Design and Processing of Conjugated Polymers with High Charge Carrier Mobilities

非技术摘要：最近的研究表明，某些塑料的导电性比最初预期的要高得多。事实上，当引入晶体管设备时，这些塑料材料的导电性可以高于某些形式的常用硅。这样的发现为思考如何将塑料电子产品应用于广泛的应用开辟了新的选择，包括柔性太阳能电池、明亮的抗冲击手机显示屏，以及更节能的白色光源。然而，为了达到高水平的导电性，构成塑料材料的聚合物分子需要在两个重要的长度尺度上很好地组织起来。首先，形成聚合物链的分子单元必须以一种消除结构变化的方式连接起来。其次，聚合物链本身需要聚集在一起，这样它们才能包装成纳米级的纤维，然后这些纤维结合在一起形成导电膜。后者可以通过一个简单的程序来实现，该程序允许聚合物溶液在受控条件下在衬底上干燥。虽然这些进展是显著的，但有序聚合物的最大可能导电性仍然未知。因此，这项由美国国家科学基金会资助的计划的目标是研究新的聚合物结构的性质，这些结构旨在提高链条上的导电性，并促进分子的有效链间堆积。当溶液干涸时，将特别注意检查这些长分子如何相互关联，因为这个鲜为人知的过程决定了链之间的关系。该计划的成功完成将为科学和工程界提供新的指导方针，指导如何设计和加工应用于一系列新兴技术的新一代高导电塑料。技术摘要：该计划的核心是了解有机半导体中前所未有的高电荷载流子迁移率，这些有机半导体是基于引入晶体管设备的共轭聚合物。这些材料包括新的区域规则主链，富电子和贫电子杂环沿主链载体以严格交替的顺序排列。薄膜中聚合物链之间的高度有序配准也是一种要求，这种组织可以通过控制蒸发过程来实现。虽然这些发现有可能改变我们对如何利用塑料电子产品的看法，但对于如何获得如此高的迁移率以及这种运输的物理限制，仍存在很大差距。一个需要解决的重要问题是，分子量如何决定载体的迁移率，特别是因为载体的速度似乎是由沿聚合物链的运动主导的。将进行比平均分子量体系的制备和分级，并进行表征。还将设计、合成和测量定义明确的中间维度的模型化合物，以了解结构缺陷的可能作用，并深入了解链间接触的几何形状。这些材料将被整合到场效应晶体管设备中，以提取电荷迁移率的定量测量。这项工作的另一个重要方面涉及到努力详细说明具有高度共线聚合物链晶体的超分子结构的自组装和演化。还将制备含手性侧基的聚合物链。浓缩条件或低温导致这些形成聚集体，这些聚集体表现出强烈的圆二色信号，揭示了手性二级(例如，螺旋)结构的存在。这一简单的光谱工具将被用来了解分子结构的各个方面，以及底物和溶剂对从孤立的高分子链到高度有序的固态转变的影响。

NON-TECHNICAL SUMMARY:Recent studies have revealed that certain plastics can display electrical conductivity much higher than originally anticipated. Indeed, when introduced into transistor devices the conductivity of these plastic materials can be higher than certain forms of the commonly used silicon. Such a discovery opens new options for thinking about how plastic electronics can be utilized in a wide range of applications, including flexible solar cells, bright impact-resistant cellphone displays, and more energy-efficient white light sources. However, to reach high levels of electrical conductivity the polymer molecules that comprise the plastic material need to be very well organized across two important length scales. First, the molecular units that form the polymer chain have to be linked in a way that eliminates variations of structure. Second, the polymer chains themselves need to come together so that they pack into nanoscale fibers, which then coalesce to make up a conductive film. The latter can be achieved by a simple procedure that allows solutions of the polymer to dry on a substrate under controlled conditions. While these advances have been significant, the maximum possible conductivity of organized polymers remains unknown. The goals of this NSF-funded program are therefore to examine the properties of new polymer structures designed to increase electrical conductivity along the chain and to promote efficient interchain packing of molecules. Special attention will be paid to examine how these long molecules relate to each other as the solutions dry up, since this poorly understood process determines interchain relationships. Successful completion of the program will provide the scientific and engineering communities with new guidelines on how to design and process a new generation of highly conductive plastics for application in a range of emerging technologies.TECHNICAL SUMMARY: This program is centered on understanding unprecedented high charge-carrier mobilities in organic semiconductors based on conjugated polymers introduced into transistor devices. These materials comprise novel regioregular backbones with electron rich and electron poor heterocycles arranged along the backbone vector in a strict alternating sequence. Highly ordered registry between polymer chains in films is also a requirement, and this organization can be achieved via control of evaporation processes. While these findings have the potential of transforming our perspective of how to take advantage of plastic electronics, there are large gaps on how such high mobilities can be attained and the physical limits of this transport. One important question to address is how molecular weight determines carrier mobility, particularly because the carrier velocity appears to be dominated by motion along the polymer chain. Preparation and fractionation of specific average molecular weight systems will be carried out and subjected to characterization. Well-defined model compounds of intermediate dimensions will also be designed, synthesized and measured to understand the possible role of structural defects and to gain insight into the geometry of the interchain contacts. These materials will be incorporated into field-effect transistor devices to extract quantitative measures of charge mobility. Another important aspect of the work involves efforts to detail the self-assembly and evolution of the supramolecular structures with highly co-linear polymer chain crystals. Polymer chains with chiral side groups will also be prepared. Concentrated conditions or low temperatures lead these to form aggregates that exhibit strong circular-dichroism signals revealing the presence of chiral secondary (e.g., helical) structures. This simple spectroscopic tool will be used to understand the aspects of the molecular structure and the influence of substrate and solvent on the transition from isolated polymer chains to the highly ordered solid state.