CAS: Synthesis, Assembly and Photophysical Behaviors of Nonconventional Purine-Containing Conjugated Copolymers

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

With the support of the Macromolecular, Supramolecular and Nanochemistry (MSN) program in the Division of Chemistry, Michael S. Kilbey and Brian K. Long of the University of Tennessee, Knoxville are developing conductive purine-containing copolymers. Purines are aromatic compounds that contain two rings fused together. They are the most widely occurring nitrogen-containing heterocycles in nature and are common building blocks found in DNA and RNA. Other purine sources include meats, yeast, oatmeal and caffeine. In this project, small molecule chemistry will first be performed based on conventional coupling reactions in order to understand site reactivity of purine-containing monomers. The knowledge gained will then be used to couple these monomers with sulfur-containing heterocycles to prepare well-defined oligomers and fully conjugated copolymers. The copolymers will be examined for their ability to conduct electricity and emit light, making them potential candidates for optoelectronic devices or for imaging and sensing applications. A suite of photophysical and structural characterizations will also be performed to generate relationships that quantify how connectivity and regiochemistry affect self-assembly in solution and in the solid state, as well as how they influence photophysical properties. The resulting body of fundamental chemistry knowledge has the potential to spur innovations in the design and synthesis of conjugated polymers from nonconventional building blocks based on purines. Education and training will be promoted through co-advising of graduate students and the development and implementation of graduate student mentoring program. Additionally, students from underrepresented groups in research will be involved through established NSF-supported on-campus programs. Engagement with young learners and the greater public through service to the Tennessee Science Olympiad will promote and nurture interests of young learners in science. This work will investigate the role of molecular design on the conformation, organization and properties of well-defined oligomers and fully conjugated purine-containing polymers. In the first objective, small molecule coupling studies will be used to investigate reactivity bias of the sites used for carbon-carbon bond formation on the thiophene-purine-thiophene (TPT) triads. These studies are expected to provide critical insights into how purine-containing copolymers are constructed and, in this way, inform efforts to create well-defined purine-containing oligomers and copolymers. The second objective will focus on the synthesis and characterization of trimers with defined patterns of connectivity across the purine scaffold (2,6-, 6,8-, and 2,8-connectivity), but featuring systematic variation in regiochemistry. Finally, in the last objective, linearly conjugated and cross-conjugated purine-thiophene copolymers will be synthesized via direct (hetero)arylation polymerization of TPT triads using either AB polymerizations or AA+BB copolymerizations. Outcomes from this research program are anticipated to inform and stimulate efforts to use molecular design to modulate nanoscale assembly and properties of conjugated polymers, which find applicability in various contexts due to their functionality as organic semiconductors. In addition to advancing a molecular engineering approach to understand behaviors and properties of novel, functional polymers, this work has the potential to provide fundamental knowledge that expands the potential of bio-derived and abundant purines in organic electronics. 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.