Molecular chemically controlled switch

Besides these vast pharmaceutical applications, they are also of use as building blocks for the synthesis of organic semiconductors, dyes, rigid subunits of macrocyclic receptors, and chemically controllable switches [9-12], The prominent place of benzimidazoles in organocatalysis and materials chemistry is due to two reasons stemming from their molecular architecture (1) the imidazole is a precursor to N-heterocyclic carbenes (NHCs) and (2) the benzene ring provides a convenient moeity to which additional functionality may be easily added to modify the spatial and electronic characteristics of a benzimidazole derivative. 

Figure 6.7 A chemically controllable molecular shuttle. The macrocydic ring can be switched between the two stations of the dumbbell-shaped component by acid-base inputs.

Redox and Chemically Controlled Molecular Switches and Muscles... 

So far, several example of the chemically and electrochemically controlled switching of bistable linear molecular machines have been presented. The final section of this chapter will be dedicated to illustrating how such molecular switches and motors, when designed ingenuously, can also be powered by nature s most abundant and powerful energy source - light. 

Fig. 3 A chemically controllable molecular shuttle the macrocyelic ring can be switched between the two stations of the dumbbell-shaped component by base/acid inputs. Additionally, in the deprotonated rotaxane, the ring can be displaced from the bipyridinium station through reduction of such unit. (View this art in color at www.dekker.com.)...

Metallophthalocyanine polymers offer good stability in thermal, chemical, hydrolytic and photochemical environments. The reversible redox property and cycle stability of phthalocyanine compounds and their polymers make them useful as active components in sensors, switches, diodes, memory devices, NLO materials, etc. different types of phthalocyanine polymers are available and they are amenable to chemical modifications to suit the devices requirements. It is possible to exercise chemical control of the properties of the phthalocyanine polymers as well as functionalize other conducting polymers with the characteristics of phthalocyanines. Hence phthalocyanine polymers have become potential candidates for producing useful and viable materials for electronic, optoelectronic and molecular electronic applications. 

Another synthetic strategy is based on self-assembly driven by molecular recognition between complementary 7t-donors and 7T-acceptors. Examples include the synthesis of catenanes and rotaxanes that can act as controllable molecular shuttles (6,236). The 7t-donors in the shuttles are located in the dumb-bell shaped component of the rotaxane and the 7T-acceptors in the macrocydic component, or vice versa. The shuttles may be switched by chemical, electrochemical, or photochemical means. 

Switching systems based on photochromic behavior,I29 43,45 77-100 optical control of chirality,175 76 1011 fluorescence,[102-108] intersystem crossing,[109-113] electro-chemically and photochemical induced changes in liquid crystals,l114-119 thin films,170,120-1291 and membranes,[130,131] and photoinduced electron and energy transfer1132-1501 have been synthesized and studied. The fastest of these processes are intramolecular and intermolecular electron and energy transfer. This chapter details research in the development and applications of molecular switches based on these processes. 

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. 

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