Abstract:
Organic second-order nonlinear optical (NLO) materials have broad application prospects in a new generation of high-performance, high-bandwidth electro-optic modulation devices due to their high responsiveness, high integration, low cost, and good designability. However, the organic second-order NLO materials present relatively lower alignment stability compared with inorganic materials, which limits its wide application. In this paper, cross-linkable anthracene groups are introduced into the side chains of polymer for enhancing alignment stability by 4+4 cycloaddition reaction of anthracene groups under UV light irradiation. Methylmethacrylate based copolymers p1 —p3 containing different concentration of anthracene groups were synthesized by solution polymerization. Then chromophores were doped in p1—p3 to prepare second-order nonlinear optical films. The time required for the complete reaction of anthracene groups in the polymer film was studied by UV-Vis spectroscopy. After 30 min irradiation, the crosslinking reaction could complete and the chromophores during irradiation didn’t exhibit decomposition. The results of differential scanning calorimetry (DSC) showed that the glass transition temperature(
Tg) of the polymer film increased by 10 ℃ after the cross-linking reaction. As the TGA analysis, 5% mass fraction decomposition temperature increased with anthracene group from 210 ℃ to 240 ℃. The electro-optic properties and orientation stability of the cross-linked materials were investigated. After heating at 60 ℃ for 220 h, electro-optic properties retained around 90% after photo-crosslinking. Peak temperature of the thermal stimulated current (TSD) of the crosslinked film increased around 15 ℃ compared with uncrosslinked one. The results show that the orientation stability of the second-order nonlinear polymer has been improved to a certain extent.