Catenated, Singlet Fission, and Semi-conducting Cyclic Polymers

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With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professors Adam S. Veige and Brent S. Sumerlin of University of Florida are developing new synthetic approaches for the preparation of functional conjugated polymers. Conjugated polymers are a unique class of polymers that contain long carbon chains with the repeating unit consisting of an olefin group bearing a carbon-carbon pi-bond. Such groups bring unsaturation to a chemical compound and are very commonly found in many natural products, such as cholesterol and fatty acids. In the case of conjugated polymers, when these pi-bonds are broken they create positive and negative charges along the polymer chain allowing them to conduct electricity. Since conjugated polymers contain tens of thousands of pi-bonds, their conductivity can sometimes surpass that of common metals such as copper or aluminum. In this research, a tungsten catalyst will first be used to prepare conjugated cyclic polymers which have the ability to interlock within themselves like beads on a string. These polymers will then be further modified synthetically in order to study and improve their optical and electronic properties. Polymeric materials prepared in this research have potential applications in the areas of molecular electronics and energy absorbing materials. The research activities associated with this award are also directed at broadening participation and enabling the training of high school, undergraduate, and graduate students in polymer chemistry. The outreach event “Halloween Molecular Mania” provides an attractive strategy to generate interest in science to participating high school students, local teachers and their parents.This project focuses on the use of tungsten-catalyzed ring expansion metathesis polymerization for the synthesis of various types of cyclic polymers. In the first goal, catenated (pi-bond interlocked) cyclic analogues of polyacetylene will be prepared and characterized. Special focus will be placed on detailed reaction kinetics and on the use of imaging (atomic force microscopy) and rheological studies to provide conclusive evidence of catenation. Induction of a long-lived singlet fission is to be achieved by attaching conjugated chromophores to cyclic polymers in the second goal. Singlet fission is a spin-allowed process, which could lead to long sought improved photo-conversion efficiencies with these linear pi-conjugated polymers. Lastly, the research team aims to achieve low barriers to configuration isomerization in the prepared cyclic polymers. This will be explored to synthesize semi-conducting cyclic polymers via an intramolecular pi-bond shift. This research has the potential to yield new knowledge in the area of cyclic polymers and provide mechanistic understanding for further catalyst design. Furthermore, access to semi-conducting cyclic polymers would provide important new opportunities to probe the fundamental principles of electrical conductivity in organic materials. This research also has the potential for long term scientific broader impacts on the fields of solar energy-harvesting and energy conversion.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.