Poling and its relaxation studies of polycarbonate and poly(styrene-co-acrylonitrile) doped by a nonlinear optical chromophore

Spin-coated films of poly(bisphenol A carbonate) (PC) and poly(styrene-co-acrylonitrile) (SAN) doped by 4-(N,N-dimethylamino)-4′-nitrostilbene (DANS) were prepared, and their poling and depoling behaviors were investigated mainly by UV–visible absorption spectra and second-harmonic generation (SHG). The absorbance of DANS in the PC and SAN films proportionally increased with increasing its weight concentration up to 5 wt%, indicating homogeneous dissolution of DANS in the host polymers. However, above this concentration, heterogeneous structures due to DANS crystallites could be observed under a polarizing microscope. Poling of the films was performed using a triode corona discharging system. The maximum d coefficients were obtained at slightly lower poling temperature than the glass transition temperature of the corresponding dye-doped polymer. The KWW stretched exponential function could be fitted to the experimental temporal relaxation data of SHG for the SAN system. Relatively high long-term stability was observed for the PC system because of its relatively rigid backbone structure.