Resonance Energy Transfer between Dye Molecules in Colloids of a Layered Silicate. The Effect of Dye Surface Concentration

Colloidal dispersions were prepared from a synthetic layered silicate of saponite type (Sap) and two cationic laser dyes, rhodamine 6G (R6G) and oxazine 4 (Ox4). The adsorption of dye molecules on Sap particles led to neither molecular aggregation nor segregation of dye molecules. Förster resonance energy transfer (FRET), investigated using steady-state and time-resolved fluorescence (TRF) spectroscopies, occurs from R6G to Ox4, and the efficiency increased with the surface concentration of adsorbed dye molecules, as determined by the dye/Sap ratio. Theoretical modeling of FRET based on defining probability density functions of intermolecular distances is presented. The theoretical model and experimental results were in very good agreement. Diffusion of the molecules might have contributed to the increase of FRET efficiency, especially at lower dye concentrations, whereas the influence of anisotropy factors was most likely negligible.