Active organic molecules are grafted on the xerogel silica matrix by using functionalized alkoxides f-R′–Si(OEt)3, where f is a chemical function and R′ is an alkyl spacer to limit the degrees of freedom of the molecules. Organic-inorganic hybrid films are prepared in which optically nonlinear DRl chromophores are covalently bound to the silica network. These films exhibit a large and stable second-order nonlinear coefficient from second harmonic generation experiments. Protoporphyrin molecules are attached double covalently to the xerogel matrix via flexible organic spacers. Persistent spectral holes are still burnt with moderate fluency at 120 K.