Memory devices, molecular electronic

New natural polymers based on synthesis from renewable resources, improved recyclability based on retrosynthesis to reusable precursors, and molecular suicide switches to initiate biodegradation on demand are the exciting areas in polymer science. In the area of biomolecular materials, new materials for implants with improved durability and biocompatibility, light-harvesting materials based on biomimicry of photosynthetic systems, and biosensors for analysis and artificial enzymes for bioremediation will present the breakthrough opportunities. Finally, in the field of electronics and photonics, the new challenges are molecular switches, transistors, and other electronic components molecular photoad-dressable memory devices and ferroelectrics and ferromagnets based on nonmetals. 

For quite a few years we have been concerned with the use of molecular systems in memory devices. Whatever the final objective might be, a fundamental requirement for the system is to have an hysteresis effect with regard to a given perturbation. When it is so, a transition between two electronic states takes place for a certain value of the perturbation, /Vf, when the perturbation increases, and for another value of the perturbation, Pcl, when the perturbation decreases, with Pc[ < Pcf. Between those two critical values, the state of the system depends on its history or on the information which has been stored. It is of course well known that a hard magnetic material might be used for storing information. Our work provides evidence of the possibility that molecular chemistry might provide compounds of that kind. 

Memory devices (electrical, optical) Molecular electronics Nonlinear optics Packaging materials pH modulator Polymer/solid electrolytes Semiconducting devices p-n junctions, pho-tovoltaics, Schottky diodes, light-emitting diodes, transistors, etc. 

Fig. 33 A 160-kb molecular electronic memory device [236]. (a) Structural formula of the molecular switches used in the device.

Finally, with the aim of industrial applications, assembling the magnetic molecules onto various substrates is another important field, but one that has been less studied. The application potential of magnetic molecular materials in the manufacture of molecular based memory devices, quantum computing, and spintronics devices, requires an understanding of the interactions between the material and substrate in order to manipulate the spin and electronic states of the target system to realize the desired specific properties [137]. 

Polynuclear complexes, molecular dyads, triads, and other supermolecules composed of redox- and photo-active metal polypyridine units have a great promise as components of future molecular electronic or photonic devices as optical switches, relays, memories, etc. [38, 46],... 

There is no limit to the number of photochromic systems possible. The systems discussed are excellent candidates for integration into solid-state devices because nearly all retain their photochromic properties in the absence of solvent. The organization of these systems in tandem with other molecular systems is being pursued. For the switching applications many of these systems have much too slow a turnover rate to be explored as working devices. That is unless the connectivity in these systems can be increased. In the meantime, photochromic systems will probably be explored as possible optical memory devices. The most promising switches are those based on the much faster processes of electron and energy transfer. We will now examine research in these areas. 

The immobilization of a photoisomerizable material that can be switched by light between redox-active and redox-inactive or conductive and insulating states offers an encouraging route toward integrated molecular memory devices. Figure 7.2 shows a photoisomer state A in which the molecular unit is redox-inactive and no electronic signal is transduced. Photoisomerization of the chemical component to state B generates a redox-active assembly, and the electron transfer between the electrode and the chemical modifier yields an amperometric (electrochemical) indicator of the state of the system. 

Magnetic interactions of a paramagnetic metal center and a free radical ligand are of interest for the development of new types of molecular magnetic materials. Complexes of this type (such as (83)) change their magnetic properties upon irradiation by visible light and can serve as a basis for development of novel photo-activated memory units for electronic devices.346,347... 

If any systems we design are to operate as potential electronically controllable molecular-based memory devices, then they must show a similar hysteretic profile, except Magnetization has to be replaced by Current and External Magnetic Field by Voltage . 

Electron transfer in molecular memory devices 01MI55. 

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