Liquid crystalline helicenes for next generation magneto optic applications

• Applicant: Dr. David Reger
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation ; Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2022 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 500635930

The detection of small magnetic fields at room temperature, with flexible sensors, has the potential to revolutionize a great number of applications. Among those are non-destructive material testing (e.g., in aircraft construction), new possibilities to design data storage systems and even quantum computers or high-resolution brain imaging techniques. A very promising possibility to realize such magnetic field sensors are flexible, magneto optically active organic compounds. The basis for this is the Faraday effect. It leads to a turning of the plane of polarization of electromagnetic waves by a certain angle, when they pass through matter which is under the influence of a magnetic field. The strength of the Faraday effect is mainly determined by the material dependent Verdet constant (V). Furthermore, the ratio Verdet constant/absorption coefficient (V/α) is of great importance. Unfortunately, few is known how organic compounds have to be built up to exhibit a high V and a good ratio V/α. However, there are indications that aspects like chirality and molecular order in the thin film increase V. Furthermore, heavy, polarisable atoms like sulfur enhance non-resonant optical phenomena, which leads to a better V/α ratio. From this, the following goals for the project are deduced: - The synthesis and characterization of different liquid crystalline helicenes. The fabrication of thin films from these materials and investigations regarding the Faraday effect. This will lead to first insights into the magneto-optical properties of such helicenes as they were not studied before. Investigation of the influence of chirality on V by comparison of enantiomerically pure helicenes and racemic mixtures. Investigations regarding supramolecular order on V. This will be achieved by changing the supramolecular structure in the helicene films via different fabrication techniques and post-treatments (e.g., thermal annealing). Investigation of the influence of different amounts of polarisable atoms (e.g., sulfur or selenium) on the ration of V/α. Investigations regarding the influence of electronic polarization of the helicene π system on V by attachment of different electron accepting or donating substituents. Overall, this should lead to novel insights and a deeper understanding of magneto-optical effects, especially the Faraday effect in organic compounds. Furthermore, it is expected that liquid crystalline helicenes could exhibit very high Verdet constants due to their molecular and supramolecular chirality, which would open new possibilities in that field of research.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Professor Matthew J. Fuchter, Ph.D.