Molecular-level switching

Keywords Luminescence m Fluorescence m Phosphorescence a Sensors a Switches a Logic Gates a Supramolecular Systems a Truth Tables a Photoinduced Electron Transfer a Molecular-Level Devices... 

In this chapter, we will discuss the recent results regarding the development of molecular switches and logic gates toward information processing at the molecular level based on electroactive molecules and supramolecules. Also, we will illustrate the progress of application of electron donor-acceptor compounds in high-density information storage. 

Such a stationary minimum on the distribution curve has tentatively been ascribed by Kurbatov et al. to a pre-ionization process from a high excited molecular level, situated near the first-excited leyel of the ion. The neutral excited molecule M could switch, during its lifetime, to the state M+ + e (process 3 in Section III). This suggestion is, however, doubtful, since it implies that the excitation of the molecule to a higher state decreases the probability of the direct transitions to the ionized state. For benzene, o-, m-xylene, mesitylene, and durene, when the photons exceed Ip by 2.3-2.6 e.v., new sharp maxima of slow electrons appear. 

Electrons switch between levels characterized by Ms values. Let us examine now an ensemble of n molecules, each with an unpaired electron, in a magnetic field at a given temperature. The bulk system is at constant energy but at the molecular level electrons move, molecules rotate, there are concerted atomic motions (vibrations) within the molecules and, in solution, molecular collisions. Is it possible to have information on these dynamics on a system which is at equilibrium The answer is yes, through the correlation function. The correlation function is a product of the value of any time-dependent property at time zero with the value at time t, summed up to a large number n of particles. It is a function of time. In this case the property can be the Ms value of an unpaired electron and the particles are the molecules. The correlation function has its maximum value at t = 0 since each molecule has one unpaired electron, the product of the... 

For instance, the [2]catenane, 51 [112] has been synthesized incorporating an anthracene subunit—an important electrochemical and photochemical active site which is a major building block required for switches and machines at the molecular level. The bulky anthracene stops the normal dynamic circumrotation... 

The relative movements of the interlocked components of a [2]catenane and of a [2]rotaxane can be exploited111 121 to perform switching operations at the molecular level. Indeed, there are two states associated with a [2]catenane (Figure 2a) incorporating two different units (0 and 1) in one of its two macrocyclic components. In State 0, the unit 0 is located inside the cavity of the other macrocyclic component and the unit 1 is positioned alongside. In State 1, the unit 1 is located inside and... 

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