Applications of Photochromic Materials

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). 

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... 

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... 

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. 

A crucial point that must be addressed concerns the thermal stability and the fatigue phenomenon observed in the chromophores. It is a fact that many photo-chromic compounds are irreversibly degraded upon long exposure to light, thus limiting their use for various applications. Major advances in the preparation and performance of photochromic materials have been made in the past five years. Irie et al.11271 have recently developed new photochromic compounds, 1,2-diarylethenes, which display photochromic behavior with unchanged intensity even after 104 coloration decoloration cycles. 

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

The way that the photochromic material is incorporated into the lenses is of importance for the commercial application of these materials. This can be achieved by injection-moulding in a thermoplastic or precursor monomer or resin system, surface coating, diffusion into lens surfaces (imbibition) or formation of... 

Applications of these materials are oriented toward the development of hybrid photochromic films for waveguides [87], high refraction index for LED encapsulation [283], or materials showing holographic as well as photorefractive properties [284]. 

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