Luminescent Main-Chain Organoborane Polymers: Highly Robust, Electron-Deficient Poly(oligothiophene borane)s via Stille Coupling Polymerization

A series of polymers (PBnT, n = 2–5) with boron atoms incorporated into the conjugated polythiophene main chain have been prepared via Pd-catalyzed coupling of stannylated thienylborane monomers. The polymers exhibit excellent long-term chemical stability to air and moisture and remarkable thermal stability with decomposition temperatures reaching over 300 °C. The high stability is achieved by placing very bulky pendant groups, 2,4,6-tri-tert-butylphenyl (Mes*) and 2,4,6-tris(trifluoromethyl)phenyl (FMes), on boron that prevent attack by nucleophiles. All these polymers display strong absorptions in the visible region and intense fluorescence in both solution and the solid state with quantum yields of up to 38% and fast radiative decay constants (kr) of up to 3.3 × 108 s–1. Density functional theory (DFT) studies on diborylated oligothiophene model compounds suggest that the strong absorption of the polymers results from π–π* transitions on the oligothiophene borane main chain with significant charge tran...