Molecular self-assembly for synthesis of nanostructures

Molecular self-assembly is a convenient, flexible, and powerful strategy that allows one to transform molecular building blocks into well-defined nanostructures in a controllable manner. This thesis explores the combination of natural and synthetic molecules and self-assembly strategy to create sophisticated and functional nanostructures. In some cases, nanofabrication techniques are used to assist the synthesis and organization of nanostructures.;CHAPTER TWO demonstrates Dip-Pen Nanolithography as a suitable approach for the synthesis of phospholipid nanostructures with ultrahigh lateral resolution (below 100 nm) and areal throughput (5 cm2/min) on a variety of substrates. This approach allows one to rapidly pattern multi-component lipids in parallel. The resulting nanostructures are stable under ambient conditions and retain the biological functions, like fluidity, of lipids. Furthermore, the three-dimensional sheet-like multi-lamellar architectures of lipid nanostructures are revealed.;In CHAPTER THREE, a lipid based approach to assemble nanoparticles into well-defined three-dimensional superstructures is developed where lipid molecules form a crystalline matrix in which nanoparticles are assembled. This approach allows one to use the lipid framework to dictate the shape of the nanoparticle superstructures such that one can realize octahedra, truncated octahedra, cuboctahedra, and cubes with micrometer and sub-micrometer dimensions. Mechanistic insight into this lipid-guided approach reveals a three-stage process that is driven and directed by the self-organization of lipid molecules.;In CHAPTER FOUR, a synthetic molecular system based upon porphyrazine is developed, in which porphyrazine macrocycles are functionalized with different numbers of alkanethiol pendant groups and fused benzo moieties at specific locations on the periphery of the macrocyclic structure. This system allows one to control how these molecules self-assemble on a gold surface through molecular design such that one can realize 'standing up', 'crouching', and 'lying down' orientations of pz monolayers with the average film thickness ranging from ∼3-12 A.;Built upon the molecular system developed in CHAPTER FOUR, CHAPTER FIVE describes a systematic study of the heterogeneous electron transfer thermodynamics of a series of functionalized freebase and metal-coordinated porphyrazine monolayers as a function of the monolayer thickness, charge distribution, and solvent environment. This study reveals that upon surface adsorption the reduction potential of a porphyrazine shifts significantly from its formal potential when free in solution. The magnitude of the potential shift is strongly dependent on the molecular orientation of the monolayer. In addition, the potential shift is a continuous function of and reversely related with the distance of the electroactive porphyrazine macrocycle from the electrode surface. Furthermore, at a short molecule-electrode distance (∼3 A), the charge distribution within the porphyrazine macrocycle also play a role in determining the reduction potential shift.