Materials Chemistry of Self-Assembling Dyes

有机染料在我们的环境中无处不在，针对特定技术的性能得到改善的新染料的需求不断增加。艾希霍恩集团开发的染料可以组装成特定的分子排列，类似于传统的液晶。这种在分子长度尺度(纳米结构)上对材料结构的控制对于染料膜和颗粒的性质的调整与染料本身的分子结构一样重要。在这一建议中，提出了有机染料的新设计标准：(1)自组装成芳香族基团之间具有强烈相互作用的各向异性材料；(2)形成具有特定纳米结构的单分子厚膜。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具有商业重要性的不同技术中的应用，如有机半导体、高压润滑剂、光学薄膜和传感器。主题1挑战了由更大的共轭/芳香结构组成的有机分子和聚合物的设计所需的柔性侧链的范式，因为这些刚性芳香结构否则是不溶的，很难加工。对侧链类型和它们的连接点的明智选择也被证明可以加强对这些分子在材料中的排列和排列的控制。然而，柔性侧链的使用有重要的缺点，因为它经常降低分子的热稳定性，排除某些纯化和处理方法(如升华)，不利于某些包装排列，并阻碍作为有机半导体的应用中的电荷传输。这项工作的主要目的是为可以加工成类似分子排列的侧链自由多环芳香族染料制定合理的分子设计标准，并确定优于含侧链类似物的材料性能。为主题2提出的研究建立在该小组最近在控制薄膜中染料分子在界面上的排列方面取得的成功的基础上。多环芳香族染料通常形成堆积分子的聚集体，并在界面上以边向取向自组装。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。它还会在表面产生一层相当致密的层，阻碍染料分子与环境中的分子(如分析物)和底物表面相互作用。艾希霍恩的团队开发了两亲染料，这种染料在界面上是平坦的，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，使其薄膜交联以增强稳定性，并展示它们在传感、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.