Confined ultrafast torsional dynamics of Thioflavin-T in a nanocavity

The influence of confinement in the supramolecular β-cyclodextrin nanocavity on the excited state torsional dynamics of the amyloid fibril sensor, Thioflavin-T, is explored using subpicosecond fluorescence up-conversion spectroscopy. In the presence of β-cyclodextrin, the emission intensity and the fluorescence lifetime of Thioflavin-T significantly increases, indicating the confinement effect of the nanocage on the photophysical behaviour of the dye. Detailed time-resolved fluorescence studies show an appreciable dynamic Stokes' shift for the dye in the β-cyclodextrin nanocavity. Analysis of the time-resolved area normalized emission spectra (TRANES) indicates the formation of an emissive TICT state. The rate of formation of the TICT state, as calculated from the time dependent changes in the peak frequency and the width of the emission spectra, is found to be substantially slower in the β-cyclodextrin nanocavity compared to that in bulk water. Present results indicate that ultrafast torsional motion in Thioflavin-T is significantly retarded due to confinement by the β-cyclodextrin nanocavity.