ipso-Arylative Ring-Opening Polymerization as a Route to Electron-Deficient Conjugated Polymers

ipso-Arylative ring-opening polymerization of 2-bromo-8-aryl-8H-indeno[2,1-b]thiophen-8-ol monomers proceeds to M_n up to 9 kg mol⁻¹ with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2-benzoylphenyl or 2-(4-hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=−5.9/−4.0 eV) than poly(3-hexylthiophene) owing to the electron-withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10⁻³ cm² V⁻¹ s⁻¹) for poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10⁻⁶ cm² V⁻¹ s⁻¹), which suggests such polymers are candidates for n-type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side-chain steric interactions could be a key factor influencing charge mobilities.