Alternate synthetic approaches for soluble second-order nonlinear optical polyimides

Several soluble second-order nonlinear optical (NLO) polyimides with various chromophore structures were synthesized by two alternate synthetic approaches to overcome the disadvantages of currently used methods. In the first approach, the NLO polyimides were prepared by the step-growth polymerization reaction between a chromophore-containing dianhydride and diamine compounds. This method can avoid the troublesome syntheses of the chromophore-containing diamine and can provide easy preparation of the polyimides with various chromophores. In the second approach, we synthesized the NLO polyimides by the simple one-step Mitsunobu reaction between NLO-diol compounds and diimides. Using this method, the polyimide system was directly formed during condensation polymerization without thermal imidization step at high temperatures. All polymers derived from these new synthetic routes exhibited high second harmonic generation (SHG) activities as well as good thermal and temporal stabilities of the SHG signal.