Ultrafast twisting motions and intramolecular charge-transfer reaction in a cyanine dye trapped in molecular nanocavities

Emission properties of the cyanine dye, 1-(2-naphthyl)-2-ethenyl-(2-benzothiazolium) iodide, in aqueous nanocavities offered by cyclodextrins and in a film of a polymeric matrix were studied by means of steady-state and picosecond time-resolved emission spectroscopy. The results show the occurrence of a fast twisting motion and a subsequent intramolecular charge-transfer reaction. The initial step can be prevented by the size of the nanocavity which governs the spectral position of the fluorescence band and lifetime of the excited encapsulated host.