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Main‐chain boron‐containing π‐conjugated polymers are attractive for organic electronic, sensing, and imaging applications. Alternating terthiophene‐borane polymers were prepared and the effects of regioisomeric attachment of the conjugated linker and variations in the electronic effect of the pendent aryl groups (2,4,6‐tri‐tert‐butylphenyl, Mes*; 2,4,6‐tris(trifluoromethyl)phenyl, FMes) examined. Pd₂dba₃/P(t‐Bu)₃‐catalyzed Stille polymerization of arylbis(2‐thienyl)borane and arylbis(3‐thienylborane) with 2,5‐bis(trimethylstannyl)thiophene at 120 °C gave polymers with appreciable molecular weight but MALDI‐TOF MS analyses showed evidence of unusually prominent homocoupling. These defects could be suppressed by using brominated rather than iodinated monomers, more hindered 2,5‐bis(tri‐n‐butylstannyl)thiophene as comonomer, and Pd₂dba₃/P(o‐tol)₃as the catalyst at 100 °C. Under these conditions, macrocyclic species withn=3–10 repeating units formed preferentially according to MALDI‐TOF MS analyses. Photophysical studies revealed a prominent effect of the regiochemistry and the nature of the pendent aryl groups on the absorption and emission, giving rise to orange, yellow‐green, blue‐green, and blue emissive materials respectively. The electronic effects were rationalized through DFT calculations on bis(terthiophene) model systems.

 

Conjugated polymers composed of tricoordinate boron and π-conjugated units possess extended conjugation with relatively low-lying LUMOs arising from p B –π interactions. However, donor–acceptor (D–A) polymers that feature triorganoboranes alternating with highly electron-rich donors remain scarce. We present here a new class of hybrid D–A polymers that combine electron-rich dithienosiloles or dithienogermoles with highly robust tricoordinate borane acceptors. Polymers of modest to high molecular weight are readily prepared by Pd-catalyzed Stille coupling reaction of bis(halothienyl)boranes and distannyldithienosiloles or -germoles. The polymers are obtained as dark red solids that are stable in air and soluble in common organic solvents. Long wavelength UV-vis absorptions at ca. 500–550 nm indicate effective π-conjugation and pronounced D–A interactions along the backbone. The emission maxima occur at wavelengths longer than 600 nm in solution and experience further shifts to lower energy with increasing solvent polarity, indicative of strong intramolecular charge transfer (ICT) character of the excited state. The powerful acceptor character of the borane comonomer units in the polymer structures is also evident from cyclic voltammetry (CV) analyses that reveal relatively low-lying LUMO levels of the polymers, enhancing the D–A interaction. Density functional theory (DFT) calculations on model oligomers further support these experimental observations.