Azo chromophore monomerically bonded mesostructured silica films with large third-order nonlinearity but negligible nonlinear absorption

The azobenzene chromophore covalently and monomerically dispersed mesostructured organic-inorganic hybrid films were prepared by a direct-synthesis route thanks to the compatible environment provided by the hydrophobic core of the surfactant micelles. The third-order optical nonlinearity of this mesostructured organic-inorganic hybrid was investigated by using the Z-scan technique in/near the two-photon absorption region (at 1064 nm). It is very interesting that no two-photon absorption could be detected in/near the twophoton absorption region, which is in contrast to those in solution and common nonmesostructured films. Meanwhile, a large nonlinearity with a nonlinear refractive index n₂ of 10^-9 esu, purely attributed to electronic effect, has been obtained. The special structure, that the hydrophilic alkoxysilane end is covalently anchored on the silica pore surface while the opposite hydrophobic chromophore end is monomerically dispersed in mesopore space, is believed to be responsible for the uncommon nonlinear optical properties. As a result, the special nonlinear optical properties of such mesostructured films can well satisfy the Stegmen figures of merit for the demands of all-optical devices applications.