A Study of the Effects of the Addition of Halogen on the Redox Potentials of Several Sensitizing Dyes

Basic data are lacking in the literature concerning the reactivities of desensitizing dyes to Iodine, and concerning their redox potentials while undergoing such reactions. Such information may be useful in deciding on the mechanism of desensitization, since there is good evidence that the halogen liberated from an Iodobromide emulsion during photolysis is actually Iodine. Therefore, experiments were undertaken to measure the polarographic anodic potential of the first addition product of a series of thiacyanine dyes, if such a species existed. Also, preliminary experiments were undertaken to determine the relative reactivities of the dyes to molecular Iodine and Bromine while they were adsorbed to a dilute Silver Bromide sol. Both experiments proved unfeasable because, first, it was not possible to achieve a stable sol for the purpose of spectrophotometry, and second, the dyes did not show a stable, reactive intermediate. However; basic data concerning the relative reactivities of the dyes to Iodine and Bromine were obtained. The dyes prove to be at least as reactive to Iodine as they are to Bromine, and the reactivities to both halogens increased with increasing chain length by orders of magnitude. There was no evidence of dye regeneration nor of equilibrium with the halogen.