Synthesis and characterization of nonlinear optical side-chain polyimides containing the benzothiazole chromophores

A series of polyimide-based second-order nonlinear optical (NLO) materials were synthesized from poly(hydroxy-imide)s, followed by the Mitsunobu reaction with NLO chromophores. These chromophores, based on a nitro group connected with benzothiazole as the acceptor end of a donor-pi -bridge-acceptor chromophore and a hydroxy-functional amino group as the donor end, have specific chemical stability. The resulting polymers were highly soluble in aprotic polar solvents such as DMF, DMAc, NMP, etc. Molecular structural characterization fur these polymers was achieved by H-1 NMR, FT-IR, and W-visible spectroscopes. The glass transition temperature for the resulting NLO polyimides was in the range 197-247 degreesC, and most of them showed high thermal stability. The polymer solutions could be spin coated on the indium-tin-oxide (ITO) glass or other substrates to form optical quality thin films. The electrooptic coefficients (gamma (33)) at the wavelength of 830 nm for polymer thin films poled around the optimal temperature (T-opt) were in the range of 9-32 pm/V, and the value remained well at elevated temperatures for move than 120 h in the air. The NLO stability of these polyimides was also studied by studying the UV-visible spectra of their poled films.