Abstract
Pinacyanol is a dye belonging to the cyanine group. During the last 10 years great advances have been made, chiefly by Mills 1 and his coworkers, in the preparation and elucidation of the chemical constitution and photographic properties of the cyanine dyes. There are about 37 different types of cyanine dyes known.
The cyanine dyes have the peculiar property of conferring extra sensitiveness on silver halides, which are only sensitive to the blue and violet regions of the spectrum. If the proper dyes are added to the emulsion, or if the films are bathed in the solution, they become extremely sensitive to red, yellow, orange, green and to the invisible infra-red portions of the spectrum. This sensitizing property is probably due to the following characteristic molecular grouping present in all sensitizing cyanine dyes:
The cyanine dyes are strongly basic dyes, the monoacid salts are colored while the diacid salts are colorless. The chemistry of the sensitizing action is unknown. However, we do know that the dye is adsorbed by the silver halide.
The cyanine dyes∗ available commercially are: Orthochrome T (sensitizer for green), Pinacyanol (sensitizer for red), Kryptocyanine (sensitizer for extreme red), Dicyanine A (sensitizer for infra-red), Neocyanine (sensitizer for infra-red) and Quinoline blue.† These dyes, with the exception of quinoline blue have not been used for histological purposes. The staining properties were investigated for various tissues. Pinacyanol was the most satisfactory, not only as a polychromatic stain cat exogen but also for its quick staining action. Naphtocyanol and Dicyanine A were less satisfactory but may be used for special purposes. Kryptocyanine and Orthochrome T stained diffusely without differentiation. Neocyanine had no staining effect at all.
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