Spectral Properties, Formation of Dye Molecular Aggregates, and Reactions in Rhodamine 6G/Layered Silicate Dispersions

Abstract

A series of layered silicates with a systematically modified charge was prepared from montmorillonite, using the standard method of Li+ cation fixation. The effect of the charge of the prepared materials on the optical properties of the adsorbed cationic dye, Rhodamine 6G, was tested. The layer charge of the silicate substrate controlled the formation of the dye's molecular assemblies, such as H-dimers and H- and J-aggregates. The dye species (monomers, aggregates) were characterized by distinctly different optical properties. Ultraviolet/visible and fluorescence spectroscopies were used for the characterization of the studied systems. Time difference spectroscopy was applied for the investigation of the reactions, which proceeded in dispersions after mixing the dye solution with silicate. The reactions included the formation of higher order aggregates at the surfaces of the high charge densities or dye deaggregation reactions at the surfaces of medium or low charge densities. Some trends and features of the R6G aggregation and the changes with time in relation to the layer charge are different from those that have been observed for other dyes in older studies. This may be due to the complicated structure and the specific shape of the R6G cation.