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

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.