Molecular electronics monomolecular

The goal of molecular physics is to find molecules which can carry out various functions in a molecular electronics, e.g. as switching elements or as conductors ( molecular wires ). The required molecular properties are described in the book by Haken and Wolf, Molecular Physics and Elements of Quantum Chemistry, Chap. 22 [1] and here, briefly, in Sect 12.2. In monomolecular molecular electronics, one makes use of single molecules or isolated functional units to carry out electronic functions. These molecules must be coimected to other units of the device. This type of molecular electronics in the narrow sense is not the subject of this book, which is instead concerned with the sohd state. 

The above statements are valid for monomolecular layers only. In the case of polymer films with layer thickness into the p-range, as are usually produced by electropolymerization, account must also be taken of the fact that the charge transport is dependent on both the electron exchange reactions between neighbouring oxidized and reduced sites and the flux of counterions in keeping with the principle of electroneutrality Although the molecular mechanisms of these processes... 

Under optimal conditions this layer can be transferred to a solid substrate (glass or metal) and several monomolecular layers can be deposited in this way. These L-B films represent highly organized molecular assemblies on a macroscopic scale, since not only the distance between neighbouring molecules but also the relative orientations of their chromophores can be determined. The distance dependence of photoinduced energy and electron transfers have been investigated in L-B films. The R6 dependence of the Forster dipole-dipole mechanism has been confirmed, but it must be realized that some questions remain concerning the possible role of defects in the film structures. 

Excited-state relaxation can proceed spontaneously in monomolecular processes or can be stimulated by a molecular entity (quencher) that deactivates (quenches) an excited state of another molecular entity, by energy transfer, electron transfer, or a chemical mechanism [lj.The quenching is mostly a bimolecular radiationless process (the exception is a quencher built into the reactant molecule), which either regenerates the reactant molecule dissipating an energy excess or generates a photochemical reaction product (Figure 4.1). 

So there you are. I find it difficult to chose between my projects. Since you are an electron diffractionist what you probably think of first is my early treatment of the effects of anharmonicity of molecular vibrations on analyses of molecular structures. This was reviewed in detail in the prefatory chapter you and your husband solicited. Surface chemists might think my invention of an ellipsometric technique to measure absorption spectra of films as thin as monomolecular might qualify as the most important. Since I was too poor to do electron diffraction work, I constructed some ellipsometers during my early years at Iowa State and discovered their unique capabilities. 

An attractive approach to solving the mass transfer limitations of these investigations is to immobilize the electroactive species at the electrode surface within a monomolecular film. Clearly, if the electroactive species is immobilized at the electrode surface, diffusion of the species to the electrode does not need to occur prior to electron transfer. In addition, immobilization at an electrode surface can preconcentrate the species of interest, resulting in higher currents that are easier to detect. Electroactive adsorbed monolayers have been developed that exhibit close to ideal reversible electrochemical behavior under a wide variety of experimental conditions of timescale, temperature, solvent, and electrolyte. These studies have elucidated the effects of electron transfer distance, tunneling medium, molecular structure, electric fields, and ion pairing on heterogeneous electron transfer dynamics. 

Molecular recognition between biomolecules is another strategy that has been used to deposit assemblies of redox enzyme on electrodes. It has led to the construction of true monomolecular layers and of spatially defined multimonomolecular structures. The dynamics of these systems has been fully characterized and the activity of the deposited enzyme tested quantitatively, which has been very seldom the case with the systems depicted in the preceding text. For this reason, the following sections focus on these structures. Besides describing the construction procedures, emphasis is laid on the detailed analysis of the catalysis responses and on the mechanisms it allows one to uncover. As a prelude to such kinetic analyses, the catalytic responses of a redox enzyme with a one-electron mediator in solution are first examined. 

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