Session: Undergraduate Research Posters: Green Chemistry & Sustainability:

Silicon is the most common material used in solar cells in part due to its abundance in the earth’s crust as well its intrinsic semiconductor properties. However, there are some drawbacks of silicon solar cells including toxicity in processing, difficulty in purification, high cost of fabrication, and rigidity. Materials used in bulk heterojunction organic photovoltaics (BHJ OPVs) have many advantages over silicon as they can be less expensive, have more tunable properties, and are flexible. Donor polymers for incorporation in OPVs made using furfural, an extract of corn stover, have the potential to be semi-sustainable. While furan polymers are less widely studied than their thiophene analogs, both heterocycles were studied in monomers for use in conjugated donor polymers. Two greener synthetic methods for monomer synthesis, mechanochemistry and microwave chemistry, were compared to traditional solution methods. A Knoevenagel condensation was carried out using an indole and an aldehyde employing the more toxic base piperidine as well as benign potassium carbonate. The products were characterized by ¹H-NMR, elemental analysis, X-ray crystallography, and electrospray mass spectrometry. Both of the greener methods gave higher yields and required less time than the traditional solution synthesis. NMR and elemental analysis of the products from both the mechanochemical and microwave reactions confirmed both condensation and further deprotonation of the indole N-H proton. This unexpected result is important because the next synthetic step to form our target monomer for the desired polymer is installing a long alkyl chain for polymer solubility. Current work focuses on the alkylation of the indole group of our monomer using these greener methods. Preliminary mass spectral results suggest alkylation of Knoevenagel products are possible via mechanochemistry and microwave chemistry.

Ted Pappenfus

Appearances