Assembly of Functional Nanostructures for Optical, Electrical or Catalytic Systems

Abstract

The aim of this PhD thesis is the fabrication and study of nanostructures showing optical, electrical or catalytic properties in the perspective of applications in different fields of the nanotechnology. An important aspect is represented by the method we used to manufacture these nanostructures. In fact, all synthesized systems are based on the covalent assembly of discrete molecules (organic molecules or inorganic complexes) on inorganic surfaces. The present molecules (building blocks) show interesting properties e.g. optical or catalytic activity, while the substrate materials are appropriate for applications of the final structures in the optoelectronic, microelectronic or catalytic industries. Often, by changing just the inorganic substrate the same covalently assembled building blocks exhibit different properties and this is an evidence of the fact that single-molecules properties can be affected by the substrate nature upon anchoring. For example, anchoring of optically active molecules such as porphyrins to Si(100) substrates allows to exploit optoelectronic properties while the same porphyrin molecules on SnO2 and TiO2 nanocrystals provide electron injection on the semiconducting surfaces useful for photovoltaics. Moreover, we also investigated optical active surfaces upon the self-assembly of porphyrin molecules functionalised with luminescent Eu(III) complexes in order to exploit the mutual interaction of systems whose luminescence is based on different mechanisms. In the same context, we functionalised a covalent polystirene film on a quartz substrates with an Eu(III) complex to examine the possibility to obtain tunable light emitting properties useful to transfer optical information. The covalent assembly of porphyrins and Eu(III) complexes can be applied also to electroactive substrates as CdO, ITO, ZnO, etc. in the perspective of microelectronic applications. For this reason we optimized the deposition of high conducting CdO thin films by a metallorganic chemical vapour deposition route. Finally, we studied the activity of some (salen)Mn(III) molecules covalently assembled on glass beads in the epoxidation of unfunctionalised prochiral olefins with the aim of increasing the catalytic behaviour upon heterogeneization thus obtaining huge turnover numbers. In summary the most important achievement of this thesis is to have demonstrated that the covalent assembly of suitable molecules on appropriate inorganic surfaces allows the synthesis of molecular architectures showing unique properties appealing for future technologies.