| Abstract
| - Films of the layered silicates fluorohectorite (FH) and saponite (Sap) with various rhodamine dyes wereprepared. The dyes with acidic as well as large hydrophobic groups in their molecule were not adsorbed onthe surface of FH, which was interpreted in terms of high charge density on the surface of this silicate. Alladsorbed dyes formed similar forms, such as isolated cations and H-type molecular aggregates, which werecharacterized by different spectral properties. Polarized ultraviolet−visible (UV−vis) spectroscopy was usedfor the characterization of the molecular orientation of dye chromophores on the silicate surface. The isolateddye cations and species, which absorbed light at the low energy part of the spectra, were only slightly tiltedwith respect to the plane of the silicate surface. The cations forming H-aggregates and absorbing light at lowwavelengths were oriented in a nearly perpendicular fashion. The nearly perpendicular orientation was observedas a strong increase of dichroic ratio with film tilting. The orientation of the cations in H-aggregates dependspartially on the structure of the dye molecule, namely, on the type of amino group (primary, secondary, ortertiary) in the dye molecule. The type of amino groups probably plays a role in the suitable orientation ofdye cations for effective electrostatic interaction between the cations and the negatively charged siloxanesurface. X-ray powder diffraction could not distinguish dye phases of dye monomers and molecular aggregates.
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