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The formation of highly ordered self-assembled monolayers (SAMs) is of remarkable interest in the development of functional patterned surfaces for electronic applications as Quantum-dot Cellular Automata (QCA). QCA exploit quantum confinement, tunnelling and electrostatic interaction for transistor-less digital computing. In QCA, quantum dots are arranged in functional units called cells connected by tunneling pathways and containing, each, two mobile charges. Cells are capable to represent Boolean states (1 and 0) and to transfer the information to the neighbouring cells by electronic interaction. The logical function computed is then related to the topology of the cell network. To create an electronic device based on QCA concept, is therefore of fundamental importance that the cells organize themselves in a high ordered manner on the surface. Self-assembly of metal-complexes at liquid-solid interface was recently studied by different research groups, and it could be exploited for fix QCA cells on surfaces. Here we report our recent results on the supramolecular behaviour of aluminium salophen complexes. The molecules prepared presented a strong ordered self-assembly at the solid-liquid interface as evidenced by scanning tunnelling microscopy (STM), where the structure exhibits parallel and linear arrays. The possibility to prepare a penta-coordinate aluminium complex by treatment of MeAl(Salophen) complexes by direct reaction with acidic phenols open the way to the installation of different functionalities on the aluminium complexes. As these are strongly organize on the surface, a high ordered functionalization of the surface can be obtained.

The main aims of my PhD research work have been the investigation of the redox, photophysical and electronic properties of carbon nanotubes (CNT) and their possible uses as functional substrates for the (electro)catalytic production of oxygen and as molecular connectors for Quantum-dot Molecular Automata. While for CNT many and diverse applications in electronics, in sensors and biosensors field, as a structural reinforcing in composite materials have long been proposed, the study of their properties as individual species has been for long a challenging task. CNT are in fact virtually insoluble in any solvent and, for years, most of the studies has been carried out on bulk samples (bundles). In Chapter 2 an appropriate description of carbon nanotubes is reported, about their production methods and the functionalization strategies for their solubilization. In Chapter 3 an extensive voltammetric and vis-NIR spectroelectrochemical investigation of true solutions of unfunctionalized individual single wall CNT (SWNT) is reported that permitted to determine for the first time the standard electrochemical potentials of reduction and oxidation as a function of the tube diameter of a large number of semiconducting SWNTs. We also established the Fermi energy and the exciton binding energy for individual tubes in solution and, from the linear correlation found between the potentials and the optical transition energies, one to calculate the redox potentials of SWNTs that are insufficiently abundant or absent in the samples. In Chapter 4 we report on very efficient and stable nano-structured, oxygen-evolving anodes (OEA) that were obtained by the assembly of an oxygen evolving polyoxometalate cluster, (a totally inorganic ruthenium catalyst) with a conducting bed of multiwalled carbon nanotubes (MWCNT). Here, MWCNT were effectively used as carrier of the polyoxometallate for the electrocatalytic production of oxygen and turned out to greatly increase both the efficiency and stability of the device avoiding the release of the catalysts. Our bioinspired electrode addresses the major challenge of artificial photosynthesis, i.e. efficient water oxidation, taking us closer to when we might power the planet with carbon-free fuels. In Chapter 5 a study on surface-active chiral bis-ferrocenes conveniently designed in order to act as prototypical units for molecular computing devices is reported. Preliminary electrochemical studies in liquid environment demonstrated the capability of such molecules to enter three indistinguishable oxidation states. Side chains introduction allowed to organize them in the form of self-assembled monolayers (SAM) onto a surface and to study the molecular and redox properties on solid substrates. Electrochemical studies on SAMs of these molecules confirmed their attitude to undergo fast (Nernstian) electron transfer processes generating, in the positive potential region, either the full oxidized Fc+-Fc+ or the partly oxidized Fc+-Fc species. Finally, in Chapter 6 we report on a preliminary electrochemical study of graphene solutions prepared according to an original procedure recently described in the literature. Graphene is the newly-born of carbon nanomaterials and is certainly bound to be among the most promising materials for the next nanoelectronic generation.

