Molecular motors light-powered

Figure 12.18 Schematic representation of a linear motor powered by light Adapted from V. Balzani, A. Credi and M. Venturi, Light-powered molecular-scale machines , Pure and Applied Chemistry Volume 75, No. 5,541-547 International Union of Pure and Applied Chemistry IUPAC 2003...

Credi A. Artificial molecular motors powered by light. Aust J Chem 2006 59 157-69. 

For a report of a light-powered molecular motor, see Koumura N, Zijlstra RWJ, van Delden RA, Harada N, Feringa BL (1999) Nature 401 152... 

Furthermore, just as photochemistry is a clean way to cause a reaction, it may offer a clean way to cause a movement in a macroscopic object. As a matter of fact, this is an issue rarely adopted by natme, where direct conversion of light into mechanical energy is limited to a few cases in bacteria [16]. This does not preclude adopting this principle for artificial system. As an example, one may think of controlling and directing the Brownian motion of molecules in solution and to induce directional translational and rotary motion of molecules or of nano-objects. In other words, rotary and translational motors may be devised and used to power future nanodevices. For example, rotary molecular motors allow the transmission of motion in multicomponent systems as well as reaching out-of-equilibrium assemblies (see Fig. 11.5) [18]. 

Figure 3. Feringa s second-generation light-powered molecular motors.

Nobel Laureate Jean-Marie Lehn has conceptually reduced the light-powered motor to a very simple system the chiral imine (Figure 4) 25). As observed for chiral alkenes, absorption of a photon produces out-of-plane rotation of the tt bond in imines. Molecular asymmetry should cause the 90 rotation to occur with some preference for clockwise or coimterclockwise direction. Photoisomerization of the anti imine to the syn geometry constitutes directional, 180° rotation. At room temperature, the syn isomer would rapidly undergo in-plane inversion to the original anti form. This brilliant simplification of the molecular motor based on photochemical/thermal cycling has not yet been experimentally reduced to practice. 

Figure 4. Lehn s putative light-powered chiral inline molecular motor. (Reproducedfrom reference 25. Copyright 2006 John Wiley Sons, Inc.).

Alcohol (3R,4R)-(- -)-31 (entry 19) is a starting material for the synthesis of a light-powered chiral molecular motor [CD( )237.2]-( )-44a, which rotates in one rotational direction by the use of hght energy as shown in Figure 55.10, where cis-olefin [CD( )238.0]-44c is one of the motor rotation isomers.As these compounds take twisted structures, their ACs or hehcities are defined as (P,P) or MM)-... 

FIGURE 55.10. Synthesis of a light-powered chiral molecular motor 44a and determination of its... 

FIGURE 55.11. Synthesis of a new light-powered chiral molecular motor 48a and X-ray stereostructure of racemate ( )-48a. 

Fujita T, Kuwahara S, Harada N. A new model of light powered chiral molecular motor with higher speed of rotation (1). Synthesis and absolute stereostructure. Eur. J. Org. Chem. 2005 4533 543. 

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. 

The biaryls are useful in rational designing functional molecules and materials. The large steric hindrance and the semirigid structure with restrict rotation provided various functional biaryls, such as arylporphyrins [162,170], molecular-scale motors rotate by chemical power or light [73,163], a photoswitchable electron transfer aromatic compounds for the design of molecular photonic devices [171,172],a stable thioaminyl radicals [173],phenylnitroxide-substitut-ed Zn(II) porphyrins [174], and polycyclic aromatic compounds [175-177]. 

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