In this paper, second-order NLO chromophores containing two reactive sites have been synthesized and characterized by H-1 NMR, FTIR and elemental analysis. The transparent films have silica network of matrix and covalently bonded chromophore of NLO segment were then fabricated via sol-gel process. The SHG coefficients (d(33)) of the poled films were calculated to be around 50 pm/V by in situ second harmonic generation (SHG) measurement. The thermal stability of the NLO coefficient was investigated by the depoling experiment and temporal decay test, showing that the cross-linked films had a good thermal stability up to 160 degrees C. (c) 2007 Elsevier B.V. All rights reserved.