Regioregularity and properties of the poly(3-hexylthiophene) synthesized by palladium catalyzed direct CH arylation polycondensation under different reaction conditions

The effect of reaction conditions on Pd-catalyzed direct CH arylation polycondensation of 2-bromo-3-hexylthiophene to regioregular poly(3-hexylthiophene) (rr-P3HT) is exhibited. A wide range of reaction parameters, including palladium catalyst, ligand, reaction temperature and solvent, have been evaluated with a view to optimizing the polymerization conditions. For the first time, the end-groups of the synthesized polymer chains, confirmed by MALDI-TOF-MS measurement, were found to be significantly depended on the solvent used in reaction. Furthermore, homo-coupling and α or β coupling side-reactions were detected in a model oligomer synthesis reaction, which was supposed to be the reason for the low regioregularity of the resulting P3HT. Optical and electrochemical properties, as well as photovoltaic performance of the synthesized P3HT were investigated.