Enhanced thermal stability of dipole alignment in inorganic-organic hybrid films containing benzothiazole chromophore

A new thermally stable second-order nonlinear optical (NLO) inorganic-organic hybrid film was successfully prepared by using a sol-gel process of alkoxysilane dye containing a benzothiazole unit. The dye-bonded precursor was synthesized from 3-isocyanatopropyltriethoxysilane and the heterocycle azo dye 2-[4'-(N-ethyl-N-2-hydroxyethyl)-amino-phenylazo]-6-nitrobenzothiazole (EHNBT) via a urethane reaction. Molecular structural characterization for the resultant was achieved by elemental analysis, FTIR, UV-visible spectra, and H-1 NMR. The second harmonic coefficients (d(33)) of poled hybrid films measured by a Maker fringe technique were in the range 15.9-72.1 pm/V at a wavelength of 1064 nm, depending on the concentration of alkoxysilane dye. The hybrid films containing the benzothiazole moiety exhibited higher thermal stability of dipole alignment at elevated temperatures than their analogues with a benzene ring. The d33 value of the poled film remained at 94% of its initial value after heating at 120 degrees C for 6 h, and only 18% decayed in 15 min at 180 degrees C. The result indicates that the hybrid film is suitable for the fabrication of an electro-optic device.