Conjugated alternating copolymers with 4,4′-dimesitylboryl-2,2′-bithiophene as a building block

The functionalization of polythiophene with dimesitylborane pi-acceptor groups has a strong effect on the conjugated polymer backbone, resulting in interesting optical and electronic properties. To investigate the interplay between the electron-deficient organoborane substituents and the conjugated polymer main chain, a series of alternating copolymers was prepared. Several aromatic building blocks that are commonly used in organic semiconductors, i.e. fluorene, carbazole, and triphenylamine, were chosen as comonomers for combination with 4,4'-diboryl-2,2'-bithiophene units. First, the trimethylsilyl-substituted copolymers PFT-Si, PCT-Si, and PTT-Si were prepared via standard Suzuki coupling reaction of 5,5'-diiodo-4,4'-bis(trimethylsilyl)-2,2'-bithiophene and the respective pinacolborane-functionalized aromatic comonomer. Subsequent post-polymerization modification reactions, which involved treatment with BBr3 and then mesitylcopper, led to three borylated copolymers, PFT-B, PCT-B, and PTT-B. The degrees of polymerization (DPn) and the polydispersities are consistent with those of the silylated precursor polymers. The photophysical and electrochemical properties of these new polymers have been studied in detail.