Synthesis and Structure‐Property Relationships in Regioisomeric Alternating Borane‐Terthiophene Polymers

Abstract

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)3 as the catalyst at 100 °C. Under these conditions, macrocyclic species with n=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 Building Blocks Based on Electron-Deficient Thiaborin S-Oxides

“…These results demonstrate that these bulky aryl groups on boron can have a significant impact on the optical properties of small p-π* conjugated compounds. Indeed, extended conjugated systems such as p-π* conjugated polymers exhibit relatively high Φ PL values . This suggests that the molecular orbitals of the bulky aryl group on boron are not involved in the fluorescence process of the extended p-π conjugated system.…”