Materials for Organic Electronics: Thiophene-based Low Bandgap Polymers by Claire Buysse
If you had asked me what I wanted to do with my chemistry degree a year ago, I wouldn’t have known. Even six months ago, I wasn’t completely sure where I was headed. I suppose that part of this uncertainty came from growing up in Marshall, a small town in southwest Minnesota which did not exactly provide me with much exposure to the broad range of careers I could pursue with chemistry. Nonetheless, I loved my hometown and took full advantage of the college chemistry courses my high school offered. I enjoyed and excelled in these courses, which led me to attend CSB/SJU last year and to take advantage of their up and coming chemistry program. It was at the College of St. Benedict that I discovered my passion for environmental topics and particularly my interest in solar energy. As a result of the encouragement and support of the chemistry faculty at CSB/SJU, I applied for this REU program – and I got in! I was so excited at the chance to do research this summer at North Dakota State University and I knew it would be an invaluable experience for me. Through this program, my eyes have been opened to all the opportunities that are available to me and I can truthfully say that it has been a phenomenal summer so far.
This summer, I am working in the Department of Chemistry at NDSU as a part of the Research on the Prairies REU program. I spend my time in the Rasmussen Research Lab under the supervision of Dr. Seth Rasmussen and graduate student Trent Anderson (pictured right). The focus of my lab group is on the creation of useful low bandgap polymers that have a variety of potential applications. The polymers of particular interest to us utilize conjugation and fused-ring systems, in addition to a number of other interrelated factors, to achieve low bandgap energies. This lower energy between valence and conduction bands (which closely corresponds to the HOMO-LUMO energy difference) allows the polymers to adopt electronic properties which mimic those of inorganic semiconductors. As a result, these organic materials have the potential to act in place of the inorganic electronic materials that are commonly used today. In particular, low bandgap polymers have been studied for use in organic solar cells (OPVs), organic light-emitting diodes (OLEDs), electrochromic devices, field-effect transistors, and more. Recently, these “flexible electronics” have attracted much attention for their low production costs and processibility. This new line of organic polymers also shows promise as a more sustainable source of electronic materials.
The chemical foundation for many of the low bandgap polymers in the Rasmussen Lab is thiophene, utilized for its versatility and ease of synthetic modification. Additionally, thiophene is an undesirable component of petroleum, which is typically removed during processing. The acquisition of the thiophene starting material from petroleum waste offers promise for a relatively sustainable (and essentially renewable) source of electronic material. In the early stages of my summer research experience, I used thiophene as the starting material in the synthesis of 2,3-dihexylthieno[3,4-b]pyrazine (later abbreviated as TP), which I completed in conjunction with my graduate student mentor. This synthesis involved a series of reactions and purification steps where I got the chance to apply many of the laboratory techniques I had worked with at St. Ben’s, in addition to learning some new techniques as well. Some of these included distillation, column chromatography, thin-layer chromatography, recrystallization, and extraction. Although the synthesis of TP has been well-established, completing this synthesis successfully gave me the chance to familiarize myself with the lab and to gradually increase my level of independence on the project.
The second part of my summer research experience dealt with the creation of a novel synthesis for a dimer of the TP I had synthesized and the 4-bromo-2,1,3-benzothiadiazole (or BTD) that my graduate student mentor had prepared. The first step towards this synthesis was the isolation of TP with a trimethylstannyl group bound in the 5 position, for which the synthesis had been previously recorded but an isolation of the compound was not attempted, likely due to instability and easy degradation. I completed this reaction a number of times and earned yields varying from 40-70%. At this point, my summer research experience was winding down and time constraints did not allow me to continue with my synthesis. As a result, future plans for this project in the Rasmussen group include the coupling of this compound with the brominated BTD to create the asymmetrical dimer as shown in the reaction below. Ideally, the electronic properties of this dimer would be characterized and the potential for a polymeric form of this dimer to be used as an organic electronic material evaluated.
Working in the Rasmussen Lab this summer has been an amazing experience for me and I am so glad that I have had this opportunity. I got the chance to work with some great people in the lab, and it turned out that one of them (Eric Uzelac, pictured here) went to St. John’s University with my brother and lived on the same freshman dorm floor! Spending ten weeks in Fargo for this program has definitely been a positive experience for me, both in and out of the laboratory. It was a blast to hang out with the other REU students, and a few of us even discovered a new hobby together at the climbing wall on campus. Ultimately, I’ve had a great time here at NDSU as a part of the Research on the Prairies program and I have discovered quite a bit about my interests in chemistry, too. I have a much better idea of where I’m headed in the future (grad school!) and what I want to do. So if you asked me what I want to do with my chemistry degree today, I’d know exactly the answer to give you.