A Spectroscopic Study of Xanthene Dyes on a Polystyrene Surface: an Investigation of Ion-π Interactions at Polymer Interfaces

Thin films of three differently charged xanthene dyes: rhodamine 6G (Rh6G, cationic), fluorescein 27 (F27, neutral), and disodium fluorescein (DSF, anionic) were cast onto a polystyrene (PS) coated glass substrate to investigate ion-π interactions. Absorbance spectroscopy was used to determine the aggregation state of the dyes on the PS surface. Deconvolution of the spectra of films revealed multiple peaks for all dyes assigned to isolated monomers, aggregates, and complexes between the dye and the polymer substrate. The shift of the low energy peak relative to the monomer peak was used as an indication of interaction strength of that species with the PS π system, which followed the trend of Rh6G > DSF > F27. Increase in the interaction energy is attributed to stabilization from ion-π interactions. Steady-state emission spectra and excited state lifetime measurements were performed on all films. The formation of a weakly emissive exciplex was found for Rh6G and DSF, consistent with ion-π interactions, but no evidence of an exciplex is found for the F27 films.