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Salophens and Salens are Schiff bases generated through the condensation of two equivalents of salicylaldehyde with either 1,2-phenylenediamines or aliphatic diamines, respectively. Both ligands have been extensively exploited as key building blocks in coordination chemistry and catalysis. In particular, their metal complexes have been widely used for various catalytical transformations with high yield and selectivity. Through the modification of the phenol unit it is possible to tune the steric hindrance and electronic properties of Salophen and Salen. The introduction of long aliphatic chains in salicylaldehydes can be used to promote their self-assembly into ordered supramolecular structures on solid surfaces. Herein, we report a novel method towards the facile synthesis of robust and air-stable [Al(Salophen)] derivatives capable of undergoing spontaneous self-assembly at the graphite/solution interface forming highly-ordered nanopatterns. The new synthetic approach relies on the use of [MeAlIII (Salophen)] as a building unit to introduce, via a simple acid/base reaction with functionalized acidic phenol derivatives, selected frameworks integrating multiple functions for efficient surface decoration. STM imaging at the solid/liquid interface made it possible to monitor the formation of ordered supramolecular structures. In addition, the redox properties of the Salophen derivatives functionalized with ferrocene units in solution and on surface were unraveled by cyclic voltammetry. The use of a five-coordinate aluminum alkyl Salophen precursor enables the tailoring of new Salophen molecules capable of undergoing controlled self-assembly on HOPG, and thereby it can be exploited to introduce multiple functionalities with subnanometer precision at surfaces, ultimately forming ordered functional patterns.

The electrochemistry of a family of recently synthesized isoalloxazine cyclophanes containing anthraquinones, variously substituted and linked by aliphatic chains of different lengths, has been studied. The redox behavior of such species was elucidated by complementing the voltammetric studies with DFT molecular modelling. In these cyclophanes (mimicking the active centers of enzymes), the distance between chromophores and their reciprocal orientations were found to significantly modify their redox properties. Inter-moiety π−π stacking plays an important role in the electrochemical behavior by modulating the orbital energies, which leads to an inversion of the localization of the first reduction, with the anthraquinone being reduced before the more electron-accepting flavine.

Indium tin oxide (ITO) and silicon with a thermally grown SiO2 layer (Si/SiO2) substrates have been functionalized by ferrocene bound through Sn(O)x (x=2 or 3) linkers preliminarly grafted on the surface by reaction of the terminal hydroxyl groups with tetra(tert-butoxy)tin. The two steps modification of the surface was carried out by chemical vapour deposition metathesis reaction producing a self-assembled monolayer of ferrocene. The ITO and Si/SiO2 thus functionalized have been characterized by voltammetric, amperometric, electrochemical impedance spectroscopy and scanning probe microscopy techniques which assessed the formation of a stable and rather compact covalently bound ferrocenyl monolayer with improved electron transfer properties.

The synthesis of two A2B2 porphyrins, {5,15-bis-[4-(octyloxy)phenyl]-porphyrinato}zinc(II) (4) and {5,15-bis- (carbazol-3-yl-ethynyl)-10,20-bis-[4-(octyloxy)phenyl]-porphinato}-zinc(II) (9), is reported. Their photophysical properties were studied by steady-state absorption and emission. Substituting the carbazolylethynyl moieties at two of the meso positions results in a large bathochromic shift of all the absorption bands, a notable increase in the absorption coefficient of the Q(0,0) band, and higher fluorescence quantum yield compared to porphyrin 4, with two unsubstituted meso positions. Cyclic voltammetry and digital simulation show that electrogenerated radical ions of 9 are more stable than those of 4. The lack of substituents at the meso positions of 4 leads to dimerization reactions of the radical cation. Despite this, the annihilation reaction of 4 and 9 produces very similar electrogenerated chemiluminescence (ECL) intensity. Spectroelectrochemical experiments demonstrate that the electroreduction of 9 leads to a strong absorption band that might quench the ECL.