Experimental and theoretical insights into the unique oxidative polymerization mechanism of N-alkylaminothiophenes.

摘要

A number of conjugated polymer systems can be generated via electropolymerization, including polythiophenes and polyanilines. While both have been reported to polymerize anodically via radical coupling, the presence of the aniline nitrogen plays a significant role in the electropolymerization mechanism. Initial studies of 3-(N-alkylamino)thiophenes, structural hybrids of thiophene and aniline, revealed that electropolymerization occurs at significantly reduced potentials compared to other 3-substituted thiophenes. This suggested that such aminothiophenes may electropolymerize via a mechanism that differs from that reported for typical thiophenes. In this study, the electropolymerization mechanism of N-alkylaminothiophenes is studied utilizing experimental and theoretical methods. Synthesis of new short chain N-alkylaminothiophenes is discussed, and an electropolymerization mechanism is proposed whereby oxidation occurs through removal of a nitrogen lone pair electron, followed by a chemical step resulting in radical contribution on the thiophene ring through resonance. Coupling of two radical cations followed by deprotonation forms the dimeric species, with further oxidation and coupling steps forming polymers through a chain-growth process. As polythiophenes with redox active side chains continue to be developed, further understanding of their effect on the polymerization mechanisms will be critical when designing these new materials.