Study of the Eosin-Y/PAMAM interactions in alkaline aqueous solution

The interactions between the xanthene dye Eosin-Y (Eos) and amino-terminated PAMAM dendrimers of low generations (G0-G3) were studied in alkaline water solution. The effect of concentration and generation of the dendrimer on the photophysics of Eos was evaluated by means of absorption and fluorescence spectroscopies. The observed spectral changes were ascribed to the association dye/dendrimer. From these data, the Eos/PAMAM binding constants (Kbind) were determined, which strongly increased with the size of the dendrimer. Stationary fluorescence anisotropy and time-resolved single photon counting were also used to characterize the association process. The restriction in the rotational diffusion of the Eos increased as a function of the concentration and generation of PAMAM, as determined by anisotropy measurements. Biexponential fluorescence decays were obtained in the presence of G3, and the respective lifetimes were ascribed to free and bound Eos species. These results correlate with Kbind values and suggest the formation of host/guest system with larger dendrimers. Therefore, this environmentally-friendly dye/dendrimer system would be appropriate for potential applications in fields such as drugs delivery and photopolymerization.