Photochromic polymers applications

Polymer-based photochromic systems have been studied extensively and are attractive in terms of practical applications because of their advantages of stability and processability. A number of reviews and articles dealing with various aspects of photochromic polymers and photoactive biomaterials have been published. 68 Chiral photochromic peptides are discussed in Chapter 13, and photochromic liquid crystals and polymers for holographic data storage and nonlinear optics have been reviewed. 69 Specific stereochemical effects in chiral photoresponsive polymers include ... 

The occurrence of two different structures that can be interconverted through the agency of an external light stimulus can be the basis of a molecular switch. Moreover, when photochromic molecules are incorporated into polymeric compounds, their photoisomerization can affect the structure and the physical properties of the attached macromolecules. Therefore, photochromic polymers may be highly promising materials for application in optical technologies, as well as in the design of photoswitchable devices. 

J. Whittall, Fulgides and fulgimides— a promising class of photochromes for application, in Applied Photochromic Polymer System (C. B. McArdle, ed.), pp. 80-120, New York (1991). 

Applications or potential applications for these molecules have been demonstrated. Molecular switches can be built using supramolecular or LC photochromic materials.1 Photochromic polymers can be used in phototropic glasses or as a basis for information recording. IR-sensitive materials have been made using biphoto-chromic molecules. Light sensitive dental materials have been developed. 

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. 

We shall now embark on the main focus of this chapter photochromic azobenzene polymers and photochromic materials capable of undergoing photodimerization for potential use in optical data storage applications. Herein, the photochromic polymers described are those in which the photochromic molecule is covalently linked, either as part of the main chain or as a side-chain, to the polymeric system. 

K. Ichimura, Photochromic polymers, in J.C. Crano and R.J. Guglielmetti (Eds.), Organic Photochromic and Thermochromic Compounds. Volume 2 Physicochemical Studies, Biological Applications, and Thermochromism, Kluwer Academic/Plenum, New York, 1999, pp. 9-63. 

Although photochromic polymers are an important class of materials with many potential applications, and many excellent studies were devoted to this topic, recent... 

Photochromism is a reversible transformation of a single chemical species between two states, the absorption spectra of which are clearly different, the transition in at least one direction being induced by electromagnetic radiation [1], The widest and most important group of the photochromic system is based on electrocyclic reactions [2,3] a few have been commercially successful (polymer-based photochromic eyewear, novelty items and security printing inks). Several other photochromic systems based on E,Z-isomerization, cycloaddition reaction, electron or proton transfer have potential industrial applications [4],... 

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. 

The photochromic chromophores can be classified into two categories, depending on the thermal stability of the photogenerated isomers. When photogenerated isomers are unstable and revert thermally to their initial isomer state in the dark, the chromophores are classified as T-type (thermally reversible type). Most photochromic chromophores belong to this type. The photogenerated blue color of 6-nitro-l, 3, 3 -trimethylspiro-[2H-l-benzopyran-2,2 -indoline], for example, disappears in less than half an hour even in high Tg polymer matrices.181 Such thermally unstable photochromic chromophores cannot be applied in photoswitchable molecular systems, because the switched states are unstable. For those applications, the characteristic of persistence, or in other words thermal irreversibility, is indispensable. 

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