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

非技术总结：在材料研究部固态和材料化学以及凝聚态物理项目的支持下，本研究考察了微量光敏夹杂物（如小分子）（即，可切换掺杂剂）具有长程螺旋结构，因此具有液晶（LC-在液晶显示器（LCD）电视中发现的相同类型的材料）的光物理性质。Aprahamian小组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，以深入了解如何更好地控制此类现象。该项目的目的是了解这种策略是否可以用于编程LC的光学特性。这些知识反过来又推动了从有源智能表面到传感器、滤色器和响应式反射器的应用。Aprahamian和他的团队还参与教育和推广活动，i）让来自不同教育水平和背景的高中和本科生参与研究，ii）增加公众对重要化学概念的了解和欣赏。例如，PI的团队使用交互式演示向公众解释荧光团的工作原理。该小组的公共宣传和参与STEM相关活动，如达特茅斯科学日，有助于向广大受众传播该小组的工作。 技术总结：自适应液晶（LC）用于从有源智能表面到传感器、滤色器和响应反射器的无数应用中。手性可切换掺杂剂通常是这些应用的核心，尽管它们与主体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（这是LC的电物理性质的原因），却知之甚少。在材料研究部的固态和材料化学以及凝聚态物理计划的资助下，Aprahamian小组进行了结构-性质分析，以了解控制螺旋扭曲力（即，手性掺杂剂扭转螺旋相的能力）和手性光致变色掺杂剂转换时螺旋扭转力的变化（即，腙）。该小组还使用双酰腙光电开关来动力学捕获LC的自组装，从而捕获从其表面反射的颜色。总的来说，这项研究增强了从业者可用的工具箱和能力，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一些外展活动，这些活动加强和扩大了该团队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，并被认为值得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来支持。

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.