Synthesis and characterization of cyclobutenedione-bithiophene π-conjugated polymers: acetal-protecting strategy for Kumada-Tamao-Corriu coupling polymerization between aryl bromide and Grignard reagents.

Cyclobutenedione is an aromatic ring that exhibits strong electron-withdrawing properties but is susceptible to undesired reactions with nucleophiles. Herein, Kumada-Tamao-Corriu coupling polymerization of a cyclobutenedione monomer whose carbonyl groups are protected as acetals was achieved. Hydrolysis of the acetals afforded donor-acceptor type π-conjugated polymers consisting of cyclobutenedione as an acceptor unit and bithiophene as a donor unit. The acetal-protected monomer was also subjected to Suzuki-Miyaura coupling polymerization. The absorption and emission spectra of the deprotected polymers shifted to the longer wavelength compared with the acetal-protected polymers.