In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Kenneth Carter of the University of Massachusetts, Amherst will develop methodologies to form n- and p-type doped conjugated poly(ionomer)s from a single, neutral parent polymer. The approach is to synthesize conjugated polymers possessing benzimidazole repeat units either in homopolymer or copolymer form; to probe how acid-base and alkylation chemistries can be used to switch the benzimidazole repeat unit between various types of aromatic systems; to study systematically the effects of these modifications on the electrical and photo-physical behavior of the polymers; and to explore how these polymers can be used to fabricate functional organic electronic devices. The broader impacts involve training graduate and undergraduate students in polymer chemistry and organic electronics science, disseminating research results and concepts via publications, presentations at conferences and incorporation of material into lecture courses, and broadening the participation of underrepresented groups in chemical sciences via partnering with NOBCChE to bring undergraduates to campus for summer research experiences.
Plastics are long chain organic molecules and are found in many facets of everyday life, including food packaging, structural materials for automotive and aerospace transportation, and lightweight electronic devices. Electrically conducting carbon-based (organic) molecules and polymers hold enormous promise for realizing highly efficient, affordable, and broadly available electronic and optical devices. This research explores how chemistry can be used to control and switch the electronic properties of an electrically conducting polymer. Ultimately, such work could lead to the development of organic electronic materials, low cost solar cells, light emitting displays, and chemical and biological sensors.
There were two main scientific thrusts of this two-year project: (1) to synthesize a new class of neutral conjugated polymers which can be easily converted into cationic or anionic poly(ionomer)s; (2) systematically study the effects of these modifications with respect to their processability and the influence of charge on the electrical and photo-physical behavior of the polymers. In summary, we have been highly successful in achieving results towards our program goals. We are leaders in the research of semiconducting polymers. A large number of new materials have been synthesized. The work performed in this reporting period is helping us understand the basic properties of these new polyionomers and their neutral benzimidazole-based precursors. Through the incorporation of 4,7-benzimidazole moieties in poly(fluorene) semiconducting polymer systems, we demonstrated the feasibility of a dually-dopable polymeric system. By the addition of simple acidic or basic reagents, the neutral polymer was effectively doped in solution, yielding stable doped species. The neutral polymers, as well as both the n-doped and p?doped derivatives, were soluble in suitable solvents and could be processed into thin films. The non-optimized systems showed the potential for reversibly and systemically manipulating band-gaps of a single polymeric species through post-polymerization chemical methods. This ability to control the electronic band-structure is unmatched by current synthetic techniques which require synthesis of distinct macromolecules to achieve alternate band structures. With the demonstration of their dopability, we believe that these semiconducting 4,7?benzimidazole-based materials represent an important evolution in the progress of conjugated polymers and will offer the exciting possibility of tunable control over hole and electron transporting behavior of these materials in device applications. The project has directly supported one UMass PSE graduate who is now entering his third year of graduate study (Mr. Andrew Davis). The project has also enabled the training of two undergraduate researchers (Carmin Fisher and Cathrin Müller) who performed their thesis research on this project and they have gained an excellent education and training on advanced polymeric materials. We have also had the part-time assistance of two postdoctoral scientists (Dr. Charlotte Mallet and Fatma Koyuncu). Four of these five people working on this project are female. Two additional students are currently directly supported by this project and they are gaining an excellent education and training on advanced polymeric materials. Other group members and university department researchers also benefit from the program in terms of access to new materials, fabrication facilities, equipment and associated training. The project has spawned two new international collaborations, one with Professor Hans-Werner Schmidt at the Universität Bayreuth and the other with Dr. Fatma Koyuncu and Dr. Sermet Koyuncu at Çanakkale Onsekiz Mart University (Turkey). The PI and students are active in outreach activities ranging from K-12 education, mentoring and career development of under-represented minority and women scientist, local Science Cafes, and industrial outreach through the UMass CUMIRP program. The first presentation of our findings was presented at the Fall 2013 MRS meeting in Boston MA. A publication in Macromolecules has appeared "Synthesis and Characterization of Poly(2-alkylbenzimidazole-alt-9,9-dihexylfluorene)s: A Dually Dopable Polymer System", Harris, J. D., Mallet, C.; Müller, C.; Fischer, C.; Carter, K. R.*, Macromolecules, 2014, 47(9), 2915-2920. DOI: 10.1021/ma500231n). Two other manuscripts are currently in preparation.