Mirror-Symmetry Breaking in Self-Assembled Nanostructured Functional Materials

• Applicant: Dr. Mohamed Alaasar
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424355983

Supramolecular photoswitchable materials are extremely interesting for the development of intelligent materials. In this project novel classes of such nanostructured self-assembled functional materials are planned to be synthesized and investigated. This aims to understand the fundamental factors leading to macroscopic chirality in fluid systems formed by achiral molecules, which could provide useful insights into the understanding of spontaneous development of homochirality and lead to functional chiral soft materials. As proved during the first period of the project, different types of liquid crystalline phases including mirror-symmetry broken isotropic liquids and the technologically important chiral cubic phases were found for achiral materials and their formation was successfully controlled using different tools such as alkyl chain engineering or core fluorination and efficiently modified by light irradiation. Also, a new liquid crystalline phase was discovered, and its structure was solved. The targets of the second period are inspired from these promising results, which are planned to be extended to answer remaining open questions. Therefore, the relations between the formation of helical networks and deformation of the cubic lattice or generation of new modes of helical self-assembly in the tetragonal phases are planned to be investigated. Additionally, a cross-over between helix formation in network phases of polycatenars and mirror symmetry breaking in mesophases of bent-core materials and mesogenic dimers, is planned to be achieved. Moreover, the target materials will be tested for technological application, especially those requiring switchable optical and chiroptical properties and fast charge transfer. To deal with these challenges, novel classes of photoswitchable liquid crystalline materials will be synthesized and investigated in detail. These materials are planned to combine features of both, bent-core and polycatenar mesogens. As major building blocks oxadiazole and bithiophene will be used. Moreover, the effect of molecular chirality on the formation of mirror-symmetry broken mesophases will be investigated. Full characterization of the target materials will be performed using different techniques such as X-ray diffraction, electro-optical investigations and Second Harmonic generation. This will be mainly done in fruitful collaborations which were established in the first period and should provide a complete understanding of the different types of mirror-symmetry broken phases exhibited by these materials. As well it is expected to provide guidelines for designing new types of chiral photoswitchable materials which could be applied in electro-optical or chiroptical switches, for displays and communication applications.

• DFG Programme: Research Grants