Mutual Synthesis of Conjugated Polymers and Dopants for Well-Ordered Self-Assemblies

该奖项由化学系的高分子、超分子和纳米化学项目资助。约翰·霍普金斯大学的霍华德·E·卡茨教授探索了导电塑料的主要成分--聚合物材料和掺杂剂--可以同时设计以获得最佳性能的想法。这需要它们分子大小的亚基很好地结合在一起，创造出连续的导电路径，并且掺杂剂保持它们稳定导电时移动的电荷的能力。一个需要探索的根本问题是，掺杂剂在整个塑料体积中均匀混合是更好，还是混合物的不同部分富含塑料而其他部分富含掺杂剂更好。制造塑料和掺杂剂的新方法，更详细地了解它们如何结合在一起并促进塑料混合物中的导电，以及在制造塑料之前预测塑料性能的基于计算机的模型，都是该项目的预期成果。导电塑料是许多新兴技术的基础，例如用于更有效地利用能源的塑料太阳能电池和光发射器、对国防行动重要的危险化学品的探测器，以及用于检测疾病的医疗设备。所有这些技术都创造了新的经济机会。将研究与教育和推广相结合，将研究生培养为未来塑料电子劳动力的成员，并为巴尔的摩市的小学、高中和艺术学院的学生带来塑料电子的机会。该项目的主要目标是设计和合成一对共轭的、高载流子迁移率的聚合物和相应的化学掺杂剂，这些聚合物可以在这些聚合物中诱导电荷，从而使这些对形成保持良好的电荷传输分子组织的组件。原始聚合物的超分子结构是共轭聚合物主链之间的pi相互作用和烷基侧链造成的规则间距的结果。我们的想法是探索聚合物和掺杂剂成分中不同的化学设计元素，以便掺杂剂能够适应超分子结构，甚至增强结构。将这些设计策略与掺杂剂共价连接到主链上的极端情况进行比较，这些掺杂剂被称为“自掺杂聚合物”，而掺杂剂有望从电荷传输聚合物中分离出来，从而存在于不同的区域中。用X射线和中子散射技术阐明了聚合物-掺杂剂组装的分子堆积。吸光度、光电子和电子自旋共振光谱表明电荷载流子的形成。计算模型为堆积效率和电荷转移效率提供了理论基础。该项目的成果指导了聚合物的设计，这种聚合物只使用电子或空穴作为电荷载体，而不使用离子贡献，以高效的方式导电。该项目可能解决这样的不确定性，即具有掺杂官能团的结构是否毗邻主链或远离主链导致更好的定义结晶度和更高的电子传导性。为今后的设计提供了各种装配类型选择的理论依据。由于聚合物是从与掺杂剂的混合物中组装而来的，因此掺杂剂浓度是可调节的，以实现最大的导电性，或者用于优化其他功能，例如向光电设备或热电复合材料的基质中注入电荷。

This award is funded by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry. Professor Howard E. Katz of Johns Hopkins University is supported to explore the idea that the main components of conducting plastics - the polymeric material and the dopants -- can be designed simultaneously for best performance. This requires that their molecule-sized subunits fit well together, continuous paths for conducting electricity are created, and the dopants maintain their ability to stabilize the electrical charges that move when the electricity is conducted. A fundamental issue to be explored is whether it is better for dopants to be mixed equally through the entire volume of the plastics, or whether it is better for separate parts of a mixture to be rich in the plastic and others be rich in the dopant. New ways to make plastics and dopants, more detailed understanding of how they fit together and promote electrical conduction in the plastic mixtures, and computer-based models for predicting the properties of the plastics in advance of making them are expected outcomes of this project. Conducting plastics are the basis of numerous emerging technologies such as plastic solar cells and light emitters for more efficient use of energy, detectors for dangerous chemicals important for defense operations, and medical devices to detect diseases. All of these technologies have created new economic opportunities. Integrating the research with education and outreach trains graduate students as future members of the plastic electronics workforce, and brings the opportunities of plastic electronics to elementary school, high school, and art institute students in the City of Baltimore. The main objective of this project is to design and synthesize pairs of conjugated, high-charge-carrier-mobility polymers and corresponding chemical dopants that induce charges in those polymers, such that the pairs form assemblies that retain favorable charge-transporting molecular organization. The supramolecular structure of the original polymer is a consequence of pi-interactions among the conjugated polymer main chains and regular spacing caused by alkyl side chains. The idea is to explore different chemical design elements in the polymer and dopant components so that the dopants become accommodated in the supramolecular structure, or even enhance the structure. These design strategies are compared to the extreme cases of dopants covalently attached to main chains, known as "self-doped polymers", and dopants that would be expected to phase segregate from the charge-transporting polymers and thus exist in separate domains. The molecular packing of the polymer-dopant assemblies is elucidated using x-ray and neutron scattering techniques. Absorbance, photoelectron, and electron spin resonance spectroscopy indicate the formation of charge carriers. Computational modeling creates a theoretical basis for both the packing and charge transfer efficiency. The outcome of this project guides the design of polymers that conduct electricity with high efficiency using only electrons or holes as charge carriers, without ionic contributions. The project may resolve the uncertainty about whether structures with dopant functionality adjacent to main chains or remote from main chains lead to better defined crystallinity and higher electronic conductivity. A theoretical basis for selecting among various assembly types for future designs is developed. Because the polymers are assembled from blends with dopants, the dopant concentration is tunable for the maximum conductivity, or alternatively for optimization of other functions such as charge injection into optoelectronic devices or matrices for thermoelectric composites.