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

化学部的高分子、超分子和纳米化学项目支持 John D. Tovar 和 Arthur E. Bragg 教授的项目。托瓦尔和布拉格教授是约翰·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特性的新型导电塑料。 大多数电子设备都是由硅等非碳材料制造的。 含碳塑料更容易加工，可以制成轻质、大面积、甚至柔性的设备。这些塑料设备的应用范围从便携式光伏电池、发光显示器和可涂漆电子产品到新型生物相容性医疗材料。托瓦尔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，而布拉格的学生则学习使用激光研究和分析这些新型塑料的特性。两个小组之间的互动促进了化学和物理学思想的交叉融合。此次合作为从事该项目的学生提供了广泛的培训。托瓦尔和布拉格团体促进巴尔的摩市及其他地区的高中、本科生和研究生更多地接触化学研究。 各级代表性不足的少数族裔学生都参与了这项研究计划。该项目研究源自位于共轭主链主链上的可调芳香链段的π共轭低聚和聚合有机半导体。使用与苯、噻吩、吡咯等经典六π电子芳香核不同的非苯环芳香族结构单元。研究共轭聚合物中芳香性、扭转应变和无序的基本问题，目的是优化和调节所得的有效共轭长度。使用电子吸收和光致发光以及计算和电荷载体研究来测量共轭长度。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，从而能够根据所施加的光化学刺激快速有效地调节电子特性。这些聚合物的电性能通过光诱导开关事件前后的电测量进行评估，并使用复杂的超快激光光谱探测它们的电子结构，以捕获可能的短暂结构。 超快光谱用于表征其功能响应背后的光物理机制，并揭示它们如何依赖于分子结构。更广泛的影响包括向当地高中进行宣传，向他们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.