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 (T_g > 180°C). Their poled films exhibit nigh second-harmonicgeneration 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).