Sol-gel hybrid Organic/inorganic Nanocomposites by condensation reactions of diphenylsilanediol and organo-alkoxysilanes for photonic applications.

Sol-gel derived hybrid organic/inorganic (O/I) nanocomposites are largely exploited in materials technology, due to the synergic merge at the molecular scale of the components characteristics through a large extent of phase interaction. Thanks to their structural flexibility, hybrid materials are being increasingly used for a variety of applications in the field of integrated optics for the development of both passive and active devices. Since the control of molecular and supramolecular structures is a fundamental issue for properties tailoring, recent research has focused on the synthesis of nanocomposites by assembling nanobuilding blocks (nbb), a technique that allows attaining nanometric control of the final materials. Si-based nanobuilding blocks are nanosized-preformed objects that can build up an organic/inorganic network exploiting the reactivity of organosilanes with functional end-capping organic groups. We here report a review of our main results on the preparation and characterization of sol-gel hybrid organic/inorganic (O/I) nanocomposites by the assembling of silicon–based nbb, prepared by condensation of diphenylsilanediol with organo-alkoxysilanes and metal alkoxides. Two different methodologies have been followed: the condensation reaction was run both in non-hydrolytic conditions and using a controlled hydrolytic process, by means of in situ water production. Several techniques, such as multinuclear NMR, FTIR, FT-Raman and GPC, have been used to clarify the reaction pathways, with analysis of intermediate species, and to characterize the molecular complexity as well as the ratios between linear and cyclic Si oligomers in the final nbb. High refractive index hybrid coatings were prepared by nbb assembling in different matrices. The thermal polymerization process and the two-photon induced polymerization (TPIP) process for the preparation of patternable films from methacrylate-based nbb were studied using DSC and FE-SEM analyses. Highly cross-linked networks have been obtained leading to patternable films with well-defined and small structures.