The chemistry of the most important dyes and pigments used in the coloration of traditional substrates, including textiles, paints, printing inks and plastics, has been dealt with extensively in the previous chapters of this book. It is likely that this range of well-established products will remain for the foreseeable future as the most important materials manufactured for the purpose of providing colour. In recent decades, there is no doubt that new products for such conventional applications have appeared with reduced frequency as industry has concentrated research effort on process and product improvement, and addressing a range of environmental issues (Chapter 11). However, in the same period, there have been exciting developments in organic colour chemistry as a result of the opportunities presented by the emergence of a range of novel applications which place significantly different demands on dyes and pigments. These colorants have commonly been termed functional, because the applications in question often require the dyes or pigments to perform certain functions beyond the simple provision of colour. Alternatively, they may be referred to as high technology colorants, because they are designed for use in applications derived from advances in fields to which this particular term commonly refers. The applications of functional dyes and pigments include a wide range of electronic applications, including liquid crystal displays, microfilters, solar energy conversion, lasers and optical data storage, some of the more recently developed reprographic techniques, such as electrophotography and ink-jet printing, and a range of biomedical uses. While these colorants...