Photo-crosslinkable second order nonlinear AB2-type monomers: convenient synthesis and enhanced NLO thermostability

Abstract

In this article, two AB₂-type second-order nonlinear optical monomers (DN-SH and DS-SH) containing two double bonds and one thiol group, respectively, were synthesized successfully. These two monomers could be in situ photo-crosslinked via a thiol–ene click reaction under 365 nm UV light without a photoinitiator after poling. Thanks to the photo-crosslinking process of thin films, the thermostability of the second-order nonlinear optical property was much enhanced. DS-SH exhibited a larger NLO effect and better NLO thermostability than DN-SH, because of the introduction of sulfonyl-based chromophores which can decrease the electrostatic interaction between nitro-based chromophore moieties. T_80% of the photo-crosslinked DS-SH films increased to 112.5 °C, much higher than that of uncrosslinked ones (75 °C), while T_80% of DN-SH films increased from 58 to 95 °C. More excitedly, the doped thin films of DN-SH and DS-SH at different molar ratios (1 : 1, 2 : 1, and 1 : 2) showed better NLO properties (123, 122, and 114 pm V⁻¹, respectively) after photo-crosslinking than single DN-SH (89 pm V⁻¹) and DS-SH (108 pm V⁻¹) respectively.