Polyamides for Nonlinear Optics: Side-Chain All Donor-Attached NLO-phores versus Side-Chain Alternating Donor-Attached and Acceptor-Attached NLO-phores

This article describes the syntheses and second-order nonlinear optical (NLO) properties of a novel type of polyamide with side-chain alternating donor-attached and acceptor attached NLO-phores as well as polyamide with side-chain all donor-attached NLO-phores. Two kinds of polyamides were prepared by condensation polymerization between 5-[2-( N -methyl-4-nitroanilino)ethoxy]isophthaloyl chloride and 3-{[4-(dihexylamino)phenyl]sulfonyl}propyl 3,5-diaminobenzoate ( P3 ) or 2-[ N -methyl-4-(octylsulfonyl)anilino]ethyl 3,5-diaminobenzoate ( P4 ). In the side chain of P3, electron-donating and electron-withdrawing groups of the NLO-phores were alternatingly attached. The obtained polyamides exhibited good solubility in common organic solvents and provided optical-quality films by spin-coating. The second-harmonic generation (SHG) measurements of the obtained polyamides were carried out by the Maker fringe method using a Q-switched Nd:YAG laser as an exciting beam after corona-poling at various temperatures, indicating that P3 and P4 exhibited the optimum second-order NLO coefficient, d 33, of 6.4 and 7.1 pm/V, respectively. There were no significant differences in the temperature dependence of orientational behavior between two kinds of polyamides. The preliminary measurements of the short-term temporal SHG decay suggested that it is possible for the relaxation of the NLO-phore orientation in P3 to be somewhat restricted, as far as deduced from the values of time coefficient obtained by curve-fitting to the SHG decay curves.