Regiochemistry of poly(3-hexylthiophene): Synthesis and investigation of a conducting polymer

A series of experiments for undergraduate laboratory courses (e.g., organic, polymer, inorganic) have been developed. These experiments focus on understanding the regiochemistry of the conducting polymer poly(3- hexylthiophene) (P3HT). The substitution patterns in P3HTs control their conformational features, which, in turn, dictates the p conjugation and subsequent electronic properties of the materials. The regiochemistry in P3HTs can be controlled synthetically, and this experiment includes the synthesis of regioregular P3HT via Grignard metathesis chemistry. The regiochemistry is established unambiguously using techniques such as ¹H NMR and UV-vis spectroscopy;comparisons to the regiorandom isomer are then made. Density functional theory calculations are also used to shed light on the electronic and conformational features of the polymers by analyzing suitable oligomers. These experiments illustrate the importance of regiochemistry in organic materials and expose students to a number of important chemical concepts as well as useful physical and theoretical methods.