Toward Defect Suppression in Polythiophenes Synthesized by Direct (Hetero)Arylation Polymerization

In this study, we have investigated different reaction conditions for defect suppression in polythiophene derivatives synthesized by direct (hetero)arylation polymerization (DHAP). The well-known PQT12 polymer was used as a model due to its simple structure which facilitated analysis. 2-Bromo-3,4′-didodecyl-2:2′,5′:2″,5″:2‴-quaterthiophene and 2-bromo-3″,4‴-didodecyl-2:2′,5′:2″,5″-2‴-quaterthiophene monomers allowed the analysis of both homocoupling defects and β-branching defects due to their asymmetric structure as well as the effect of β-protection. The properties of the resulting polymers were analyzed using size-exclusion chromatography, differential scanning calorimetry, UV–visible absorption spectroscopy, and 1H NMR spectrometry. Some model compounds were synthesized to help with end-groups analysis, revealing debromination as the main obstacle to chain growth. The highest quality polymer was obtained when using toluene as a solvent, Pd2dba3 as a palladium(0) catalyst, neo-decanoic acid (NDA) as a carboxylic acid additive, and a dual-ligand system with diamine TMEDA and phosphine P(o-OMePh)3. This study also revealed the importance of the choice of the monomers for the preparation of well-defined conjugated polymers.