Supramolecular assemblies dimensions controlled

Recently, many scientists and engineers have looked for methods to control the sizes of QDs and make possible the formation of ordered lateral two-dimensional superlattices or vertical superlattices for heterojunction thin films. One approach is the top-down method, molecular beam epitaxy nanolithographic technology, which has been developed with the development of microelectronics and processing techniques for traditional inorganic semiconductors. This technique of nanoscale manipulation can reach only the upper limits of sizes defined by nanostructure physics, and has successfully manipulated artificial atoms and molecules [10-12). Bottom-up method is based on molecular and supramolecular assembly techniques that have been proposed by chemists in recent years. With this method, it is possible to prepare monodispersed defect-free nanocrystal QDs 1-10 nm in size and to control easily QDs coupling to form nanocrystal molecules, even quantum dot superlattices in two or three dimensions. 

This chapter describes supramolecular assemblies in mesoscopic dimension and their recent developments. It also compliments earlier reviews [21,22]. The mesoscopic supramolecular assemblies are defined as hierarchically self-assembled amphiphilic supramolecular structures whose ternary and the higher assembly structures are controlled through solvophilic-solvophobic interactions. Here, pairs of molecules brought by secondary interactions are designed that acquire amphiphilicity upon complexation. They become units of self-assembly and hierarchically grow into mesoscopic-scale supermolecules that are dispersed stably in aqueous or in organic media. 

Dramatic advances in molecular synthetic chemistry have led to a high level of control over molecular interactions. However, we are only at the beginning of a more extended design of chemical interactions in two and three dimensions. If we learn how to control the structure, properties, and stability of desired supramolecular assemblies, many areas in materials science and technology, such as microelectronics, optics, sensors, and catalysis, will benefit substantially. Representative areas of research activity include selective monolayer assemblies on electrode surfaces functionalized pillared layered materials and assemblies of conductors, semiconductor clusters, or nonlinear optical materials in three-dimensionally ordered hosts such as zeolites. 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

The design and synthesis of supramolecular architectures with parallel control over shape and dimensions is a challenging task in current organic chemistry [13, 14], The information stored at a molecular level plays a key role in the process of self-assembly. Recent examples of nanoscopic supramolecular complexes from outside the dendrimer held include hydrogen-bonded rosettes [15,16], polymers [17], sandwiches [18, 19] and other complexes [20-22], helicates [23], grids [24], mushrooms [25], capsules [26] and spheres [27]. 

In contrast to the rod-coil diblock copolymer consisting of perfectly monodisperse rods, the liquid crystalline morphologies of rod-coil diblock copolymer containing polydisperse rods seem to be studied in less detail. In certain cases, the polydisperse nature of the rod-segments could hinder self-assembly into regularly ordered supramolecular structures. However, due to relatively simple synthetic procedures, liquid crystalline polymer can be of benefit for new materials with controlled internal dimensions ranging from the nanometer to macroscopic scale. 

The concept of "machine," which is so familiar in our macroscopic world, can be extended to the molecular level."] A molecular-level machine can be defined as an assembly of a discrete number of molecular components (i.e., a supramolecular system) designed to perform mechanical-like movements under the control of appropriate energy inputs. Molecules have nanometer dimensions and are the smallest entities exhibiting well-defined structures and shapes. Therefore, molecular-level machines represent the ultimate limit of miniaturization of the mechanical-machine concept. 

The generation of one-dimensional structures is of interest in a number of different areas, not least in that of molecular electronics and sensors, as reviewed in another contribntion in this section (see Self-Assembly of Supramolecular Wires, Self-Processes) Here, representative examples are shown in order to illustrate the preparation of fibers, the length of which is not controlled, but with the lateral dimensions being limited by a template, in order to confine the growth and thereby generate novel properties. 

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