Control and Characterization of the Morphology and Photophysics of Conjugated Molecules in Isolation and in Aggregate

聚合物是由数百或数千个分子组成的长链，称为单体。当许多聚合物链聚集在一起时，它们形成塑料，其性能取决于单体的化学结构。虽然有些聚合物是硬的或柔性的，但另一些聚合物的设计是为了吸收光，传输激发态能量(称为激子)，并导电，从而产生薄、轻和灵活的电子器件。虽然这种聚合物已经知道一段时间了，但设计出与传统电子材料(如硅)具有相同性能的材料是困难的。激子在聚合物中的运动既包括沿着单链的运动，也包括链之间的转移，研究这种链间跳跃是一个挑战。在化学系大分子、超分子和纳米化学项目的资助下，哥伦比亚大学的劳拉·考夫曼教授正在使用复杂的显微镜来研究激子在聚合物聚集体中的流动。从该项目中获得的见解可能有助于为廉价的太阳能电池和柔性电子产品铺平道路，这将产生显著的社会效益。该项目还为即将进入国家科学技术大军的研究生和本科生提供培训机会，考夫曼教授和她的学生正在与当地小学生接触，以提高他们对科学探索和发现的兴趣。该项目正在探索单个聚合物链的激发态性质，以及作为聚集体组织在一起的聚合物。重点介绍了多荧烯、均二亚胺和聚并苯，每一种都有很好的光电子学应用前景。考夫曼教授和她的学生使用她实验室最近开发的方法，通过改变溶剂混合物和溶胀来控制单个聚合物链组装成特定大小和结构的聚集体。不同堆积密度的聚集体的制备是通过仔细选择分子性质和调整由Ostwald成熟或合并驱动的聚集体来完成的。光谱性质(如吸收、发射、各向异性)是利用偏振调制和超分辨显微镜在逐个生色团的基础上进行表征的，这提供了聚合物构象和激发态光物理性质之间的关联的详细图像。通过控制聚集体的形成和详细的光谱测量相结合，研究小组试图确定介观长度尺度上的形态排序是否可以用于调整激子扩散长度和聚集体的其他光物理特性。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Polymers are long chains of hundreds or thousands of molecules, called monomers. When many polymer chains are aggregated together they form plastics, whose properties depend on the monomer's chemical structure. While some polymers are made to be stiff or flexible, others are designed to absorb light, transport excited state energy (called excitons), and conduct electricity, giving rise to electronic devices that are thin, light, and flexible. While such polymers have been known for some time, designing materials that have the same performance as traditional electronics materials (e.g. silicon) is difficult. The movement of excitons through a polymer involves both motion along a single chain, as well as transfer between chains, and studying this interchain hopping is a challenge. With funding from the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Laura Kaufman at Columbia University is using sophisticated microscopies to study the flow of excitons through polymer aggregates. The insights gained from the project could help pave the way to inexpensive solar cells and flexible electronics, which would have significant societal benefits. The project is also providing training opportunities for graduate and undergraduate students, who will enter the Nation's science and technology workforce, and Professor Kaufman and her students are engaging with local elementary school students to promote interest in scientific exploration and discovery. The project is exploring the excited state properties of individual polymer chains, as well as polymers that are organized together as aggregates. The focus is on polyfluorenes, perylene diimides, and polyacenes, each of which are promising for optoelectronic applications. Professor Kaufman and her students use approaches recently developed in her laboratory to control the assembly of single polymer chains into aggregates of particular size and structure through variation in solvent mixture and swelling. Preparation of aggregates of different packing densities is accomplished by careful selection of molecular properties and by tuning the aggregation to be driven by Ostwald ripening or coalescence. Spectroscopic properties (e.g. absorption, emission, anisotropy) are characterized on chromophore-by-chromophore basis using polarization modulation and super-resolution microscopies, which provide a detailed picture of the correlation between polymer conformation and excited state photophysical properties. Through the combination of controlled aggregate formation and detailed spectroscopic measurement, the research team is attempting to ascertain whether morphological ordering on mesoscopic length scales can be used to tune exciton diffusion length and other photophysical characteristics of aggregates.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.