Resonance Energy Transfer between Rhodamine Molecules Adsorbed on Layered Silicate Particles

Forster resonance energy transfer (FRET) from rhodamine 123 (Rh 123; the energy donor (ED)) to rhodamine 610 (Rh610; the energy acceptor (EA)) adsorbed on the surface of synthetic saponite (SAP) was investigated. Experiments were performed with colloidal dispersions and thin solid films. In the colloidal systems, we observed efficient FRET leading to emission from the EA that was dependent on the molar ratio of the dyes. Self-quenching partially contributed to the relaxation of rhodamine molecules. Competitive adsorption of the dyes on SAP significantly influenced FRET under specific conditions. Adsorbed Rh610 was easily replaced by Rh 123, especially at high dye loadings, and by surfactant dodecyltrimethylammonium (C12TMA) cations, especially at high surfactant concentrations. Rh610 forms zwitterions via the hydrolysis of carboxyl groups. The presence of the anionic group in the Rh610 molecule contributes to the repulsion between the dye molecules and SAP colloid particles and to lower adsorption of the dye. With a large excess of the ED. very efficient FRET was observed for films with SAP, C12TMA cations, Rh123, and Rh610. The main role of the inorganic SAP template is to bring the interacting dye molecules close together but still prevent fluorescence quenching caused by dye molecular aggregation.