| Abstract
| - Nanoparticles of synthetic Laponite clay can be coated with individual or mixed cyanine dyes to formJ-aggregated assemblies in water. The absorption and fluorescence characteristics of these J-aggregatesare substantially different from those of J-aggregates formed in crystals or colloids, suggesting that smallerJ-aggregate domains are present on the disk-shaped nanoparticles. The mixed cyanine/Laponite aggregatesexhibit similar but nonidentical absorption and fluorescence as compared to the individual dye aggregates,suggesting a mixed electronic structure. The fluorescence from the nanoparticle-adsorbed cyanines issubject to superquenching by a variety of electron- and energy-accepting quenchers. These quenchers canbe introduced by coadsorption with donors on the clay (mixed aggregates) or by addition of acceptors topreformed donor aggregates in aqueous suspensions. For some of the energy-accepting cyanines, it is foundthat strong sensitization of fluorescence from a (mostly) acceptor state is observed, even in cases wherethe monomer dye is non- or very weakly emissive. In limiting cases, 50% quenching is observed at levelsof 1 quencher per ∼400 monomers or 4 quenchers per nanoparticle.
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