Effect of chromophore-chromophore electrostatic interactions in the NLO response of functionalized organic-in organic sol-gel materials

In the last years, important non-linear optical (NLO) results on sol-gel an d polymeric materials have been reported, with values comparable to those f ound in crystals. These new materials contain push-pull chromophores either incorporated as guest in a high T-g polymeric matrix (doped polymers) or g rafted onto the polymeric matrix. These systems present several advantages, however they require significant improvement at the molecular level-by des igning optimized chromophores with very large molecular figure of merit, sp ecific to each application targeted. Besides, it was recently stated in pol ymers that the chromophore-chromophore electrostatic interactions, which ar e dependent of chromophore concentration, have a strong effect into their N LO properties. This has not been explored at all in sol-gel systems. In thi s work, the sol-gel route was used to prepare hybrid organic-inorganic thin films with different NLO chromophores grafted into the skeleton matrix. Co mbining a molecular engineering strategy for getting a larger molecular fig ure of merit and by controlling the intermolecular dipole-dipole interactio ns through both: the tuning of the push-pull chromophore concentration and the control of tetraethoxysilane concentration, we have obtained a coeffici ent around 15 pm/V at 633 nm for the classical DR1 azo-chromophore and a r( 33) around 50 pm/V at 831 nm for a new optimized chromophore structure. (C) 2001 Elsevier Science B.V. All rights reserved.