Side-Chain Driven Assembly of Polymer Semiconductors

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With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Prof. Natalie Stingelin and Dr. Anna M. Österholm of Georgia Institute of Technology are studying fundamental processes that underlie the assembly of polymer semiconductors. The local arrangements of these long chain macromolecules dictate important photophysical, electronic and electrochemical processes in this broad class of materials. All of these processes are important in a range of optoelectronic device platforms, such as LED (light-emitted) screens, wearable electronics, and even bioelectronics. In this research, semiconducting polymers will be prepared in which the main polymer backbone is decorated with side-chains of different lengths, densities, and polarity. Optoelectronic properties will then be investigated to gain further understanding on how they depend on side-chain arrangement and subsequent backbone ordering. As opposed to conventional synthetic approaches, this research will use electricity and blending with surfactants to manipulate and control side-chain assembly. Relevant physical processes associated with polymer dynamics will be investigated using a plethora of sophisticated experimental tools. They include linear and vibrational spectroscopies, thermal analysis, and electrochemical measurements that allow for rapid evaluation of polymer assembly motifs. This project will create a highly multidisciplinary and diverse research and education environment for students where they will be exposed to academic and industrial perspectives, national laboratories, as well as national and international collaborators. The research team will also partner with the Georgia Tech’s Center for Organic Photonics and Electronics, the Georgia Tech Polymer Network, and groups such as Women in Materials Science and Engineering (WiMSE) and Women in Chemistry (WiC) to develop a set of diversity-supported programs focusing on preparing underrepresented minorities for faculty positions. This research aims to provide fundamental insights of the physics underlying the assembly of polymer semiconductors, focusing on answering the question of what role side-chain design plays in dictating backbone order/disorder. Particular emphasis is placed on the use of electrochemical and physicochemical approaches to control the side-chain interactions and subsequent backbone order in various polydioxythiophenes to deliver an assembly framework that exploits the sidechain arrangement for dictating backbone ordering. Side-chain motifs that promote supramolecular assembly in neat polymer semiconductor systems into solid-state structures with little backbone distortion will first be identified with a strong emphasis on chemical structure, side-chain branching point location, and side-chain density. Electrochemical doping will then be utilized to investigate changes in polymer assemblies and how they influence both redox and charge transport properties. Lastly, small molecule additives will be blended with a polymer semiconductor to examine their effect on backbone conformation. This research will address fundamental questions in the field of conjugated polymers through extrinsic approaches rather than the synthetic ones. If successful, the proposed work will have a major impact on the semiconducting polymer field, particularly optoelectronic device platforms, such as organic light-emitting diodes, organic photovoltaics, organic field-effect transistors, as well as emerging technologies for bioelectronics and neuromorphic sensing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.