Regioregular poly(3-alkoxythiophene)s: Toward soluble, chiral conjugated polymers with a stable oxidized state

Chiral poly(3-(3,7-dimethyloetyloxy)thiophene)s were prepared using three different methodologies, rendering polymers with different degrees of regioregularity. In a first attempt, 3-alkoxythiophene was polymerized using FeCl3, resulting in a highly regioirregular poly(3-alkoxythiophene). Second, the GRIM methodology was applied, which yielded poly(3-alkoxythiophene)s with relatively high, but not perfect, degrees of regioregularity. Finally, an alternative methodology was used, which consisted of the exclusive formation and subsequent polymerization of 2-bromomagnesio-3-(3,7-dimethyloctyloxy)-5-bromothiophene) and which resulted in poly(3-alkoxythiophene)s with (almost) perfect regioregularity. The degrees of regioregularity were evaluated with H-1 NMR, UV-vis, and CD spectroscopy and cyclic voltammetry. These (regioregular) poly(3-alkoxythiophene)s show a very high lambda(max), indicating very high conjugation lengths. Moreover, the polymers could easily be oxidized and they were stable in both neutral as well as oxidized state. This stability can be correlated with the decrease in oxidation potential. The reproducibility and reversibility of the oxidation was demonstrated by UV-vis spectroscopy. Finally, the chiral properties of the polymers were investigated with circular dichroism spectroscopy. These experiments demonstrated again the difference in regioregularity of the polymers.