Polyamides alternately substituted with an aliphatic cyclic moiety and an NLO-phore for second-order nonlinear optics

摘要

This article describes the synthesis and second-order nonlinear optical (NLO) properties of polyamides containing an alternating arrangement of cholesteryl or menthyl moieties and an NLO-phore, i.e., N,N-dialkyl-4-nitroaniline, in the side chain. The poly amides were prepared by condensation polymerization of 5-2-(N-methyl-4-nitroanilino)ethoxyisophthaloyl chloride with cholesteryl (P1) or L-menthyl (P2) 3,5-diaminobenzoate. The resulting polyamides PI and P2 exhibit high glass transition temperatures (T-g) around 200 degrees C and good solubilities in common organic polar solvents. Optical-quality films of P1 and P2 were obtained by spin-coating. The second harmonic generation (SHG) measurements of the spin-coated films of P1 and P2 were carried out by the Maker fringe method using a Q-switched Nd:YAG laser (1064 nm) as exciting beam after corona-poling; they indicate that P1 and P2 exhibit a second-order NLO coefficient, d(33), of 10 pm/V. The orientational behavior of the NLO-phores in P1 is specific for the poling process. A noncentrosymmetric alignment of the NLO-phores in P1 was induced by corona-poling at a temperature lower than T-g, i.e. at 100 degrees C. Additionally, it was found that the noncentrosymmetric alignment of NLO-phores in P1 is inhibited over 160 degrees C due to the para-crystalline aggregation of cholesteryl moieties as deduced from the SHG measurements and X-ray diffraction analysis. References: 19