Fluxional macromolecular pi-electronics via rational manipulation of aromaticity and spin

化学部的大分子、超分子和纳米化学项目支持John D. Tovar和Arthur E. Bragg教授的项目。Tovar教授和Bragg教授是约翰霍普金斯大学化学系的教员。他们正在开发具有可调节电子性能的新型导电塑料。大多数电子设备都是用硅等非碳材料制造的。含碳塑料更容易加工，可以制成重量轻、面积大、甚至灵活的设备。这些塑料设备的应用范围从便携式光伏电池，发光显示器和可涂电子产品到新的生物相容性医疗材料。Tovar教授小组的研究人员在电子活性塑料的设计和构造方面获得了宝贵的培训，而Bragg的学生则学习使用激光调查和分析这些新塑料的特性。这两个小组之间的相互作用促进了化学和物理思想的交流。这项合作为从事该项目的学生提供了广泛的培训。Tovar和Bragg小组促进了巴尔的摩市内外高中、本科和研究生水平的学生更多地接触化学研究。各级少数族裔学生都参加了这个研究项目。本项目研究π共轭低聚物和聚合物有机半导体，这些半导体是由共轭主链主链上的可调芳香段衍生而来的。非苯类芳香族结构单元，与苯、噻吩、吡咯等的经典六电子芳香族核不同。研究了共轭聚合物的芳香性、扭转应变和无序性等基本问题，旨在优化和调节共轭聚合物的有效长度。利用电子吸收和光致发光，结合计算和载流子研究，测量了共轭长度。提出了一种新的聚合物设计，将光化学开关事件与聚合物大分子构象变化解耦，从而实现了作为应用光化学刺激函数的电子特性的快速有效调谐。这些聚合物的电性能是通过光诱导开关事件前后的电测量来评估的，它们的电子结构是用复杂的超快速激光光谱来探测的，以便捕捉可能的稍纵即逝的结构。超快光谱学用于表征其功能响应背后的光物理机制，并揭示这些机制如何依赖于分子结构。更广泛的影响包括向当地高中介绍电子材料的特性。

The Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division supports the project by Professors John D. Tovar and Arthur E. Bragg. Professors Tovar and Bragg are faculty members in the Department of Chemistry at Johns Hopkins University. They are developing new electrically conductive plastics with adjustable electronic properties. Most electronic devices are manufactured from non-carbon materials such as silicon. Carbon-containing plastics are much easier to process, allowing them to be fashioned into lightweight, large area, and even flexible devices. Applications for these plastic devices range from portable photovoltaic cells, light-emitting displays and paintable electronics to new biocompatible medical materials. Researchers working in Professor Tovar's group gain valuable training in the design and construction of electronically active plastics, while Bragg's students learn to investigate and analyze the properties of these new plastics using lasers. The interaction between the two groups fosters cross-fertilization of ideas in chemistry and physics. The collaboration provides broad training to students working on this project. The Tovar and Bragg groups promote increased exposure to chemistry research among high school, undergraduate and graduate-level students within Baltimore City and beyond. Underrepresented minority students at all levels participate in this research program. This project investigates pi-conjugated oligomeric and polymeric organic semiconductors that are derived from tunable aromatic segments positioned along the conjugated main chain backbone. Non-benzenoid aromatic building blocks that depart from the classical six pi-electron aromatic nuclei of benzene, thiophene, pyrrole, etc. are used. Fundamental issues of aromaticity, torsional strain and disorder in conjugated polymers are investigated with the goal to optimize and regulate the resulting effective conjugation lengths. The conjugation lengths are measured using electronic absorption and photoluminescence, coupled with computational and charge carrier studies. A new polymer design is proposed that decouples the photochemical switching event from polymer macromolecular conformational changes, thereby enabling rapid and efficient tuning of electronic properties as a function of an applied photochemical stimulus. Electrical properties of these polymers are assessed through electrical measurements before and after photoinduced switching events, and their electronic structures are probed using sophisticated ultra-fast laser spectroscopy in order to capture possible fleeting structures. The ultra-fast spectroscopy is used to characterize photophysical mechanisms underlying their functional responses and to unravel how these depend on molecular structure. The broader impacts include outreach to local high schools to introduce them to the properties of electronic materials.