Photographic Sensitizing Dyes

Hamer s book in this series (1). which reviewed the synthesis of sensitizing dyes, their physical characteristics, and general photographic properties up to 1958, remains the basic encyclopedic source for the study of methine dyes. 

Many patents and studies are still published in the field of thiazolo dyes because the photographic industrx is always looking for new sensitizing dyes with improved efficiency and eager to know more about the mechanisms of their action on silver halide. 

Sensitizers as well as desensitizers form a reversal oxidoreduction system with silver halides, according to both pH and pAg of the photographic emulsion. But besides the specific influence of the emulsion, the efficiency of a sensitizing dye depends on many other factors such as its adsorption, its spectral absorption, the energetic transfer yield, the dye aggregate to the silver halide, and finally on its desensitizing property in... 

Selenazoles and their derivatives, that is. selenazolines and selenazo-lidines. aremainh used in cyanine-type dyes and photographic sensitizers as well as in pharmacology and chemotheraphs. 

An illustration of the technological significance of the relaxation phenomenon can be taken from photographic chemistry. Dyes of the cyanine class where Y = S, 0, CH—CH— n = 0,1,2,3...X = haUde, etc, are used as spectral sensitizers to extend photochemical response of the photographic silver hahdes, which only absorb blue and ultraviolet light, into the visible spectral regime. 

More recent research provides reversible oxidation-reduction potential data (17). These allow the derivation of better stmcture-activity relationships in both photographic sensitization and other systems where electron-transfer sensitizers are important (see Dyes, sensitizing). Data for an extensive series of cyanine dyes are pubflshed, as obtained by second harmonic a-c voltammetry (17). A recent "quantitative stmcture-activity relationship" (QSAR) (34) shows that Brooker deviations for the heterocycHc nuclei (discussed above) can provide estimates of the oxidation potentials within 0.05 V. An oxidation potential plus a dye s absorption energy provide reduction potential estimates. Different regression equations were used for dyes with one-, three-, five-methine carbons in the chromophore. Also noted in Ref. 34 are previous correlations relating Brooker deviations for many heterocycHc nuclei to the piC (for protonation/decolorization) for carbocyanine dyes the piC is thus inversely related to oxidation potential values. 

The detection of spectral sensitizing action often depends on amplification methods such as photographic or electrophotographic development or, alternatively, on chemical or biochemical detection of reaction products. Separation of the photosensitization reaction from the detection step or the chemical reaction allows selection of the most effective spectral sensitizers. Prime considerations for spectral sensitizing dyes include the range of wavelengths needed for sensitization and the absolute efficiency of the spectrally sensitized process. Because both sensitization wavelength and efficiency are important, optimum sensitizers vary considerably in their stmctures and properties. 

The pharmacological activities of other derivatives of these ring systems are examined intensively. Whereas other representatives of the above ring systems are patented as photographic sensitizers, catalysts for curing polyisocyanates, or dyes for acrylic nylon, polyester filters, and photographic material. 

Dye release developers are themselves colored molecules, the presence of which in silver halide photographic materials could interfere with light capture by the light-sensitive silver halide. Less light would be available to the sensitizing dyes. Another approach has been reported in which the leuco dye is linked to the coupling-off position of conventional photographic color... 

The sodium salt of the phenylglycine derivative (33) was investigated as an absorption promoter for the rectal absorption of beta-lactam antibiotics and insulin [80JAP(K)31040 81CPB1998, 81CPB2012], (Naphthothiazol-2-ylidene)malonates (1661 and 1662) were applied in silver halide photographic emulsions as sensitizer dyes [82JAP(K)54936]. 

Azo dyes containing indolizines have been extensively studied. Indolizines have been incorporated into mono- and poly-methine dyes, which have been used as photographic sensitizing and fabric brightening agents. 

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