CAREER: Understanding Charge Carriers in Mixed Ionic-Electronic Conducting Polymers using Ultrafast Near-Infrared Spectroscopy

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor Christopher Grieco of Auburn University will use advanced time-resolved spectroscopies to understand ion and charge carrier transport in conducting polymers. The motion of ions and charge carriers within polymers can be hindered due to complex molecular-level interactions and structural changes that are challenging to measure using traditional methods. Interactions between the charge carriers and near-infrared light, which triggers dynamics sensitive to their molecular environment, could be exploited as a sensor of ion and charge transport behavior. Using this concept, Professor Grieco and his students will perform ultrafast near-infrared laser spectroscopy experiments on conducting polymers under applied voltage to learn how ion and charge carrier transport is affected by the polymer's macromolecular structure. Their discoveries could lead to better conducting materials required for advancing electrochemical technologies from biosensors to flexible and lightweight electronics. The project will provide research opportunities for graduate and undergraduate students, as well as engage Alabamian students across multiple education levels through activities that aim to inspire and prepare students for careers in science and technology. This project will aim to develop a fundamental understanding of mixed ionic electronic conduction in conjugated polymers. The research will focus on probing polaron trapping in electrochemically active polymers using ultrafast near-infrared transient absorption spectroscopy. In this method, directly photoexciting polarons induces transient ion-polaron separation, leading to two key dynamical processes that report on their nanostructural environment and trapping. First, a transient Stark effect creates an electroabsorption signal that is sensitive to the electronic structure of surrounding polymer chains. Second, the picosecond re-equilibration kinetics of the ion-polaron pair report on trapping. In this project, experiments will be carried out to further develop this spectroscopy approach for probing polarons in working conducting polymer electrodes, and to elucidate how charge carrier dynamics can be controlled. Results could lead to chemical and structural design principles for enhancing mixed ionic-electronic conductivity in polymers to advance emerging technologies from flexible bioelectronics to electrochemical energy storage. The research concepts will also be integrated into multiple educational activities annually for middle-, high-school, and early undergraduate students, aiming to improve the Alabamian workforce in science and technology. 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.