A New Design Paradigm in Low Band Gap Conjugated Polymers

North Dakota State University Fargo, Fargo ND

Investigators

Abstract

With this award, the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry is funding Professor Seth C. Rasmussen of the Department of Chemistry and Biochemistry at North Dakota State University to advance fundamental understanding of structure-function relationships in conjugated polymers. Conjugated polymers are long chain, organic molecules. Much like traditional semiconductors such as silicon, these polymers can become conductive when one applies a voltage (such as in transistors) or light (such as in solar cells). This team creates design strategies for constructing new types of conjugated polymers with potential applications in organic electronics, photovoltaics and organic light-emitting diodes. In addition to conventional synthetic techniques, computational modelling is used to evaluate potential polymer structures and to predict their electronic properties. The broader activities associated with this research focus on outreach to Native American colleges via the university’s NATURE program. The team also contributes to the history of polymer science and technology via the documentation and dissemination of new historical publications on the origin and growth of conjugated polymers. This research is focused on advancing understanding of structure-function relationships in conjugated polymers, in particular the role of donor-acceptor interactions in efforts to produce reduced band gap (Eg=1.5-2.0 eV) and low band gap (Eg<1.5 eV) polymers. The band gap is a critical parameter of organic semiconducting materials, particularly for their application in electrochromic devices, organic photovoltaics, organic light-emitting diodes, and NIR photodetectors. Of particular focus here is the application of a new design paradigm that pairs conventional acceptor units with thieno[3,4-b]pyrazine building blocks. These building block act simultaneously as very strong acceptors and very strong donors. The preparation of the conjugated polymers is accomplished using direct arylation polymerizations. Computational techniques aid in experimental design, predicting desired electronic properties. This new design paradigm is applied to other monomers such as acenaphtho[1,2-b]thieno[3,4-e]pyrazine, dibenzo[f,h]thieno[3,4-b]quinoxaline and thieno[3',4':5,6]pyrazino[2,3-f][1,10]phenanthroline, and some of the materials are tested in devices via established collaborations. This research addresses the fundamental design principle for conjugated polymers involving two separate acceptors. The chemistry is transformative with a strong potential to advance fundamental understanding of conjugated polymer design, especially in terms of the design of low band gap, n-type, and ambipolar polymers. 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.