Linear and nonlinear optical properties of linear and hyperbranched conjugated polymers

Azo-functionalized hyperbranched polymers 1 and 2, and linear polyacetylene 3 are synthesized by palladium-catalyzed coupling of triiodoarenes with a diethynylazobenzene, and post functionalization, respectively. These polymers are soluble, film-forming, and morphologically stable (T _g > 180°C). The poled polymer films of 1 and 2 exhibit high second-harmonic generation coefficients (d ₃₃ up to 177 pm/V), thanks to the chromophore-separation and site-isolation effects of hyperbranched architectural structure of the polymers in the three-dimensional space. The poled film of polymer 3 shows the trade-off of nonlinearity-transparency-orientation thermal stability. The poled films are all orientationally and thermally stable due to the facile cross-linking of the multiple acetylenic triple bonds in the hyperbranched polymer and the rigid backbone in the linear polyacetylene, respectively.