Rapid, facile synthesis of conjugated polymer zwitterions in ionic liquids

Abstract

Ionic liquids (ILs) were utilized for the rapid air-stable Suzuki polymerization of polar zwitterionic thiophene monomers, precluding the need for volatile organic solvents, phosphine ligands and phase transfer catalysts typically used in conjugated polymer synthesis. Ten different ILs were examined, demonstrating the scope and limitations of their utility as solvents in this Suzuki polymerization. Imidazolium, pyridinium and pyrrolidinium ILs proved effective for these polymerizations, with top performance achieved using pyrrolidinium triflate, affording polymers with molecular weight values >30 kDa. The enhanced solubility of these conjugated polymer zwitterions (CPZs) in ILs, relative to organic solvents, led to higher molecular weight polymers than obtained using previously reported methods. CPZs synthesized in ILs proved effective as cathode modification layers in solar cells, giving rise to a power conversion efficiency (PCE) of 7.57% in bulk heterojunction devices.