Polymers are long molecular chains formed by linking together many small molecules, called monomers. By varying the monomer's chemical structure, chemists can create polymers that absorb light, fluoresce, and conduct electricity, making them useful for cell phone displays, solar photovoltaics, and even in medical imaging. Despite these advantages, polymers degrade upon exposure to oxygen and light, and their fluorescence decreases when the chains pack together to form the films used in devices. With support from the Chemical Structure, Dynamics, and Mechanism A and Macromolecular, Supramolecular, and Nanochemistry Programs in the Division of Chemistry, Professor Linda Peteanu of Carnegie-Mellon University is addressing these challenges. Working with her students, she is using a wide array of spectroscopic tools to understand why polymer chains degrade less when placed onto metal films, as well as why their fluorescence is reduced when the chains pack together. The team's discoveries are helping chemists to create improved polymers for consumer electronics applications, which could have significant societal broader impact. The educational broader impacts lie in the training of students with expertise in optics and novel imaging methods. In addition, outreach to K-12 students and to the public demonstrate how light interacts with matter. The outreach activities and demonstrations developed as part of this award help young scientists visualize the connections between the microscopic and macroscopic worlds and help the general public appreciate how this fundamental connection has been critical in the development of many of the products they use in their everyday lives.
This research focuses on conjugated semi-conducting oligomers, polymers and their aggregates. These materials demonstrate the remarkable ability to transport energy and charge over distances that are large compared to molecular scales. These properties, in addition to their emissivity, are important to applications ranging from opto-electronic devices, such as photovoltaics and light emitting diodes, to chemical sensors and biological labels. From a fundamental perspective, extended or electronically-delocalized structures, such as these polymers and their aggregates, are of interest because their electronic properties lie in the gap between those of small molecules and extended solids. The goals of this project are two-fold. The first is to perform a comprehensive investigation utilizing a variety of spectroscopic and imaging tools, molecular modeling, and synthetic modification to understand how the emission spectra, dynamics and yields are controlled by ground-state conformation and by the rates and efficiencies of intersystem crossing and internal conversion. The second is to explore the effects of two local environmental perturbations, solvent polarity and plasmonic field effects, on the fluorescence yield and the rates and efficiencies of singlet-triplet relaxation, energy transfer and charge separation. These data may yield a better understanding of how the structure, morphology, and local environment of this important class of materials can be optimized for existing and novel applications that require high emissivity and efficient charge transport.
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.
