Zwitterionic polymers for nonlinear optics

Good optical quality thin films could be obtained with zwitterionic polymaleimides grafted by pyridinium-phenoxide zwitterions and also with polymethylmethacrylate (PMMA) doped by the same chromophores. Zwitterionic grafted polymaleimides presented low nonlinear efficiencies. Conversely, orientation of the PMMA doped films by the corona method could easily be performed and led to efficient systems for second-harmonic generation. Orientation within the doped films and susceptibility coefficients were very stable with time. Since doped polymers readily loose their orientation generally, the stability of these zwitterionic systems must be highlighted. The efficiency of zwitterionic doped PMMA films was of the same order as that of classical guest-host systems of PMMA such as DR 1, DO3, DCV and TCV. Illumination of zwitterionic grafted or doped polymers in the chromophore absorption band and during the corona poling led to a reversible depoling of thin films. The poling was restored when the illumination was switched off. A cycling of poling-depoling, monitored by the external light illumination, led to an enhanced polar orientation as well as to an enhanced temporal stability of the induced order, as checked by the in situ second-harmonic generation experiments. This perfectly reversible effect, accompanied by the light-induced refractive index variation of thin film, should find numerous practical applications. (C) 2000 Elsevier. Science B.V. All rights reserved.