Liquid crystalline helicenes for next generation magneto optic applications
Solid State and Surface Chemistry, Material Synthesis
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
Faraday rotation is a magneto-optical phenomenon that leads to a rotation of linearly polarized light by a certain angle (β) while passing through any matter under the influence of a magnetic field (B). The extent of the rotation also depends on the thickness (l) and the material specific Verdet constant (V). Most materials known for Faraday rotation are inorganic crystals, but their application is severely limited by their brittleness and low tuneability. Utilizing this effect in organic materials could lead to the realization of low cost, flexible magnetic field sensors that can operate at room temperature. A technology with the potential to transform several real-world applications such as low-power computation and memory devices, non-destructive material safety testing and high spatial resolution neuroimaging. However, several key challenges will need to be addressed which include the development of novel organic materials for Faraday rotation and further understanding of the fundamental (supra-) molecular parameters that are required for high Verdet constants. The initial objective of the project was the study of chiral liquid crystalline, because both chirality as well as liquid crystallinity are suggested in the literature be beneficial for high Verdet constants. While the synthesis of two helicenes was successful, thin films did not show any Faraday rotation in a measurable extent. In parallel I was involved in a project studying the Faraday rotation of chiral polymer blends. We could shed light on the role of chiral supramolecular assemblies in annealed films of such systems and their role in enhancing the Faraday rotation while achieving state-of-the-art Verdet constants > 105 °/Tm. Those results reveal the real influence of chirality on Faraday rotation and will lead to novel and disruptive designs of magneto-optically active materials. With those promising results at hand, I turned to my attention to Faraday rotation of (chiral-) polymers. While working on F8T2 and F8Se2 polymers, I discovered a potential link between strong Faraday rotation to certain types of extended aggregation in polymers. If this discovery which is currently under further investigation, holds true, it would provide another handle for the enhancement of Verdet constants in organic materials. I also studied a variety of other organic compounds but most of these materials did not show measurable Verdet constants. A strong response was however observed for a π-extended helicene. This shows that it is indeed possible to achieve high Faraday rotation from certain compounds with helical frameworks. Currently, these projects are still ongoing, but we will to be able to publish the results soon.
