Applications of Photochromism

One successful application of inorganic photochromic systems has been in the manufacture of sunglasses. When a particular silver salt is incorporated in the lenses, the gjass will darken on exposure to sunlight in order to protect the eyes, but then bleach quickly when the light intensity drops, so that the same glasses can be used at night or indoors. 

The ds-trans isomerism of azobenzene has been incorporated in a novel chemical method for information storage at ultrahigh densities with nondestructive readout. A device based on this chemical information storage system would have, it is estimated, the capadty of 100 million bits per square centimeter. 

There also have been some investigations by the military directed toward developing camouflage photochromic paints.  

In most applications the ability of the system to undergo essentially endless recycling is an important factor. Thus, the degradation response time impacts heavily on the effectiveness of the system. In this regard, the valence bond tautomeric isomerizations would appear to possess the most promising properties, while those mechanisms that involve fragmentation open the 

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Obvious applications of photochromism include glasses which darken according to the intensity of the surrounding light, and such glasses have now been available for some time both in the form of plate glass for windows and in the form of lenses for sunglasses. Their action is very slow, it takes indeed many minutes for the photostationary state to be established. This is due to the fact that the photochromic effect takes place at the molecular level... 

Application of photochromic materials was first exploited by Alexander the Great. He designed a crude timepiece for his soldiers consisting of a chemically treated cloth worn on the left forearm. Under the action of the sun, the cloth changed colors each hour and provided Macedonian troopers with the world s first wristwatch. Among historians it is known as Alexander s Rag Timeband (8). 

The term photochromism can be defined as a light-driven reversible transformation between two isomers possessing different absorption spectra.111,21 The two isomers differ from one another not only in their absorption spectra, but also in their geometrical structures, oxidation/reduction potentials, refractive indices, and dielectric constants. When such photochromic chromophores are incorporated into functional molecules, such as polymers, host molecules, conductive molecular wires, or liquid crystals, the functions can be switched by photoirradiation.[3 61 Photostimulated reversible changes in refractive index can also be applied to optical waveguide switching.171 This chapter reviews applications of photochromic chromophores, especially diar-ylethene derivatives, in various photo switching molecular systems. 

Photochromism was first described in the scientific literature in 1876. 7 In his famous paper entitled The Photochemistry of the Future (1912), G. Ciamician19 discussed the importance of photochromic substances and mentioned the possibility of using such compounds for fashion purposes. Photochromism is also a natural phenomenon most biologic photoreceptors exhibit photochromic behavior. 101 Until the middle of this century research on photochromic compounds was mainly carried out in academic centers, but around 1960 it was recognized that this subject is also of considerable commercial interest and since then most of the research has been done in industrial laboratories. The applications of photochromic materials can been classified as follows 7 ... 

Another interesting possible application of photochromic materials is in the construction of new data storage systems for computers. For some time, researchers have been considering the possibility of... 

Practical applications of photochromism at first (ca. 1955-70) concentrated on the spiropyrans, and especially on BIPS compounds, because of their ready availability, photosensitivity, convenient thermal fade rates, and good color contrast when perceived by the human eye. However, applications in which the dye was required to cycle very many times (e g., an optical binary switch for a photochemical computer memory) or be irradiated continuously (e g., sunglasses, vehicle windshields) were impractical because of the rapid fatigue of these dyes.196... 

The application of photochromic materials for optical storage is the most important area, as discussed in Section 4.6.1. Many other applications have been developed, for example, nonlinear optical image processing,108 photoswitches,92... 

F. Matsui, H. Taniguchi, Y. Yokoyama, K. Sugiyama, and Y. Kurita, Application of photochromic 5-dimethylaminoindolyl fulgide to photon-mode erasable optical memory media with non-destructive ability based on wavelength dependence of bleaching quantum yield, Chem. Lett., 1994, 1869-1872. 

In relation to the perspective of application of photochromic quinones in optical recording media, the spectral characteristics of the photoinduced form for phenox-... 

Chapter 1 (Photochromic Polymers). Like most chemical reactions, photochromic reactions are influenced significantly by the media in which they occur. This chapter surveys the interactions between photochromic entities and polymer matrices in which they are incorporated either by binding them covalently to polymer backbones or by dissolving or suspending them in polymer solids. Polymeric materials play a very crucial role in studies on photochromism, particularly from a practical viewpoint since the various applications of photochromic materials invariably require that they possess definite forms like films, sheets, plates, fibers, beads, and so on, depending on the application. 

For any application of photochromic molecules, a discussion of the thermal stability of the colored form is in order. We will discuss two types of photochromic molecules (1) those that operate by a photon-heat mode (photochemical forward reaction and a thermal reverse reaction), such as spiropyran derivatives, and (2) those that exhibit a photon-photon mode, such as diarylethene derivatives. 

Molecular design and applications of photochromic crown compounds 03BCJ225. New trends in the chemistry of condensed azacrown ethers and azathiacrown ethers 03JHC1. 

Little AF, Christie RM. Textile applications of photochromic dyes. Part 1 establishment of a methodology for evaluation of photochromic textiles using traditional colour measurement instrumentation. Colouration Technol 2010 126(3) 157—63. 

Synthesis, Properties, and Applications of Photochromic Amorphous Molecular Materials and Electrochromic Polymers... 

Hampp, N. and T. Juchem, Fringemaker — the first technical system based on bacteriorhodopsin. In Bioelectronic Applications of Photochromic Pigments, 2000, lOS Press Szeged, Hungary. 

Little A. and Christie R. (2010), Textile applications of photochromic dyes. Part 2 Factors affecting the photocoloration of textiles screen-printed with commercial photochromic dyes. Coloration Technology, 126 pp. 164-170. 

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