相互作用和结构参数，这些因素既控制着螺旋扭转力(即手性掺杂剂扭转向列相的能力)，也控制着手性光致变色掺杂剂(即肼带)切换时螺旋扭转力的变化。该小组还使用双稳态的Hydrazone光开关来动态捕获LC的自组装，从而捕获从其表面反射的颜色。总体而言，这项研究增强了可供从业者使用的工具箱和能力，从而允许实现自适应LC材料预定的众多应用。此外，Aprahamian和他的团队还参与了外联活动，以加强和扩大该组织与当地学校和科学博物馆的非正式和正式科学教育伙伴关系和网络。该奖项反映了NSF的法定使命，并通过使用基金会的智力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 Summary:With support from the Solid State and Materials Chemistry and Condensed Matter Physics Programs in the Division of Materials Research, this research examines the effect that tiny amounts of light-sensitive inclusions, such as small molecules, (i.e., switchable dopants) have on the long-range helical structure, and hence, photophysical properties of liquid-crystals (LCs – the same type of material found in Liquid Crystal Display (LCD) televisions). The Aprahamian group studies the fundamental factors that govern the interactions between the switchable dopant and host LC to gain insights into how to better control such phenomena. The aim of the project is to understand if this strategy can be used in programming the optical properties of the LCs. This knowledge in turn advances applications ranging from active smart surfaces, to sensors, color filters, and responsive reflectors. Aprahamian and his group also participate in educational and outreach activities that i) engage high-school and undergraduate students from different educational levels and backgrounds in research, and ii) increase public knowledge and appreciation of important chemical concepts. For example, the PI’s group uses interactive demonstrations to explain to the public how fluorophores work. The group’s public outreach and participation in STEM-related events, such as the Dartmouth Science Day, help disseminate the group’s work to broad audiences. Technical Summary: Adaptive liquid crystals (LCs) are used in a myriad of applications ranging from active smart surfaces to sensors, color filters, and responsive reflectors. Chiral switchable dopants are usually at the heart of these applications, though the nature of the interactions between them and the host LC, and how these interactions control the self-assembly and helical twist of the chiral LC, which are responsible for the LC’s photophysical properties, is poorly understood. With the help of this grant from the Solid State and Materials Chemistry and Condensed Matter Physics Programs in the Division of Materials Research the Aprahamian group conducts structure-property analyses to develop an understanding of the intermolecular interactions and structural parameters that control both the helical twisting power (i.e., the ability of a chiral dopant to twist a nematic phase) and the change in helical twisting power upon switching of chiral photochromic dopants (i.e., hydrazones). The group also uses the bistable hydrazone photoswitches to kinetically trap the self-assembly of the LCs, and hence, the colors reflected from their surfaces. Overall, this research enhances the toolbox and capabilities available to practitioners, thus allowing for the realization of the numerous applications that adaptive LC materials are slated for. Additionally, Aprahamian and his group are involved in outreach activities that strengthen and extend the group's informal and formal science education partnerships and networks with local schools and science museums.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.