Facile Synthesis, Large Optical Nonlinearity, and Excellent Thermal Stability of Hyperbranched Poly(aryleneethynylene)s Containing Azobenzene Chromophores

Azo-functionalized hyperbranched poly(aryleneethynylene)s (hb-PAEs) (4 and 5) are synthesized by palladium-catalyzed coupling of triiodoarenes (1 and 2) with a diethynylazobenzene (3). The hb-PAEs are soluble, film-forming, and morphologically stable (Tg > 180 °C). Their poled films exhibit high second-harmonic-generation coefficients (d33 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 optical nonlinearities of the poled films are thermally stable (no drop in d33 when heated to 152 °C) due to the facile cross-linking of the multiple acetylenic triple bonds in the hb-PAEs at moderate temperatures (down to 88 °C).