Structure of cationic dyes assemblies intercalated in the films of montmorillonite

Hybrid materials based on cationic organic dyes intercalated in oriented clay mineral films were prepared via dye adsorption from aqueous solutions on the films having been prepared by a spin-coating method. The films with four thiazine dyes thionine, azure A, azure B and methylene blue and one representative xanthene dye, pyronin Y (Py), were investigated. Four reduced charge montmorillonites (RCM) were used as clay mineral templates, representing a semi-synthetic series of materials of almost the same composition, but different in the layer charge and related properties. The interlayer structure was investigated using X-ray diffraction and linearly-polarized absorption spectroscopy in ultraviolet-visible region. The effects of the molecular structure of the dyes and the different layer charge densities of the clays mineral on the molecular orientation were studied. The structure of the assemblies was very similar for thiazine dyes, but different for the case of Py. In the latter case, the formation of bimolecular layers of Py cations led to a significantly higher interlayer expansion. Unusual structural properties of Py/RCM films were interpreted in terms of the presence of polar/non-polar zones in heteroaromatic skeleton of Py cation to influence dye cation aggregation to specific molecular assemblies. (C) 2008 Elsevier B.V. All rights reserved.