Ultrafast reaction dynamics of auramine O in a cyclodextrin nanocavity

The effect of confinement on a barrierless ultrafast chemical reaction is investigated through the ultrafast torsional reaction of the dye Auramine O bound in a cyclodextrin (CD) inclusion complex. The rate of the barrierless reaction is inferred from the ultrafast time evolution of the fluorescence emission. The rate is decreased on formation of the complex but in a highly size dependent fashion, with only β-CD yielding a significant effect. This reflects both the formation constant for the AuO-CD complex and the nature of the confinement. Even in the case of β-CD the effect of adsorption was smaller than was observed for adsorption of the same dye at the surfactant water interface. This shows that the structure and nature of the inclusion complex and is more important in determining the degree of rate retardation than the simple fact of confinement.