Molecular memory element

A stereospecific photochemical switching process provided a useful basis for chiroptical molecular switches and molecular memory elements (07CC1745). 

Pina, F., Maestri, M., and Balzani, V., Photochromic systems based on synthetic flavylium compounds and their potential use as molecular-level memory elements, in Handbook of Photochemistry and Photobiology, Abdel-Mottaleb, M.S.A. and Nalwa, H.S.Eds., American Scientific Publishers, Stevenson Ranch, 2003, 3, 411. 

An interesting futuristic application is in the field of molecular electronics where a one-dimensional molecular wire such as polyacetylene in combination with a suitable molecular switch, e.g. salicylideneanilines, would yield a molecular microchip whose information storage capacity would be about 10 times that of a conventional microchip. A new generation of high performance computer with memory elements of nanometre dimensions is visualized on the basis of such molecular microchips. 

In principle any molecule able to exist in two reversible, switchable states can represents a molecular switch (bistable device) with potential to form part of molecular circuitry or act as molecular memory. An excellent component for switchable molecular devices is the 1,2-dithienylethene system, which has been exploited ingeniously by Lehn in a number of bistable systems.54 The core switching element is the transformation of the dithienylethene unit between two stable states as a function of the wavelength of incident radiation (Scheme 11.8). 

Information technology has revolutionized daily life in the last decades and the continuously increasing amount of data to be stored and manipulated strongly stimulated the search for switching and memory elements as tiny as a single molecule. Molecular switches can be converted from one state to another by an external stimulus such as light, electricity or a chemical reaction. Like with their macroscopic counterparts, one is able to control numerous functions and properties of materials and devices. 

It is possible to encode an enormous amount of amplitude and phase information into a short pulse of electromagnetic radiation. The pulse can be designed to direct the intra-molecular dynamics toward an a priori specified target state, the pulse can be modified empirically based on some sort of learning algorithm to maximize a desired dynamical outcome (e.g., a specified photofragment) (Judson and Rabitz, 1992 Bardeen, et al., 1997 Feurer, et al., 2001 Rice and Zhao, 2000 Levis, et al., 2001 Weinacht, et al., 2001 Levis and Rabitz, 2002), or the pulse can be tailored to create a F(t) in which the amplitudes and phases of individual electronic or rotation-vibration eigenstates could be used as a multibit memory element in a quantum computer (Ahn, et al., 2000 Ballard, et al., 2002). 

Fig. 15.5. Collective phenomena, (a) The domino principle. An energy cost corresponding to unglueing and knocking down the dominoes, (b) Hypothetical electronic domino (or nmemon - an element of molecular memory) composed of electron donors (D) and electron acceptors (A). In order to transfer the first electron we have to pay energy A. The second electron transfer (when the first is alreatfy transferred) needs less energy, because it is facilitated by the dipole created. The transfer of the third and further electrons does not need any energy at all (the energy actual decreases). The hypothetical electronic domino starts running (L.Z. Stolarc k, L. Piela, Chetn. Phys. 85 (1984) 451).

First step towards synthesizing reversible molecular switches, and integrating these switches into an electronic circuits, had been done pioneered by Rotaxane-based-technology developed by HP. Any digital microelectronic device is based on memory elements and switches, set up as capacitors, diodes and transistors. Complex elements, such as bi-stable flip-flops, are created from these simple elements combining e.g. two transistor to set up a Schmitt trigger. 

The interest in interference effects in cross-conjugated molecules arose from molecular electronics. The chemist s vision of molecular electronics consists of chemically tailored circuits, where the electronic function is controlled by carefully designed substituents. This requires more than molecular wires it requires functions such as memory elements, switches, logic elements, and gate dielectrics. In short, it requires polarizable but nonconducting elements. In many of these cases, an ofT state is required in addition to the on state. Sometimes there is a requirement for fast switching between these states, and at other times long-term stability of either the on or oflT state is needed. 

TomizaM K-y, Mihara H (2007) Phosphate-mediated molecular memory driven by two different protein kinases as information input elements. J Am Chem Soc 129 8345-8352... 

Protic tautomerism [1], which involves reversible intramolecular transfer of protons, usually between electronegative atoms, is an important feature not only of biologically relevant heterocycles [2] but also of a variety of potentially useful synthetic systems [3]. For instance, several current research themes involve the study of tautomeric processes as memory elements or as molecular switches with a view to developing future molecule-scale devices [4, 5]. 

In order to carry out sophisticated computation the molecular computers of tomorrow will need not just basic elements such as switches, memory and connectors but also more sophisticated components, particularly logic gates. A logic gate is an element of a computer that gives a particular output for a... 

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