Dye-Bleaches

Nonmedical uses envisaged include as growth promoters, indicators for copying processes, analytical complexing agents, cyanine dyes and dye-bleaching catalysts. 

In the traditional silver halide dye-forming and dye-bleach processes, metal complex dyes are not normally used.62,63 However, metal complex azo dyes have been claimed15 for use in color diffusion transfer photography employing non-diffusible magenta dye-releasing dyes which, upon development of the silver halide layer, release a diffusible magenta dye (Scheme 7). 

The dye bleach process relies on the destruction of a uniformly dispersed dye in areas where exposure occurs. This results in a direct positive coloured image. The bleaching is... 

The first system which can be related to modem dye bleach materials was introduced in 1905 (05M111400), but it was not until the 1930s that manufactured products became available. 

The silver dye bleach reaction is very slow (65MI11401), and an additional agent is needed to promote the reaction between the immobile silver image and the immobile dye. 1,4-Diazines have been used as catalysts for this reaction, 2,3-dimethylquinoxaline (65), 2,3-diphenylpyrazine (66) and 2-hydroxy-3-aminophenazine (67) being specific examples. 

The cyan dye (71) (52USP2612448) and the yellow dye (72) (62GEP1137626), both derived from 2-pyrazolin-5-ones, have been suggested for use in dye bleach materials. 

Table 3. Dye bleaching with H2O2 and heterogeneous catalysts.

For a variety of arylsulfinate salts containing para-substituents of varying electron demand, it was shown under controlled polymerization conditions (1 M acrylamide monomer, pH 7, 4 x 10 3 M activator for methylene blue sensitization) (43b) that dye bleaching occurred with a quantum yield of 0.10-0.17 and that quantum yields for monomer loss were 1200-1700. The efficiency of the dye bleaching and the polymerization reaction increased as the electron donor ability of the sulfinate increased. ... 

Irradiation of films containing MB and the activators all resulted in polymerization, as judged by infrared spectroscopy and evidenced by formation of polymeric relief images after washout (65). Dye bleaching also resulted as shown in Fig. 7. 

No polymer formation occurred in any film containing only MB (though slow dye bleaching was observed in Elvamide films). Relative rates of polymer formation were determined in PVA films containing equimolar amounts of the activators NPG, TBBS, or TEOA. The rates obtained for freshly formed film samples and for films stored one day in the dark are shown in Table 6. The results parallel the solution studies described earlier. NPG is superior to the tin compound (TBBS) in photospeed. Both are better than the amine TEOA. However, after only one day of "aging," both the NPG and TEOA are inferior to TBBS, which does not suffer any speed loss on storage. 

The silver dye-bleach process depends on destruction of a dye in a photographic layer in an amount proportional to the quantity of image silver present.94 95 The dye is normally an azo dye in which the azo bond is cleaved. Over the years a variety of metal-complexed azo dyes have been described for use in this process. These dyes must be immobile they must not wander from layer to layer, or color contamination of the final image will result. However, they must be reactive enough in an aqueous environment for the azo bond to break. 

In another application the dyes used in the dye-bleach process are not premetallized however, they contain metallizable sites so that after the bleaching step an after-bath treatment with a transition metal solution yields the metal-complexed dye. Bisazo dyes such as (35) yield greenish blue images after processing and treatment with a copper or nickel acetate solution.99 Complex-ation can and presumably does occur at more than one site in the molecule. 

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