Molecular Design and Supramolecular Assemblies of Novel Amphiphiles with Special Molecular Structures in Organized Molecular Films

Abstract

It is well known that supramolecular chemistry has played a major role in progressing research in nanoscience and nanotechnology, leading to novel classes of materials which are capable of light or electrically stimulated chemistry and long-range organized assembly (Lehn, 1995). Interfacial supramolecular assemblies use well-characterized amphiphiles as building blocks to create assemblies on surfaces that are purposefully structured on the molecular level, while at the same time extending over supramolecular distances (Kuhn et al., 2000). Creating organized structures is an important goal in interfacial supramolecular chemistry. The Langmuir-Blodgett technique is important for the production of macroscopic materials that are organized on the molecular length scale. This approach allows amphillic molecules to be oriented at the air-water interface and then transferred sequentially onto a solid support. The flexibility of molecular design is one of the most significant advantages of supramolecular assembly, allowing organic, inorganic and biological components to be used as building blocks. Organized molecular films deposited on solid surfaces are of great conceptual interest because their small thickness makes them ‘quasi-ideal’ two-dimensional systems. They constitute a novel ‘bottom-up’ approach to creating nanoscale structures. This approach contrasts with ‘top-down’ approaches that entail making existing devices so small that they eventually finish up as nanosized objects, with dimensions of no more than a few hundred nanometers. On the other hand, amphiphiles are organic molecules that have the ability to adsorb at interfaces, thereby altering significantly the physical properties of those interfaces. Numerous variations are possible within the structure of both the head and tail group of amphiphiles (Holmberg, 1998). The head group can be charged or neutral, small and compact in size, or a polymeric chain. The tail group is usually a single or double, straight or branched hydrocarbon chain, but may also be a fluorocarbon, or a siloxane, or contain aromatic groups. Since the hydrophilic part normally achieves its solubility either by ionic interactions or by hydrogen bonding, the simplest classification is based on amphiphile