Intercalation characteristics of 1,1 '-diethyl-2,2 '-cyanine and other cationic dyes in synthetic saponite: Orientation in the interlayer

The basal spacings of complexes of saponite with five cationic dyes, 1,1'-d iethyl-2,2'-cyanine, crystal violet, methylene blue, 1,1'-diethyl-2,2'-carb ocyanine, and 1,1'-diethyl-2,2'-dicarbocyanine, varied with degree of satur ation of each dye. At low loading of dye to saponite, each cationic dye sho wed nearly the same absorption spectrum in the UV-visible region as that of its dilute aqueous solution, whereas the spectrum changed distinctly at hi gh loading. With increasing degree of dye loading, the absorption band shif ted to longer wavelength for 1,1'-diethyl-2,2'-cyanine (J band) and to shor ter wavelength for the others (D, H bands). On the basis of the basal spaci ng of each respective dye-clay complex, the orientation of the intercalated dye molecules is proposed as follows: the major plane of the cationic dye lies horizontal to the 2:1 layer surface at low loading. With increasing lo ading, the dye molecules interact with adjacent dye molecules and orient ve rtically to the 2:1 layer at high loading near the cation-exchange capacity .