Palladium-catalyzed polyannulation of pyrazoles and diynes toward multifunctional poly(indazole)s under monomer non-stoichiometric conditions

A new synthetic route toward multifunctional poly(indazole)s (PIs) with an effect of monomer stoichiometry imbalance-promoted polymerization is described in this work. The palladium-catalyzed oxidative polyannulations of internal diynes and 1-methylpyrazole proceed smoothly in 1,4-dioxane at 120 °C with copper acetate monohydrate functioning as the oxidant. A series of PIs with high molecular weights (M_w up to 35 800) are generated in good yields (up to 84.0%) under monomer non-stoichiometric conditions. These polymers exhibit high thermal stability, losing merely 5% of their weights at high temperatures of 321-353 °C. The solid thin films of these PIs show high and UV-tunable refractive indices (n = 1.8870-1.6051) in a wide wavelength range of 400-900 nm. The tetraphenylethene-containing PI shows obvious solid-state emission properties and good photosensitivity. Its thin film was successfully fabricated into a well-defined two-dimensional fluorescent photopattern with sharp edges.