The synthesis and electro-optic properties of polyimide/silica hybrids containing the benzothiazole chromophore

A series of polyimide/silica NLO hybrid materials were synthesized from pyromellitic dianhydride, 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane, nonlinear optical molecule 4-(N-2-hydroxyethyl-N-methylamino)-4′-[(6-nitrobenzothiazol-2-yl)diazenyl]azobenzene via a sol–gel process; the tetraethoxysilane content in the hybrid films was varied from 0 to 22.5%. The prepared polyimide/silica hybrids were characterized by FT-IR, differential scanning calorimeter, thermogravimetric analysis, scanning electron microscopy, transmission electron microscope and X-ray diffraction. The glass transition temperature and decomposition temperature at 5% mass loss were in the range 214–360 °C and 317–428 °C, respectively, showing that the hybrid materials had excellent thermal stability. Polymer solutions were spin-coated on indium–tin-oxide glass, forming optical quality thin films. The electro-optic coefficients at 832 nm for poled polymer thin films were ≈20 to 33 pm/V and the values were retained >88% for more than 100 h. The experimental results suggest that the hybrid thin films have potential applications as passive films for optical devices.