Spectroscopic investigation on noble metal-organic nanohybrids with controlledshapes and properties

Hybrid compounds obtained by a bottom-up technique consisting of self-assemblingproperly functionalized organic molecules onto preformed nanosized cores of noble metalsrepresent very promising materials for applications in both industrial and medical fields. Theiroptical, spectroscopic and functional properties can be easily modulated by mastering size andshape of the metal core as well as the chemical nature of the organic shell.To this end we prepared gold and silver nanoclusters with different geometries(spheres, rods, cages, ribbon-like assemblies, stars) by reduction of the corresponding salt inaqueous solution, properly manipulating the synthesis protocol. The morphology of the as-preparedcolloids was characterized by TEM technique and confirmed by spectroscopicanalysis. The plasmonic absorption are tuned throughout the visible and near-infrared (NIR)region in relation to nanostructure size, shape, aggregation state and local environment. Theso prepared nanostructures were then passivated with properly functionalized molecules likechromophores and diacetylenic monomers by taking advantage of the well-establishedmonolayer chemistry. The optical properties of the novel nanohybrids were investigated byUV-Vis and Raman techniques in order to evaluate the role of the metal nanostructures on thebehaviour of the chemisorbed molecules and on their sensitivity to the environmental changes[1]. Photopolymerized diacetylene monomers bonded to these nanostructures [2,3]represent promising materials with strong electromagnetic field enhancements in the NIRregion without need of properly structured metallic nanoparticolates to induce hot-spots [4].This opens the way to the implementation of nonlinear optical effects and to devices, likeswitches or modulators, for telecom applications. Moreover, the use of these nanostructuresallows the extension of well established spectroscopic diagnostics, like SERS, in this spectral region.