Effect of the layer charge of clay minerals on optical properties of organic dyes. A review

Interactions between clay minerals and cationic organic dyes cause significant changes in the optical, spectral and chemical properties of the chromophores. These changes are due to the formation of supramolecular assemblies of dye cations, called molecular aggregates. Numerous experiments indicate that dye molecular aggregation is sensitively controlled by the layer charge of a clay mineral. Interpretations are based on a detailed analysis of papers investigating reactions of dyes with clay minerals but also considering the reactions with other inorganic solid materials and templates. Older papers dealing with the subject and alternative interpretations of the phenomenon are analysed and critically reviewed. Significance for clay science, material sciences, nanotechnology and potential industrial applications are discussed.