Monomer stoichiometry imbalance-promoted formation of multisubstituted polynaphthalenes by palladium-catalyzed polycouplings of aryl iodides and internal diynes

Abstract

A new monomer stoichiometry imbalance-promoted polymerization tool for the synthesis of functional polymers was designed and investigated in this work. The polymerizations of aryl iodides and internal diynes were catalyzed by widely available Pd(OAc)₂ and additives in o-xylene at 80 °C, producing a series of multisubstituted polynaphthalenes (PNs) with high molecular weights (up to 48 100) in nearly quantitative yields. The presence of excess aryl iodides significantly improved the reaction efficiency of these polymerizations and the underlying working mechanism was detailedly investigated. All the obtained polymers exhibited excellent solubility in common organic solvents and good film-forming ability. Their thin films possessed high refractive indices (n = 1.9013–1.6340) in a wide wavelength range of 380–890 nm. Fluorescent conjugated PNs were formed when tetraphenylethylene (TPE)-containing diynes were used. Taking advantage of their efficient solid-state emission and photosensitivity, well-resolved photopatterns with green emission can be generated by irradiating their thin films under UV light through copper masks. Moreover, all the polymers showed great thermal stability, losing merely 5% of their weight at a high temperature of 387–458 °C under nitrogen and at 350–392 °C in air. The TPE-containing PNs retained 72–79% of their weights after being heated to 800 °C under nitrogen due to their conjugated polymer backbones.