Materials Chemistry of Self-Assembling Dyes

有机染料在我们的环境中无处不在，并且对特定技术具有改进性能的新染料的需求不断增加。艾希霍恩小组开发的染料可以组装成类似于传统液晶的特定分子排列。在分子长度尺度（纳米结构）上对材料结构的这种类型的控制对于调节染料膜和颗粒的性质与染料本身的分子结构一样重要。在该提案中，提出了有机染料的新设计标准，即（1）自组装成各向异性材料，芳族基团之间具有强相互作用，（2）形成一个分子厚的纳米结构膜。具有这些结构的材料有望产生前所未有的性能，有利于它们在广泛的不同技术中的应用，这些技术具有商业重要性，例如有机半导体，高压润滑剂，光学薄膜和传感器。主题1挑战了设计由较大共轭/芳族结构组成的有机分子和聚合物所需的柔性侧链的范式，因为这些刚性芳族结构是不溶性的，难以加工。明智地选择侧链的类型及其连接点也已被证明可以增强对材料中这些分子的排列和对齐的控制。然而，柔性侧链的利用具有重要的缺点，因为它通常降低分子的热稳定性，排除某些纯化和加工方法（例如升华），不利于某些堆积排列，并且阻碍在作为有机半导体的应用中的电荷传输。这里提出的工作的主要目标是制定合理的分子设计标准的侧链自由的多环芳香族染料，可以加工成类似的分子排列和识别材料的性能是上级的那些侧链含有类似物。课题2的研究建议建立在该小组最近成功控制界面处薄膜中染料分子排列的基础上。多环芳族染料通常形成堆叠分子的聚集体，并在界面处以边缘取向自组装。这种分子排列改变了它们的光吸收，并经常抑制它们的荧光。它还在表面上产生相当致密的层，这阻碍了染料分子与环境中的分子（例如分析物）和基底表面相互作用。Eichhorn的小组已经开发出了两亲性染料，这些染料相对于界面是平的，这里提出的研究的主要目标是优化这些类型染料分子的分子设计标准，交联它们的薄膜以增强稳定性，并证明它们在传感，表面涂层和纳米颗粒功能钝化方面的应用优势。

Organic dyes are ubiquitous in our environment and new dyes with improved properties for specific technologies are constantly in demand. The Eichhorn group develops dyes that assemble into specific molecular arrangements similar to conventional liquid crystals. This type of control over the structure of materials at molecular length scales (nanostructure) is as important for the adjustment of properties of dye films and particles as the molecular structure of the dye itself. In this proposal new design criteria are proposed for organic dyes that (1) self-assemble into anisotropic materials with strong interactions between aromatic groups and (2) form one molecule thick films of defined nanostructures. Materials with these structures are expected to generate unprecedented properties that benefit their application in a wide range of different technologies that are commercially important, such as organic semiconductors, high pressure lubricants, optical films, and sensors. Topic 1 challenges the paradigm flexible side-chains are required for the design of organic molecules and polymers consisting of larger conjugated/aromatic structures because these rigid aromatic structures are otherwise insoluble and difficult to process. Judicious choice of the types of side-chains and their attachment points has also been shown to enhance control over the arrangement and alignment of these molecules in a material. However, the utilization of flexible side-chains has important disadvantages as it often lowers thermal stability of the molecules, excludes certain purification and processing methods (e.g. sublimation), disfavors certain packing arrangements, and hinders charge transport in applications as organic semiconductors. The main objective of the work proposed here is to develop rational molecular design criteria for side-chain free polycyclic aromatic dyes that can be processed into similar molecular arrangements and identify materials properties that are superior to those of side-chain containing analogues. Research proposed for topic 2 builds on the group's recent success in controlling the alignment of dye molecules in thin films at interfaces. Polycyclic aromatic dyes commonly form aggregates of stacking molecules and self-assemble with an edge-on orientation at interfaces. This molecular arrangement alters their light absorption and often suppresses their fluorescence. It also generates a rather dense layer on a surface that hinders the dye molecules from interacting with molecules in the environment, such as analytes, and the substrate surface. Eichhorn's group has developed amphiphilic dyes that orient flat-on with regard to an interface and the main objective of the research proposed here is to optimize the molecular design criteria for these types of dye molecules, to cross-link their thin films for enhanced stability, and to demonstrate their advantages for applications in sensing, surface coatings, and functional passivation of nanoparticles.