It has long been known that many dyes aggregate in aqueous solution. The hypothesis was first suggested by Stegner(1420) and the earliest contributions in the field, both concerned with the spectral characteristics of aqueous solutions of dyes, were made by Formánek and Grandmougin(464) and Sheppard.(1374) The latter author concluded that the spectral changes observed were due to reversible molecular aggregation. Subsequent publications have dealt in detail with the state in aqueous solution of dyes both for textile usage and for photographic sensitizing processes. An understanding of the association of dyes in water is of some importance in studies of dyeing systems since practically all textile dyes are still applied from aqueous solutions, while the difference between good and bad sensitizing dyes may be explained in part by the inability of the latter to associate either in aqueous solution or when adsorbed on silver halides. Certain cationic dyes have recently been used to produce continuously tunable lasers and the dimerization of the dyes must be quenched by addition of surfactant. The self-association of dye ions may occur in water at concentrations as low as 1 mg liter−1 and is dependent on several factors. Thus reduction in temperature or increase in dye and inorganic electrolyte concentration causes increased association. The effects of dye concentration and temperature are reversible.
KeywordsMethylene Blue Acridine Orange Aggregation Number Pinacyanol Chloride Aqueous Spectrum
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