Fabrication of conjugated polymers with benzofuran unit based on I2- catalyzed intramolecular cyclization of polyphenylacetylene

The polyphenylene ethynylene P1 and P2 were synthesized by Sonogashira coupling reaction. In the presence of electrophilic reagent I2, benzyne group was cyclized with ortho-methoxyl group to form benzofuran by the removal of methyl group, resulting in the benzofuran-containing conjugated polymers CP1 and CP2. The different reaction conditions have obvious effects on the cyclization rate, and the optimization reaction conditions are: Chloroform as the reaction solvent, the concentration of polymer P is 2.1-2.2 mg/mL, 40-50°C, and the cyclization rate raises with the increasing of the amount of catalyst I2 or extending reaction time. The solubility of CP1 and CP2 is improved, but the thermostability decreases due to the introducing of active C-I bond. Functional polymers FCP2 were prepared by grafting p-carbomethoxy phenylacetylene in side-chain using the reactivity of C-I bond, which possess high thermostability, and exhibit red-shifted absorption and emission spectra due to their enlarged conjugated structures.