Nanostructuring of organic materials templated by hydrogen bonding recognition

The central challenge in the construction of molecular based devices is the necessity to develop methods for the controlled fabrication of well-defined organic systems that meet the structural requirements for their nanotechnological applications. The aim of this thesis is to design and synthesise novel molecules, equipped with desired molecular functionalities, which by means of H-bonding interactions can self-assemble and generate complex nanostructures both in solution and on metallic surfaces that ultimately could find applications as optoelectronic devices. Intrinsically, our goal is to obtain a good understanding of the recognition and complexation behaviour of the functional molecules either in solution or on surfaces. Our approach is based on the preparation of a vast †œmolecular library†� of smart molecules, which can self-recognise and organise in a predictable manner. The synthesis of geometrical molecular modules bearing complementary H-bonding sites (2,6-di(acetylamino)pyridine and uracil) for self-assembly studies on metallic surfaces has been described. Such molecules however, showed some solubility limitations in common organic solvents such as CHCl3 or CH2Cl2, which represents a considerable disadvantadge for performing studies in solution. In fact, some of the molecules used in our studies could only be characterised in very polar solvents such as dimethylsulfoxide (DMSO), which are strong hydrogen bonding acceptor solvents, and therefore unsuitable for recognition studies. To solve this problem we synthesised a new generation of modules based on the former ones, which presented an enhanced solubility in common organic solvents and thus more appropriate for recognition studies in solution. The supramolecular complexes were characterised by means of 1H-NMR titrations and Job plots as well as steady-state UV/VIS absorption and emission titration measurements to determine the association strength and the assemblies' stoichiometry. As expected, the recognition between the uracil and the 2,6-di(acetylamino)pyridine moieties is the driving force for the formation of the supramolecular systems. Self-organisation studies in solution of some supramolecular systems were also performed and the formation of spherical nanostructures resembling vesicles was observed. Finally, the †œbottom-up†� fabrication of patterned surfaces based on the supramolecular recognition of the pre-programmed complementary modules was performed. The Scanning Tunneling Microscopy studies performed both on the solid-liquid and solid-vacuum interfaces unravelled the potential of the supramolecular approach in the fabrication of addressable molecular devices, which are hardly imaginable using established miniaturising methods such as the lithographic techniques.