Chemical structure, spiropyran

SchemelO Chemical structure ofthe polypeptide obtained after introducing spiropyran units into the side chains of succinylated poly(L-lysine) (XVII). 70 ...

FIGURE 3.14 Chemical structures and isomerization of (top) diarylethene and (bottom) spiropyran isomers. 

Fig. 4 Chemical structures of the 11-cis retinal (a), p-hydrojdcynnamoyl anion (b), azobenzene (c), and spiropyran-merocyanine systems (d). The bond thatisomerizes after absorption of light in the first three molecules and the photo-induced reaction in the latter system are shown.

Photoresponsive systems are seen ubiquitously in nature, and light is intimately associated with the subsequent life processes. In these systems, a photoantenna to capture a photon is neatly combined with a functional group to mediate some subsequent events. Important is the fact that these events are frequently linked with photoinduced structural changes in the photoantennae. This suggests that chemical substances that exhibit photoinduced structural changes may serve as potential candidates for the photoantennae. To date, such photochemical reactions as E/Z isomerism of azobenzenes, dimerization of anthracenes, spiropyran-merocyanine interconversion, and others have been exploited in practical photoantennae. It may be expected that if one of these photoantennae were adroitly combined with a crown ether, it would then be possible to control many crown ether family physical and chemical functions by means of an ON/OFF photoswitch. This is the basic concept underlying the designing of photoresponsive crown ethers. We believe that this is one of the earliest examples of molecular machines . 

Many recent papers are ignored or mentioned only briefly because they are discussed elsewhere in this book. The biological applications of spiropyrans incorporated into membranes and their use as specific ion recognition sensors and signal transducers is discussed in Volume 2, Chapter 9. Spiropyran-modified artificial monolayer, bilayer, and multilayer membranes whose physical and chemical properties can be controlled by irradiation are discussed in Chapter 1 in Volume 2. The X-ray structures of numerous spiropyrans, the nature of the molecular packing, and the relationship between structure and photochemical behavior is reviewed in Volume 2, Chapter 7. 

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