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.
