Abstract

Spectral sensitizing dyes extend the responses of imaging materials to blue, green, red, and near infrared wavelengths. The most useful classes of dyes for photographic (silver halide) imaging are cyanine and merocyanine dyes, which provide excellent spectral sensitizing efficiencies, highly color-selective (narrow, aggregated) absorption bands, and suitable solubility for handling during manufacturing and photographic development. Extensive industrial libraries of these compounds provide well-tested synthetic pathways that are useful in tailoring dye structures for other applications. Electrophotography utilizes thiapyrylium dyes, squaraine dyes (analogs of merocyanines), or phthalocyanines to spectrally sensitize photohole conduction in colorless organic polymers. Red and infrared spectrally sensitized chemical reactions in medicine (eg, photodynamic therapy) use long-wavelength dyes of the merocyanine, phthalocyanine, and hematoporphyrin classes. Spectral sensitizers from several dye classes either sensitize photochemical reactions or cause material degradation, especially those that interact to give high yields of singlet oxygen.