Michael P. Filosa

Chapter 3 - Dyes used in Photography

Color photographic image dyes are formed as a function of silver development. Silver halide developing compounds reduce light exposed silver halide grains at a much faster rate than unexposed grains. The rate-determining step in dye formation is silver ion reduction. Dyes are also used to sensitize the silver to the required wavelengths of incident radiation, filter unwanted absorption, color correct the film, and protect the film from ambient light during development of the image. The requirements of color photography have created a vast arena for the creative chemist using mechanistic insights derived from physical organic chemistry to discover a seemingly endless series of ingenious inventions to produce the perfect image. This chapter provides an overview of the functional dye chemistry developed over the years for this field. To improve the performance and stability of dyes, especially at longer wavelengths, the concept of chain-stiffened infrared sensitizing dyes is introduced.