Functional isocoumarin-containing polymers synthesized by rhodium-catalyzed oxidative polycoupling of aryl diacid and internal diyne

An atom-economical and straightforward polymerization method to generate functional isocoumarin-containing polymers was developed in this work. The oxidative polycoupling of 4,4′-(1,2-diphenyl-1,2-ethenylene)dibenzoic acid and 1,6-bis[4-(phenylethynyl)phenoxy]hexane proceeds efficiently in dimethylformamide under nitrogen or air in the presence of [Cp∗RhCl₂]₂ and a catalytic amount of Cu(OAc)₂·H₂O at 120 °C for 24 h, generating a polymer with a high molecular weight of up to 42 900 in a high yield of up to 92.9%. An isocoumarin framework forms in situ during the polymerization from readily accessible and inexpensive monomers. The resulting polymer possesses good thermal stability, optical transparency and film-forming ability. Its thin film exhibits high and UV-tunable refractive indices (n = 1.9697-1.6507) in a wide wavelength region of 390-890 nm. A two-dimensional fluorescent photopattern can be readily fabricated by irradiating its thin film under UV light through a copper mask. Due to the incorporation of tetraphenylethene units in the monomer, the polymer obtained is weakly emissive in solution but it emits intensely when aggregated, demonstrating a phenomenon of aggregation-induced emission.