Devices molecular switch

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. 

Delonno E, Tseng HR, Harvey DD, Stoddard JF, Heat JR (2006) Infrared spectroscopic characterization of [2]rotaxane molecular switch tunnel junction devices. J Phys Chem B 110 7609-7612... 

Fig. 7 A molecular switch made of the leg of a legged Cu-porphyrin adsorbed on a Cu(211) surface, (a) An idealized version of such a molecular switch where the switching leg is exactly interconnected to two atomic wires in a Fig. la like configuration. The device resistance is maximum for a perpendicular = 0 conformation, (b) The real experimental device where the STM tip apex can be maintained at 0.7 nm or 0.9 nm separation between the tip and the surface in between the leg switching. In this case, the resistance is minimum for perpendicular to the Cu(211) surface = 0 conformation. The energetic of the switching mechanism can be calculated and the switching barrier height was also determined experimentally...

Figure 14. An orthogonally-fused system that could act as a molecular switching device.

Keywords Molecular Devices a Molecular Machines a Molecular Wires a Antenna Systems a Molecular Switches a Plug/socket Systems a Pseudorotaxanes a Rotaxanes a Catenanes a Supramolecuiar Chemistry a Photochemistry a Electrochemistry a Luminescence... 

Let us consider molecular switches based on intramolecular electronic transition. Generally, transfer of energy or an electron within a molecule proceeds in femtoseconds. The aim is to produce molecular electronic devices that respond equally rapidly. Molecular switches that employ optically controlled, reversible electron-transfer reactions sometimes bring both speed and photostability advantages over molecular switches which are usually based on photochemical changes in their molecular structure. Important examples are the molecnlar switches depicted in Scheme 8.3 (Debreczeny et al. 1996). 

Since electrons are of rather low mass, PET rates can be extremely fast with transit times in the ps-ns range. Molecular switches where the only moving part is an electron are likely to be much faster than those involving nuclear motion. Since they require ion movement, photoionic devices based on PET will operate at slower rates. However these are fast enough compared to the human timescales. 

Introduction of an azabenzene unit into the surfactant backbone permitted light-induced cis-trans rearrangements. A change in conductivity accompanied the cis-to-trans transition. Thus, these LB films offer a basis for the construction of molecular switching devices (Fig. 120) [743-745],... 

These environmentally sensitive gels are being extensively studied and applied to a variety of fields in medical science, engineering, ecology, food science, drug delivery systems, chemo-mechanical and electro-mechanical actuators, switching devices, molecular sieves, chemical re-collecting retainers, and so on. These aspects are not covered in this issue. The reader may consult some of the references [1,8]. 

The great variety of incorporable building blocks also offers the synthetic chemist many potential structural and functional design possibilities. The insertion of, e.g., photo-responsive elements, groups with further supramolecular derivatization potential, or sulfonamide units which enable subsequent inter- and intramolecular linkage of catenanes and rotaxanes might render good service in the development of molecular switches [64] and devices [65]. 

Addition of potassium ions to the fibers leaves the fibrous structure intact but destroys the helicity [128]. Sandwich complexes between the cation and 114d are observed. With higher concentrations of potassium, the sandwich complexes break down and isolated 4K+114d are observed (Scheme 61). In both complexed forms the salt blocks the chirality transfer from the side chains to the supramolecular assemblies. Such fibers with controllable chirality can be interesting materials for molecular switches or in sensors devices. 

Within the context of supramolecular devices, re-emission of the radiation by luminescence is of interest in sensing and signalling applications, while chemical reactions are of interest in applications such as molecular switches and photocatalysis. Strictly speaking absorption and re-emission type processes are termed molecular photophysics while light-induced chemical reactions or chemical processes are termed photochemistry . 

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). 

Kawai, S. H., Gilat, S. L., Lehn, J. M., Dual-Mode Optical-electrical molecular switching device. J. Chem. Soc., Chem. Commun. 1994, 1011-1013. 

Theoretical chemistry at York University was strengthened in the 1990s with the appointments of Bill Pietro in 1991 and Rene Fournier in 1996. Pietro wrote part of the Gaussian code as a graduate student and several modules of SPARTAN while an assistant professor at the University of Wisconsin. While he was in Madison he developed a research program based on molecular electronic devices.236 He expanded his interests to several facets of molecular electronics, including molecular electroluminescent materials, molecular electronic devices (diodes, switches, and sensors), and functionalized semiconductor nanoclusters.237 These new materials not only are scientifically very exciting, but they offer the possibility of revolutionary impact on the future of the electronics industry. 

Balzani, V., Venturi, M., Credi, A. Molecular Devices and Machines. A Jorney into the Nanoworld, Wiley-VCH, Weinheim, 2003 b) Feringa, B.L. (ed.), Molecular Switches, Wiley-VCH, Weinheim, 2001 c) Raehm, L., Sauvage, J.-P. Molecular machines and motors based on transition metal-containing catenanes and rotaxanes, Struct. Bond. 99 (2001), 55-78. 

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