Bridged polysilsesquioxanes with improved second order nonlinear optical properties and stability

We report the synthesis and sol-gel polymerization of 4-nitro-N,N-bis[(3-triethoxysilyl)propyl]aniline 1. An efficient synthesis of the monomer was developed by the hydrosilylation of N, N-diallyl-4-nitroaniline. Optical quality thin films were synthesized by spin coating an n-butanol solution of 1 using formic acid as catalyst and source of water. We improved the temporal stability of the NLO signal from films prepared from 4-nitro-N,N-bis[(3-triethoxysilyl)propyl]aniline by increasing the intensity of the poling field and extending the heating period during the poling/curing stage. By Maker fringe analysis, a χ⁽²⁾ value of 9 × 10^-8 esu was measured for these polysilsesquioxanes. If one assumes that the major component of the NLO effect is along the z-axis, the χ⁽²⁾ value corresponds to a d₃₃ coefficient of 18.p pm/V and a r₃₃ value of 4.7 pm/V.