Synthesis and characterization of accordion main-chain azo-dye polymers for second-order optical non-linearity

New type accordion polymers with azo-dye chromophores as the major segments (up to 70% by weight) of the main chain for second optical non-linearity (NLO) are designed and synthesized by the Knoevenagel polycondensation between bis(carboxaldehyde) containing azobenzene and bis(cyanoacetate) comonomers. Several important properties for NLO application, such as solubility and thermal stability, are investigated, and the effects of linkage groups on the physical properties of polymers are also discussed in some detail. Poled films of one of these polymers show a relatively high resonant d₃₃ value of 33pmV^-1 by second harmonic generation (SHG) measurement, and their order parameter, which is determined to be 0.20 by UV-vis measurement, keep almost constant for 240 h at ambient temperature.