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

Abstract

The functionalization of polythiophene with dimesitylborane π-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 (DP_n) 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.