Conjugated Polymers Doped via Covalent Dopant-Molecule Adducts

With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professors Howard E. Katz and Paulette Clancy of the Johns Hopkins University are developing small organic molecules for use in doping of conjugated polymers. Conjugated polymers are carbon-based macromolecules that contain long chains consisting of alternating double and single bonds.

When the double bond arrangements are changed by removing or adding electrons, positive and negative charges are created in the polymers that enable them to conduct electricity similarly to metals such as copper. Currently, conjugated polymers are the most important class of materials used for optoelectronic devices such as LED (light-emitting diode) screens in mobile devices and computers; also being used to protect such electronic components from outside electrical interference.

In this research, systematic studies using a combination of experimental and computational approaches will closely examine the mechanism of electron transfer in these polymeric systems, a mechanism for which many details are still not known. Increased understanding of such systems has the potential to lead to novel conjugated materials with tunable electronic properties of relevance to flexible electronics and power devices.

The education and outreach activities of this project will focus on the engineering innovation program at Johns Hopkins University targeting low-income Baltimore City participants. A boot camp on coding will be offered to middle schoolers with the goal of improving the programming skills of future STEM (Science, Technology, Engineering and Math) scientists, with the particular goal of reaching women and members of underrepresented groups.

This research is targeting a series of thiophene-based molecules and oligomers for use in doping of conjugated polymers. The proposed theoretical and experimental studies are designed to test the hypothesis that the free energy change from (a) difference in hole/electron affinities, (b) work of charge separation, and (c) delocalization/distribution entropy between neutral conjugated polymers and covalent ion-adducts will lead to charge transfer and electrical conductivity.

Thiophene-based conjugated molecules and oligomers for adduct formation studies will be selected with a range of hardness/softness and to favor paired-electron, covalent bond formation (as opposed to electron transfer interactions) in aprotic solvents to enable testing of whether the covalent adducts ultimately serve as electron transfer agents of conjugated polymers. Extensive spectroscopic and electrochemical characterization methods are to be used to gain a deeper understanding of the doping mechanism and how structural changes affect doping levels, solid-state structures, conductivity, and the Seebeck coefficient.

The results associated with this research have the potential to lead to more reliable doping strategies in conjugated polymer- a key challenge for further development of organic bioelectronics and flexible conductors.

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.