Roof-shaped Nematogens – A New Approach towards the Thermotropic Biaxial Nematic Phase

屋顶形线虫——热致双轴向列相的新方法

• 批准号: 449759211
• 负责人: Professor Dr. Matthias Lehmann
• 金额: --
• 依托单位: Institut für Organische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/449759211?language=en
• 关键词: Roof; shaped; Nematogens; New; Approach

This project is aiming towards a new approach to realize the biaxial nematic phase in the area of low molar mass molecules. The nematic phase is a liquid crystal phase, i.e. a phase with anisotropic properties and liquid like molecular mobility, as known from LC-Displays. In the biaxial nematic phase the molecules have no positional order (they are liquid-like), but all molecular axis possess a long range orientational order – in the conventional nematic phase only the long axis is oriented owing to the molecular mobility. The aim is therefore to stop the rotation by a convenient molecular architecture. This phase is long sought because of its multiple theoretical predictions and promising applications, but never completely confirmed by the scientific community.The project is based on a recently discovered lead structure with a 1,3,5,8-tetrasubstituted anthraquinone core of a polar roof-shaped structure to which shape-persistent oligo(phenyleneethenylene)arms were attached. This molecular architecture is very close to the molecular optimum biaxiality, which is proposed to generate the biaxial nematic phase. However, the formation of a monodomain necessary for the unequivocal confirmation of phase biaxiality and the stable phase at ambient temperature could not be achieved. Therefore, the aim is to synthesize a series of roof-shaped nematogens based on the lead structure with lateral and terminal chains of different nature and lengths to optimize the molecular biaxiality and the lateral interactions along the minor axis. The latter is detrimental to guarantee the orientational order of all three molecular axes. Additionally, we synthesize derivatives, which can interact by H-bonding with substrate surfaces, such as glass. This will enable us to align the materials in monodomains, which are necessary to confirm the phase biaxiality by the applied techniques. The materials properties will be studied by polarized optical microscopy (orthoscopy, conoscopy), differential scanning calorimetry and X-ray scattering and molecular models will be setup.The knowledge of the structure-property relationship for a small series of target molecules will be used for the optimization of the molecular system. Eventually, mixtures of selected nematogens are studied in order to achieve the room temperature biaxial nematic phase. The optimized nematic molecules and their mixtures will be studied in liquid crystal cells, i.e. their alignment, polarity and switching behavior. With this research in molecular engineering, we expect to approach a real biaxial nematic phase of low molar mass molecules, which is of great basic scientific importance and can be applied in future new liquid-crystalline switching devices.

本项目的目标是在低摩尔质量分子领域实现双轴取向相的新方法。液晶相是液晶相，即具有各向异性性质和类似液体的分子移动性的相，如从LC显示器已知的。在双轴取向相中，分子没有位置顺序（它们是液体状的），但所有分子轴都具有长程取向顺序-在常规取向相中，由于分子的流动性，只有长轴取向。因此，目的是通过一种方便的分子结构来阻止旋转。这个阶段是长期以来寻求，因为它的多个理论预测和有前途的应用，但从来没有完全由科学界证实。该项目是基于最近发现的铅结构与1，3，5，8-四取代蒽醌核的极性屋顶状结构，形状持久的寡（苯乙烯）臂连接。这种分子结构是非常接近的分子最佳双轴性，这是建议产生的双轴取向相。然而，不能实现在环境温度下明确确认相双轴性和稳定相所需的单畴的形成。因此，我们的目标是合成一系列基于铅结构的具有不同性质和长度的侧链和末端链的屋顶形的聚合物，以优化分子的双轴性和沿着短轴的横向相互作用。后者不利于保证所有三个分子轴的取向顺序。此外，我们还合成了衍生物，它们可以通过氢键与基底表面（如玻璃）相互作用。这将使我们能够在单畴中排列材料，这是通过应用技术确认相双轴性所必需的。利用偏光显微镜（正射、锥光）、差示扫描量热法和X射线散射等手段研究材料的性质，建立分子模型，利用小系列目标分子的结构-性质关系知识进行分子体系的优化。最后，研究了所选择的增塑剂的混合物，以实现室温双轴取向相。将在液晶盒中研究优化的双折射分子及其混合物，即它们的取向、极性和切换行为。通过分子工程的研究，我们期望能够接近真实的低摩尔质量分子的双轴液晶相，这具有重要的基础科学意义，并可应用于未来的新型液晶开关器件。